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Bhardwaj, Ashutosh, Kamal Jain, and Rajat Subhra Chatterjee. "Refining IKONOS DEM for Dehradun Region Using Photogrammetry Based DEM Editing Methods, Orthoimage Generation and Quality Assessment of Cartosat-1 DEM." Environmental Sciences Proceedings 5, no. 1 (December 2, 2020): 3. http://dx.doi.org/10.3390/iecg2020-06966.
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The correct representation of the topography of terrain is an important requirement to generate photogrammetric products such as orthoimages and maps from high-resolution (HR) or very high-resolution (VHR) satellite datasets. The refining of the digital elevation model (DEM) for the generation of an orthoimage is a vital step with a direct effect on the final accuracy achieved in the orthoimages. The refined DEM has potential applications in various domains of earth sciences such as geomorphological analysis, flood inundation mapping, hydrological analysis, large-scale mapping in an urban environment, etc., impacting the resulting output accuracy. Manual editing is done in the presented study for the automatically generated DEM from IKONOS data consequent to the satellite triangulation with a root mean square error (RMSE) of 0.46, using the rational function model (RFM) and an optimal number of ground control points (GCPs). The RFM includes the rational polynomial coefficients (RPCs) to build the relation between image space and ground space. The automatically generated DEM initially represents the digital surface model (DSM), which is used to generate a digital terrain model (DTM) in this study for improving orthoimages for an area of approximately 100 km2. DSM frequently has errors due to mass points in hanging (floating) or digging, which need correction while generating DTM. The DTM assists in the removal of the geometric effects (errors) of ground relief present in the DEM (i.e., DSM here) while generating the orthoimages and thus improves the quality of orthoimages, especially in areas such as Dehradun that have highly undulating terrain with a large number of natural drainages. The difference image of reference, i.e., edited IKONOS DEM (now representing DTM) and automatically generated IKONOS DEM, i.e., DSM, has a mean difference of 1.421 m. The difference DEM (dDEM) for the reference IKONOS DEM and generated Cartosat-1 DEM at a 10 m posting interval (referred to as Carto10 DEM) results in a mean difference of 8.74 m.
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Frankenberg, Elizabeth, and Duncan Thomas. "Women's Health and Pregnancy Outcomes: Do Services Make a Difference?" Demography 38, no. 2 (2001): 253–65. http://dx.doi.org/10.1353/dem.2001.0014.
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London, Andrew S., and Cheryl Elman. "The Influence of Remarriage on the Racial Difference in Mother-Only Families in 1910." Demography 38, no. 2 (2001): 283–97. http://dx.doi.org/10.1353/dem.2001.0017.
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Zhou, Zhu Bo, Hong Zhang Ma, Xiao Bo Zhu, and Lin Sun. "Comparative Analysis of Forest Height Retrieval Methods by Polarimetric SAR Interferometry." Advanced Materials Research 726-731 (August 2013): 4686–89. http://dx.doi.org/10.4028/www.scientific.net/amr.726-731.4686.
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The objective of this paper is to compare and analyze the forest height retrieval methods from Polarimetric SAR Interferometry(POLINSAR).Both of the methods based on DEM difference and that on interferometry coherence amplitude are generalized, analyzed, and compared.Also in this paper combined methods of DEM difference and interferometry coherence amplitude are proposed and validated.The ESA fullpolarimetric interferometry L-band data are used for forest height analysis.The results show that the height is severely underestimated using DEM difference method,In constast,interferometry coherence amplitude method has a overest imation of height.The combined method of DEM difference and interferometry coherence amplitude has a much better estimate,closer to the true height than these two methods.
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Bernhard, Stefan, and Sarah Bernhard. "Do EU Anti-discrimination Provisions Make a Difference?" Zeitschrift für Soziologie 45, no. 1 (February 1, 2016): 57–72. http://dx.doi.org/10.1515/zfsoz-2015-1003.
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Zusammenfassung: Das Diskriminierungsverbot ist zwar ein wichtiger Grundsatz in der Europäischen Union (EU), über seine Auswirkungen innerhalb der Mitgliedsstaaten ist bisher allerdings wenig bekannt. Wir gehen davon aus, dass das Diskriminierungsverbot das Ausmaß von Lohndiskriminierung gegen EU-Ausländer auf den nationalen Arbeitsmärkten in der EU verringert. Diese Vermutung wird mit administrativen Prozessdaten überprüft, indem die Veränderungen von Lohnunterschieden zwischen vollzeitbeschäftigten deutschen und ausländischen Männern auf dem westdeutschen Arbeitsmarkt mit Juhn-Murphy-Pierce-Zerlegungen analysiert werden. Die Ergebnisse stützen die Hypothese: Während die Lohndiskriminierung für die meisten untersuchten Gruppen von EU-Ausländern nach dem Beitritt ihrer Herkunftsländer zurückgegangen ist, lässt sich für die meisten Ausländergruppen aus Drittstaaten gestiegene oder konstante Lohndiskriminierung beobachten. Die europäischen Nichtdiskriminierungsregeln und die mit ihnen verbundenen Übertragungsmechanismen wirken demnach in die intendierte Richtung.
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Fu, C. Y., and J. R. Tsay. "STATISTIC TESTS AIDED MULTI-SOURCE DEM FUSION." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B6 (June 17, 2016): 227–33. http://dx.doi.org/10.5194/isprs-archives-xli-b6-227-2016.
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Since the land surface has been changing naturally or manually, DEMs have to be updated continually to satisfy applications using the latest DEM at present. However, the cost of wide-area DEM production is too high. DEMs, which cover the same area but have different quality, grid sizes, generation time or production methods, are called as multi-source DEMs. It provides a solution to fuse multi-source DEMs for low cost DEM updating. The coverage of DEM has to be classified according to slope and visibility in advance, because the precisions of DEM grid points in different areas with different slopes and visibilities are not the same. Next, difference DEM (dDEM) is computed by subtracting two DEMs. It is assumed that dDEM, which only contains random error, obeys normal distribution. Therefore, student test is implemented for blunder detection and three kinds of rejected grid points are generated. First kind of rejected grid points is blunder points and has to be eliminated. Another one is the ones in change areas, where the latest data are regarded as their fusion result. Moreover, the DEM grid points of type I error are correct data and have to be reserved for fusion. The experiment result shows that using DEMs with terrain classification can obtain better blunder detection result. A proper setting of significant levels (α) can detect real blunders without creating too many type I errors. Weighting averaging is chosen as DEM fusion algorithm. The priori precisions estimated by our national DEM production guideline are applied to define weights. Fisher’s test is implemented to prove that the priori precisions correspond to the RMSEs of blunder detection result.
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Fu, C. Y., and J. R. Tsay. "STATISTIC TESTS AIDED MULTI-SOURCE DEM FUSION." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B6 (June 17, 2016): 227–33. http://dx.doi.org/10.5194/isprsarchives-xli-b6-227-2016.
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Since the land surface has been changing naturally or manually, DEMs have to be updated continually to satisfy applications using the latest DEM at present. However, the cost of wide-area DEM production is too high. DEMs, which cover the same area but have different quality, grid sizes, generation time or production methods, are called as multi-source DEMs. It provides a solution to fuse multi-source DEMs for low cost DEM updating. The coverage of DEM has to be classified according to slope and visibility in advance, because the precisions of DEM grid points in different areas with different slopes and visibilities are not the same. Next, difference DEM (dDEM) is computed by subtracting two DEMs. It is assumed that dDEM, which only contains random error, obeys normal distribution. Therefore, student test is implemented for blunder detection and three kinds of rejected grid points are generated. First kind of rejected grid points is blunder points and has to be eliminated. Another one is the ones in change areas, where the latest data are regarded as their fusion result. Moreover, the DEM grid points of type I error are correct data and have to be reserved for fusion. The experiment result shows that using DEMs with terrain classification can obtain better blunder detection result. A proper setting of significant levels (α) can detect real blunders without creating too many type I errors. Weighting averaging is chosen as DEM fusion algorithm. The priori precisions estimated by our national DEM production guideline are applied to define weights. Fisher’s test is implemented to prove that the priori precisions correspond to the RMSEs of blunder detection result.
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Borlaf-Mena, Ignacio, Maurizio Santoro, Ludovic Villard, Ovidiu Badea, and Mihai Andrei Tanase. "Investigating the Impact of Digital Elevation Models on Sentinel-1 Backscatter and Coherence Observations." Remote Sensing 12, no. 18 (September 16, 2020): 3016. http://dx.doi.org/10.3390/rs12183016.
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Spaceborne remote sensing can track ecosystems changes thanks to continuous and systematic coverage at short revisit intervals. Active remote sensing from synthetic aperture radar (SAR) sensors allows day and night imaging as they are not affected by cloud cover and solar illumination and can capture unique information about its targets. However, SAR observations are affected by the coupled effect of viewing geometry and terrain topography. The study aims to assess the impact of global digital elevation models (DEMs) on the normalization of Sentinel-1 backscattered intensity and interferometric coherence. For each DEM, we analyzed the difference between orbit tracks, the difference with results obtained with a high-resolution local DEM, and the impact on land cover classification. Tests were carried out at two sites located in mountainous regions in Romania and Spain using the SRTM (Shuttle Radar Topography Mission, 30 m), AW3D (ALOS (Advanced Land Observation Satellite) World 3D, 30 m), TanDEM-X (12.5, 30, 90 m), and Spain national ALS (aerial laser scanning) based DEM (5 m resolution). The TanDEM-X DEM was the global DEM most suitable for topographic normalization, since it provided the smallest differences between orbital tracks, up to 3.5 dB smaller than with other DEMs for peak landform, and 1.4–1.9 dB for pit and valley landforms.
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Argys, Laura M., and Susan L. Averett. "The effect of family size on education: new evidence from China's one-child policy." Journal of Demographic Economics 85, no. 1 (March 2019): 21–42. http://dx.doi.org/10.1017/dem.2018.22.
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AbstractEconomists theorize that the inverse relationship between income and family size reflects a trade-off between child quality and quantity. Testing this hypothesis requires addressing the simultaneity of the quality and quantity decisions. The unanticipated birth of twins and sex composition of the first two children have been used as the exogenous variation in family size with mixed results. We exploit the One-Child Policy (OCP) in China, which exogenously reduced fertility, and examine how the OCP affected the education of Chinese migrants to the USA. Using the American Community Survey and a difference-in-differences strategy, we find higher levels of education for Chinese migrants born after the OCP compared with their counterparts from other East Asian countries. This finding provides additional support for the existence of a quality-quantity trade-off.
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Liu, Zhiheng, Ling Han, Zhaohui Yang, Hongye Cao, Fengcheng Guo, Jianhua Guo, and Yiqi Ji. "Evaluating the Vertical Accuracy of DEM Generated from ZiYuan-3 Stereo Images in Understanding the Tectonic Morphology of the Qianhe Basin, China." Remote Sensing 13, no. 6 (March 22, 2021): 1203. http://dx.doi.org/10.3390/rs13061203.
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Currently available high-resolution digital elevation model (DEM) is not particularly useful to geologists for understanding the long-term changes in fluvial landforms induced by tectonic uplift, although DEMs that are generated from satellite stereo images such as the ZiYuan-3 (ZY3) satellite include characteristics with significant coverage and rapid acquisition. Since an ongoing analysis of fluvial systems is lacking, the ZY3 DEM was generated from block adjustment to describe the mountainous area of the Qianhe Basin that have been induced by tectonic uplift. Moreover, we evaluated the overall elevation difference in ZY3 DEM, Shuttle Radar Topography Mission (1″ × 1″) (SRTM1), and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) by using the Ice Cloud and Land Elevation Satellite/Geoscience Laser Altimeter (ICESat/GLAH14) point cloud and a DEM of 1:50,000 scale. The values of the root mean square error (RMSE) of the elevation difference for ZY3 DEM were 9.31 and 9.71 m, respectively, and are in good agreement with SRTM1. The river long profiles and terrace heights were also extracted to compare the differences in channel steepness and the incision rates with SRTM1 and ASTER GDEM. Our results prove that ZY3 DEM would be a good alternative to SRTM1 in achieving the 1:50,000 scale for DEM products in China, while ASTER GDEM is unsuitable for extracting river longitudinal profiles. In addition, the northern and southern river incision rates were estimated using the ages and heights of river terraces, demonstrating a range from 0.12–0.45 to 0.10–0.33 m/kyr, respectively. Collectively, these findings suggest that ZY3 DEM is capable of estimating tectonic geomorphological features and has the potential for analyzing the continuous evolutionary response of a landscape to changes in climate and tectonics.
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Bean, Frank D., Rodolfo Corona V., Rodolfo Tuiran, Karen A. Woodrow-Lafield, and Jennifer V. W. Van Hook. "Circular, Invisible, and Ambiguous Migrants: Components of Difference in Estimates of the Number of Unauthorized Mexican Migrants in the United States." Demography 38, no. 3 (2001): 411–22. http://dx.doi.org/10.1353/dem.2001.0023.
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Khasanov, Khojiakbar, and Azamat Ahmedov. "Comparison of Digital Elevation Models for the designing water reservoirs: a case study Pskom water reservoir." E3S Web of Conferences 264 (2021): 03058. http://dx.doi.org/10.1051/e3sconf/202126403058.
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This study investigates the accuracy of various DEMs (SRTM DEM, ASTER GDEM, and ALOS PALSAR DEM) for the area of the designing Pskom water reservoir (recommended to construction in Pskom River, in Tashkent region. DEMs are compared for the study area using the Global Mapper application and selection Ground Control Points (GCP). The RMSE we calculate is the most easily interpreted statistic as the square root of the mean square error because it has the same units as the quantity drawn on the vertical axis. Results show that SRTM based measurements of ground control points (GCPs) exhibit RMSE of 15.72 m while ASTER DEM based measurements exhibits and RMSE of 18.47 m, ALOS PALSAR exhibit RMSE of 14.02 m for the Water reservoir located in the plain. There are AOS PALSAR outperforms SRTM and ASTER DEM in detecting vertical accuracy. Based on the capabilities of the Global Mapper program, we can build the longitudinal profile of the approximate location where the dam can be built in each DEM and compare. The results obtained show that the dam height is 187 m at ALOS PALSAR DEM, 168 m at ASTER GDEM, and 175 m at SRTM. The study found that using ALOS PALSAR data in the design of the proposed Pskom Reservoir for construction leads to a more accurate result. Comparing the DEMs data shows that there is more difference between the vertical accuracy; the horizontal accuracy level is almost the same. The results were obtained using ALOS PALSAR data in determining the storage volume (W=479368568 m3) and area (F=8.31 sq., km) of the water reservoir.
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Chidi, Chhabi Lal, Wei Zhao, Suresh Chaudhary, Donghong Xiong, and Yanhong Wu. "Sensitivity Assessment of Spatial Resolution Difference in DEM for Soil Erosion Estimation Based on UAV Observations: An Experiment on Agriculture Terraces in the Middle Hill of Nepal." ISPRS International Journal of Geo-Information 10, no. 1 (January 13, 2021): 28. http://dx.doi.org/10.3390/ijgi10010028.
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Soil erosion in the agricultural area of a hill slope is a fundamental issue for crop productivity and environmental sustainability. Building terrace is a very popular way to control soil erosion, and accurate assessment of the soil erosion rate is important for sustainable agriculture and environmental management. Currently, many soil erosion estimations are mainly based on the freely available medium or coarse resolution digital elevation model (DEM) data that neglect micro topographic modification of the agriculture terraces. The development of unmanned aerial vehicle (UAV) technology enables the development of high-resolution (centimeter level) DEM to present accurate topographic features. To demonstrate the sensitivity of soil erosion estimates to DEM resolution at this high-resolution level, this study tries to evaluate soil erosion estimation in the Middle Hill agriculture terraces in Nepal based on UAV derived high-resolution (5 × 5 cm) DEM data and make a comparative study for the estimates by using the DEM data aggregated into different spatial resolutions (5 × 5 cm to 10 × 10 m). Firstly, slope gradient, slope length, and topographic factors were calculated at different resolutions. Then, the revised universal soil loss estimation (RUSLE) model was applied to estimate soil erosion rates with the derived LS factor at different resolutions. The results indicated that there was higher change rate in slope gradient, slope length, LS factor, and soil erosion rate when using DEM data with resolution from 5 × 5 cm to 2 × 2 m than using coarser DEM data. A power trend line was effectively used to present the relationship between soil erosion rate and DEM resolution. The findings indicated that soil erosion estimates are highly sensitive to DEM resolution (from 5 × 5 cm to 2 × 2 m), and the changes become relatively stable from 2 × 2 m. The use of DEM data with pixel size larger than 2 × 2 m cannot detect the micro topography. With the insights about the influencing mechanism of DEM resolution on soil erosion estimates, this study provides important suggestions for appropriate DEM data selection that should be investigated first for accurate soil erosion estimation.
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Ghuffar, Sajid. "DEM Generation from Multi Satellite PlanetScope Imagery." Remote Sensing 10, no. 9 (September 13, 2018): 1462. http://dx.doi.org/10.3390/rs10091462.
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Planet Labs have recently launched a large constellation of small satellites (3U cubesats) capable of imaging the whole Earth landmass everyday. These small satellites capture multiple images of an area on consecutive days or sometimes on the same day with a spatial resolution of 3–4 m. Planet Labs endeavors to operate the constellation in a nadir pointing mode, however, the view angle of these satellites currently varies within a few degrees from the nadir leading to varying B/H ratio for overlapping image pairs. Due to relatively small scene footprint and small off-nadir angle, the baseline to height ratio (B/H) of the overlapping PlanetScope images is often less than 1:10, which is not ideal for 3D reconstruction. Therefore, this paper explores the potential of Digital Elevation Model generation from this multi-date, multi-satellite PlanetScope imagery. The DEM generation from multiple PlanetScope images is achieved using a volumetric stereo reconstruction technique, which applies semi global matching in georeferenced object space. The results are evaluated using a LiDAR based DEM (5 m) over Mount Teide (3718 m) in Canary Islands and the ALOS (30 m) DEM on rugged terrain of the Nanga Parbat massif (8126 m) in the western Himalaya range. The proposed methodology is then applied on images from two PlanetScope satellites overpasses within a couple of minutes difference to compute the DEM of the Khurdopin glacier in the Karakoram range, known for its recent surge. The quantitative assessment of the generated elevation models is done by comparing statistics of the elevation differences between the reference LiDAR and ALOS DEM and the PlanetScope DEM. The Normalized Median of Absolute Deviation (NMAD) of the elevation differences between the computed PlanetScope DEM and LiDAR DEM is 4.1 m and the elevation differences for the ALOS DEM over stable terrain is 3.9 m. The results show that PlanetScope imagery can lead to sufficient quality DEM even with a small baseline to height ratio. Therefore, the daily PlanetScope imagery is a valuable data source and the DEM generated from this imagery can potentially be employed in numerous applications requiring multi temporal DEMs.
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Carson, Scott Alan. "NET NUTRITION AND THE TRANSITION FROM 19TH CENTURY BOUND TO FREE-LABOR: ASSESSING DIETARY CHANGE WITH DIFFERENCES-IN-DECOMPOSITIONS." Journal of Demographic Economics 84, no. 4 (October 17, 2018): 447–75. http://dx.doi.org/10.1017/dem.2018.15.
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Abstract:Average stature reflects cumulative net nutrition and health during economic development. This study introduces a difference-in-decompositions approach to show that although 19th century African-American cumulative net nutrition was comparable to working class whites, it was made worse-off with the transition to free-labor. Average stature reflects net nutrition over the life-course, and adult blacks born under bound-labor had greater age related statures loss than blacks under free-labor. Agricultural worker's net nutrition was better than workers in other occupations and was better-off under free-labor and industrialization. Within-group stature variation was greater than across-group variation, and white within-group stature variation associated with socioeconomic status was greater than African-Americans.
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Geng, Tong, Shengkai Zhang, Feng Xiao, Jiaxing Li, Yue Xuan, Xiao Li, and Fei Li. "DEM Generation with ICESat-2 Altimetry Data for the Three Antarctic Ice Shelves: Ross, Filchner–Ronne and Amery." Remote Sensing 13, no. 24 (December 17, 2021): 5137. http://dx.doi.org/10.3390/rs13245137.
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The ice shelf is an important component of the Antarctic system, and the interaction between the ice sheet and the ocean often proceeds through mass variations of the ice shelf. The digital elevation model (DEM) of the ice shelf is particularly important for ice shelf elevation change and mass balance estimation. With the development of satellite altimetry technology, it became an important data source for DEM research of Antarctica. The National Aeronautics and Space Administration (NASA) Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) launched in 2018 is a significant improvement in along-track sampling rate and measurement accuracy compared with previous altimetry satellites. This study uses ordinary kriging interpolation to present new DEMs (ICESat-2 DEM hereinafter) for the three ice shelves (Ross, Filchner–Ronne and Amery) in Antarctica with ICESat-2 altimetry data. Two variogram models (linear and spherical) of ordinary kriging interpolation are compared in this paper. The result shows that the spherical model generally shows better performance and lower standard deviation (STD) than the linear models. The precision of the ultimate DEM was evaluated by NASA Operation IceBridge (OIB) data and compared with five previously published Antarctic DEM products (REMA, TanDEM-X PolarDEM, Slater DEM, Helm DEM, and Bamber DEM). The comparison reveals that the mean difference between ICESat-2 DEM of the Ross ice shelf and OIB is −0.016 m with a STD of 0.918 m, and the mean difference between ICESat-2 DEM of the Filchner–Ronne ice shelf and OIB is −0.533 m with a STD of 0.718 m. The three ICESat-2 DEMs show higher spatial resolution and elevation accuracy than five previously published Antarctic DEMs.
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Zhou, Zai Hui, Jing Ma, and Wu Di Xu. "Establishes the Precise Three-Dimensional Terrain Method Study Based on Anudem." Applied Mechanics and Materials 416-417 (September 2013): 1142–46. http://dx.doi.org/10.4028/www.scientific.net/amm.416-417.1142.
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Take a typical region in the Loess Plateau of North Shaanxi Province zone as the study area.Based on relief map with a scale of 1:1000 to generate accurate 3D terrain DEM using Anudem algorithm. Compared with the production of Anudem method TIN method and Kriging method between DEM. DEM accuracy evaluation including value target, profile and slope and terrain attribute visualization, contour line playbacking and different differential value algorithm result variance analysis. The DEM difference that the result demonstrates that the different algorithm obtains is big, and DEM precision of Anudem method production is best, can very good response precise three-dimensional terrain.
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Al-Doski, Jwan, Faez M. Hassan, Hussein Abdelwahab Mossa, and Aus A. Najim. "Incorporation of Digital Elevation Model, Normalized Difference Vegetation Index, and Landsat-8 Data for Land Use Land Cover Mapping." Photogrammetric Engineering & Remote Sensing 88, no. 8 (August 1, 2022): 507–16. http://dx.doi.org/10.14358/pers.21-00082r2.
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Ancillary data are crucial in land use land cover (LULC) mapping process. This study goal is to investigate if adding Normalized Difference Vegetation Index (NDVI) and digital elevation model (DEM) data as ancillary data to the Landsat-8 spectral imagery (acquired on 14 April 2016) in the support vector machine (SVM ) classification process improves LULC mapping accuracy in GuaMusang, Malaysia. ENVI software was used to preprocess a single Landsat-8 image, convert it to reflectance, and calculate NDVI. ASTER-GDEM data were used to generate the DEM. The logical channel method was used to combine NDVI and DEM with Landsat-8 bands and limit the impact of shadows during SVM classification. The SVM accuracy was tested and evaluated on ancillary data and Landsat-8 spectral-based collection. The results revealed that the user's accuracy and producer's accuracy improved by 15.1% and 2.1%, for primary forest and by 17.93% and 28.86% for secondary forest, respectively. The classification reliability of the majority of LULC categories has increased significantly. Compared to SVM spectral-based set, the overall accuracy and kappa coefficient of the SVM ancillary-based set improved by 8.77% and 0.12, respectively. In conclusion, this article demonstrated that integrating DEM and NDVI data improves Landsat-8 image classification precision.
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Lin, Xiaohui, Gang Li, Fangchen Xu, Kehong Zeng, Jixu Xue, Wenming Yang, and Fei Wang. "A coupled SPH-DEM approach for modeling of free-surface debris flows." AIP Advances 12, no. 12 (December 1, 2022): 125018. http://dx.doi.org/10.1063/5.0106333.
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A Lagrangian mesh-less model is proposed to simulate fluid–solid flows with multiple-sized solids, i.e., millimeter-sized particle and larger-sized debris. Considering the difference in the size of solid phases, a hybrid resolved and unresolved model is established based on the coupling method of smoothed particle hydrodynamics (SPH) and discrete element method (DEM). SPH is used to model fluid, and the locally averaged Navier–Stokes equations are adopted as governing equations. DEM is used to model the particle–particle interactions, and the unresolved description of hydrodynamic forces including drag and buoyancy is established. The large-sized debris is modeled as the rigid body, which is discretized by particle elements having both SPH and DEM characteristics, where SPH particle elements are involved in the closure of the SPH fluids, and DEM particle elements interact with the solid particles following the contact law. The numerical model is validated and verified by several examples, including single-particle sedimentation, collapse of cylinder columns, and debris dam break. Results show that the present model reproduces general features of the complex fluid–solid flow with free surfaces. The advantage of the hybrid model is that it can deal with the fluid–solid flow problem with both small particles and large objects at a suitable resolution, and it is especially good at dealing with the free surface flow problem. A discretization for the modeling of debris flows is proposed based on the coupled SPH-DEM method. The novelty of the work is a coupled resolved–unresolved scheme for the free surface flow with multi-sized solids. The present scheme allows using a uniform resolution by bridging the size difference between small-scale solid particles and large-scale debris. The unresolved model of fluid-particle flow is efficient because the fluid resolution can be configured comparably to the particle size. The unified nature of the model allows the combination of resolved and unresolved simulations in the same computational domain.
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Feng, Y. T., and Yuanqiang Tan. "On Minkowski difference-based contact detection in discrete/discontinuous modelling of convex polygons/polyhedra." Engineering Computations 37, no. 1 (August 12, 2019): 54–72. http://dx.doi.org/10.1108/ec-03-2019-0124.
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Purpose Contact detection for convex polygons/polyhedra has been a critical issue in discrete/discontinuous modelling, such as the discrete element method (DEM) and the discontinuous deformation analysis (DDA). The recently developed 3D contact theory for polyhedra in DDA depends on the so-called entrance block of two polyhedra and reduces the contact to evaluate the distance between the reference point to the corresponding entrance block, but effective implementation is still lacking. Design/methodology/approach In this paper, the equivalence of the entrance block and the Minkowski difference of two polyhedra is emphasised and two well-known Minkowski difference-based contact detection and overlap computation algorithms, GJK and expanding polytope algorithm (EPA), are chosen as the possible numerical approaches to the 3D contact theory for DDA, and also as alternatives for computing polyhedral contact features in DEM. The key algorithmic issues are outlined and their important features are highlighted. Findings Numerical examples indicate that the average number of updates required in GJK for polyhedral contact is around 6, and only 1 or 2 iterations are needed in EPA to find the overlap and all the relevant contact features when the overlap between polyhedra is small. Originality/value The equivalence of the entrance block in DDA and the Minkowski difference of two polyhedra is emphasised; GJK- and EPA-based contact algorithms are applied to convex polyhedra in DEM; energy conservation is guaranteed for the contact theory used; and numerical results demonstrate the effectiveness of the proposed methodologies.
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Niu, Y., C. Zhao, J. Zhang, L. Wang, B. Li, and L. Fan. "RESEARCH ON A DEM COREGISTRATION METHOD BASED ON THE SAR IMAGING GEOMETRY." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-3 (April 30, 2018): 1333–38. http://dx.doi.org/10.5194/isprs-archives-xlii-3-1333-2018.
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Due to the systematic error, especially the horizontal deviation that exists in the multi-source, multi-temporal DEMs (Digital Elevation Models), a method for high precision coregistration is needed. This paper presents a new fast DEM coregistration method based on a given SAR (Synthetic Aperture Radar) imaging geometry to overcome the divergence and time-consuming problem of the conventional DEM coregistration method. First, intensity images are simulated for two DEMs under the given SAR imaging geometry. 2D (Two-dimensional) offsets are estimated in the frequency domain using the intensity cross-correlation operation in the FFT (Fast Fourier Transform) tool, which can greatly accelerate the calculation process. Next, the transformation function between two DEMs is achieved via the robust least-square fitting of 2D polynomial operation. Accordingly, two DEMs can be precisely coregistered. Last, two DEMs, i.e., one high-resolution LiDAR (Light Detection and Ranging) DEM and one low-resolution SRTM (Shutter Radar Topography Mission) DEM, covering the Yangjiao landslide region of Chongqing are taken as an example to test the new method. The results indicate that, in most cases, this new method can achieve not only a result as much as 80 times faster than the minimum elevation difference (Least Z-difference, LZD) DEM registration method, but also more accurate and more reliable results.
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Huang, Y., and Q. Hu. "CO-REGISTRATION OF MULTI-TEMPORAL DEM BASED ON SIFT ALGORITHM FOR CHANGE DETECTION OF GLACIERS." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-2/W7 (September 13, 2017): 747–52. http://dx.doi.org/10.5194/isprs-archives-xlii-2-w7-747-2017.
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To detect the change of geographic objects by using multi-temporal DEM, the data must be co-registered firstly. In this paper, the Scale-Invariant Feature Transform (SIFT) algorithm is used to co-register multi-temporal DEM data and glacier change detection. Firstly, the DEM is converted into image space and extracts feature information, calculate multiple sets of match point coordinates, and achieve swift and accurate DEM data co-registration using SIFT algorithm. Secondly, the difference between co-registered DEM datasets are analysed. Total area change and average rate of change are calculated. Finally, the change of multi-temporal DEM data of glaciers in Langkazi County, Tibet from 2004 to 2014 is detected using the method proposed in this paper. The results indicate that the proposed method is able to detect change of the glaciers and the overall accuracy is higher than 85 %.
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Li, W. M., E. X. Chen, Z. Y. Li, C. Jiang, and Y. Jia. "EVALUATION OF AIRBORNE L- BAND MULTI-BASELINE POL-INSAR FOR DEM EXTRACTION BENEATH FOREST CANOPY." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-3 (April 30, 2018): 949–53. http://dx.doi.org/10.5194/isprs-archives-xlii-3-949-2018.
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DEM beneath forest canopy is difficult to extract with optical stereo pairs, InSAR and Pol-InSAR techniques. Tomographic SAR (TomoSAR) based on different penetration and view angles could reflect vertical structure and ground structure. This paper aims at evaluating the possibility of TomoSAR for underlying DEM extraction. Airborne L-band repeat-pass Pol-InSAR collected in BioSAR 2008 campaign was applied to reconstruct the 3D structure of forest. And sum of kronecker product and algebraic synthesis algorithm were used to extract ground structure, and phase linking algorithm was applied to estimate ground phase. Then Goldstein cut-branch approach was used to unwrap the phases and then estimated underlying DEM. The average difference between the extracted underlying DEM and Lidar DEM is about 3.39 m in our test site. And the result indicates that it is possible for underlying DEM estimation with airborne L-band repeat-pass TomoSAR technique.
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Zhdanov, A. Y., A. V. Pankin, and A. V. Rentel. "Algorithm of adaptive correction of structural landforms on global digital elevation models." Geodesy and Cartography 937, no. 7 (August 20, 2018): 57–64. http://dx.doi.org/10.22389/0016-7126-2018-937-7-57-64.
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Due to various factors, such as the interpolation step or automatic correlators specifics, global digital elevation models (DEM) often have an effect of understating the heights, which leads to inaccurate display of structural landforms e.g. ridges. The algorithm of adaptive correction of structural landforms elevation on DEM is proposed in this article. The algorithm consists of two stages. In the first stage, an automatic classification of structural forms is performed based on height difference between neighboring DEM elements. In the second stage, the DEM elements are corrected based on the assigned classes. Adaptivity of the algorithm allows to use it for any kind of terrain and elevation ranges. The algorithm was tested on the global DEM ALOS World 3D (ALOS W3D30); the accuracy was assessed by geodetic reference network and ICESat mission data. The developed algorithm shows an improvement of DEM accuracy, especially in high-altitude areas, and it also helps to reveal areas requiring additional verification.
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ZHAO, Mingwei, Guoan TANG, Lei ZHANG, Jian TIAN, and Xiaodong SONG. "The DEM Based 5-Node Second-order Finite Difference Model for Slope Computation." Geo-information Science 14, no. 3 (November 27, 2012): 286–91. http://dx.doi.org/10.3724/sp.j.1047.2012.00286.
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Li, Yishi, Leping Chen, Daoxiang An, and Dong Feng. "An Extracting DEM Method Based on The Sub-apertures Difference in CSAR Mode." International Journal of Remote Sensing 43, no. 1 (January 2, 2022): 370–91. http://dx.doi.org/10.1080/01431161.2021.2018150.
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Dantas, Ana Alice Rodrigues, and Adriano Rolim Paz. "Use of HAND terrain descriptor for estimating flood-prone areas in river basins." Revista Brasileira de Ciências Ambientais 56, no. 3 (2021): 501–16. http://dx.doi.org/10.5327/z21769478892.
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The flood hazard mapping in a river basin is crucial for flooding risk management, mitigation strategies, and flood forecasting and warning systems, among other benefits. One approach for this mapping is based on the HAND (Height Above Nearest Drainage) terrain descriptor, directly derived from the Digital Elevation Model (DEM), in which each pixel represents the elevation difference of this point in relation to the river drainage network to which it is connected. Considering the Mamanguape river basin (3,522.7 km²; state of Paraíba, Brazil) as the study location, the present research applied this method and verified it as for five aspects: consideration of a spatially variable minimum drainage area for denoting the river drainage initiation; the impact of considering a depressionless DEM; evaluation of hydrostatic condition; effect of incorporating an existing river vector network; and comparative analysis of basin morphology regarding longitudinal river profiles. According to the results, adopting a uniform minimum drainage area for the river network initiation is a simplification that should be avoided, using a spatially variable approach, which influences the amount and spatial distribution of flooded areas. Additionally, considering the depressionless DEM leads to higher values of HAND and to a smaller flooded area (difference ranging between 3% and 99%), when compared with the use of DEM with depression, despite 3.1% of the pixels representing depressions. The use of the depressionless DEM is recommended, whereas the DEM pre-processing by incorporating a vector network (stream burning) generates dubious results regarding the relation between HAND and the morphological pattern presented in the DEM. Moreover, the estimation of flooded areas based on HAND does not guarantee the hydrostatic condition, but this disagreement comprises a negligible area for practical purposes.
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Kraus, Jaroslav. "Statistical Disclosure Control Methods for Harmonised Protection of Census Data: a Grid Case." Demografie 63, no. 4 (2021): 199–215. http://dx.doi.org/10.54694/dem.0285.
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The 2011 Population and Housing Census in the Czech Republic was accompanied by a significant change in the technology used to prepare course of the fieldwork, along with changes in how the data are processed and how the outputs are disseminated. Grids are regular polygon networks that divide the territory of country in a grid-like way/pattern into equally large territorial units, to which aggregate statistical data are assigned. The disadvantage of grids is that these are territorially small units that are often minimally populated. This mainly has implications for the protection of individual data, which is associated with statistical disclosure control (SDC). The research question addressed in this paper is whether data protection (perturbation methods) leads to a change in the characteristics of the file either in terms of statistics of the whole file (i.e. for all grids) or in terms of spatial statistics, which indicate the spatial distribution of the analysed phenomenon. Two possible solutions to the issue of grid data protection are discussed. One comes from the Statistical Office of the European Communities (Eurostat) and the other from Cantabular, which is a product of the Sensible Code Company (SCC) based in Belfast. According to the Cantabular methodology, one variant was processed, while according to the Eurostat methodology, two variants were calculated, which differ by the parameter settings for maximum noise D and the variance of noise V. The results of the descriptive statistics show a difference in absolute differences when Cantabular and Europstat solutions are compared. In the case of other statistics, the results are fully comparable. This paper is devoted to one specific type of census output. The question is to what extent these results are relevant for other types of census outputs. They differ fundamentally in the number of dimensions (grids have only two dimensions). It would therefore be appropriate to use SDC procedures that allow greater flexibility in defining SDC parameters.
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Padró, Joan-Cristian, Johnsson Cardozo, Pau Montero, Roger Ruiz-Carulla, Josep Maria Alcañiz, Dèlia Serra, and Vicenç Carabassa. "Drone-Based Identification of Erosive Processes in Open-Pit Mining Restored Areas." Land 11, no. 2 (January 29, 2022): 212. http://dx.doi.org/10.3390/land11020212.
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Unmanned Aerial Systems, or drones, are very helpful tools for managing open-pit mining operations and developing ecological restoration activities. This article presents a method for identifying water erosion processes in active quarries by means of drone imagery remote sensing, in the absence of pre-existing imagery or mapping for comparison. A Digital Elevation Model (DEM) with a spatial resolution (SR) >10 cm and an orthophoto with an SR >2.5 cm were generated from images captured with a drone and their subsequent photogrammetric processing. By using Geographical Information Systems tools to process the DEM, a detailed drainage network was obtained, the areas of detected water erosion were separated, and the watersheds in the gullies identified. Subsequently, an estimated DEM before the erosive processes was reconstructed by interpolating the gully ridges; this DEM serves as a reference for the relief before the erosion. To calculate the volume of eroded material, the DEM of Differences was calculated, which estimates the volume difference between the previously estimated DEM and the current DEM. Additionally, we calculated the material necessary for the geomorphological adaptation of the quarry and the slope map, which are two valuable factors closely related to the monitoring of erosive processes. The results obtained allowed us to identify the erosion factors quickly and accurately in this type of mining. In the case of water-filled quarries, it would be important to characterize the subsurface relief. Essentially, the presented method can be applied with affordable and non-invasive materials to create digital grid maps at 10 cm resolution, obtaining data ready for 3D metrics, being a very practical landscape modelling tool for characterizing the restoration evolution of open-pit mining spaces.
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Levene, Tamara, Gill Livingston, Sube Banerjee, and Andrew Sommerlad. "Minimum clinically important difference of the Social Functioning in Dementia Scale (SF-DEM): cross-sectional study and Delphi survey." BMJ Open 12, no. 3 (March 2022): e058252. http://dx.doi.org/10.1136/bmjopen-2021-058252.
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ObjectivesGood social functioning is important for people living with dementia and their families. The Social Functioning in Dementia Scale (SF-DEM) is a valid and reliable instrument measuring social functioning in dementia. However the minimum clinically important difference (MCID) has not yet been derived for SF-DEM. This study aims to define the MCID for the SF-DEM.DesignWe used triangulation, incorporating data from a cross-sectional study to calculate the MCID using distribution-based and anchor-based methods, and a Delphi survey.Setting and participantsThe cross-sectional survey comprised 299 family carers of people with dementia. Twenty dementia experts (researchers, clinicians, family carers) rated whether changes on clinical vignettes represented a meaningful change in the Delphi survey.Primary outcome measuresWe calculated the distribution-based MCID as 0.5 of an SD for each of the three SF-DEM domains (1—spending time with others, 2—communicating with others, 3—sensitivity to others). We used the carers’ rating of social functioning to calculate the anchor-based MCID. For the Delphi survey, we defined consensus as ≥75% agreement. Where there was lack of consensus, experts were asked to complete a further survey round.ResultsWe found that 0.5 SD of SF-DEM was 1.9 points, 2.2 and 1.4 points in domains 1, 2 and 3, respectively. Using the anchoring analysis, the MCIDs were 1.7 points, 1.7 points, and 0.9 points in domains 1, 2 and 3, respectively. The Delphi method required two rounds. In the second round, a consensus was reached that a 2-point change was considered significant in all three domains, but no consensus was reached on a 1-point change.ConclusionsBy triangulating all three methods, the SF-DEM’s MCIDs were 1.9, 2.0 and 1.4 points for domains 1, 2 and 3, respectively. For individuals, these values should be rounded to a 2-point change for each domain.
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Tripathi, Anurag, and D. V. Khakhar. "Density difference-driven segregation in a dense granular flow." Journal of Fluid Mechanics 717 (February 1, 2013): 643–69. http://dx.doi.org/10.1017/jfm.2012.603.
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AbstractWe consider the segregation of spheres of equal size and different density flowing over an inclined plane, theoretically and computationally by means of distinct element method (DEM) simulations. In the first part of the work, we study the settling of a single higher-density particle in the flow of otherwise identical particles. We show that the motion of the high-density tracer particle can be understood in terms of the buoyancy and drag forces acting on it. The buoyancy force is given by Archimedes principle, with an effective volume associated with the particle, which depends upon the local packing fraction, $\phi $. The buoyancy arises primarily from normal forces acting on the particle, and tangential forces have a negligible contribution. The drag force on a sphere of diameter $d$ sinking with a velocity $v$ in a granular medium of apparent viscosity $\eta $ is given by a modified Stokes law, ${F}_{d} = c\pi \eta dv$. The coefficient ($c$) is found to decrease with packing fraction. In the second part of the work, we consider the case of binary granular mixtures of particles of the same size but differing in density. A continuum model for segregation is presented, based on the single-particle results. The number fraction profile for the heavy particles at equilibrium is obtained in terms of the effective temperature, defined by a fluctuation–dissipation relation. The model predicts the equilibrium number fraction profiles at different inclination angles and for different mass ratios of the particles, which match the DEM results very well. Finally, a complete model for the theoretical prediction of the flow and number fraction profiles for a mixture of particles of different density is presented, which combines the segregation model with a model for the rheology of mixtures. The model predictions agree quite well with the simulation results.
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Han, Haijiao, Qiming Zeng, and Jian Jiao. "Quality Assessment of TanDEM-X DEMs, SRTM and ASTER GDEM on Selected Chinese Sites." Remote Sensing 13, no. 7 (March 29, 2021): 1304. http://dx.doi.org/10.3390/rs13071304.
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Digital elevation models (DEMs) are the basic data of science and engineering technology research. SRTM and ASTER GDEM are currently widely used global DEMs, and TanDEM-X DEM, released in 2016, has attracted users’ attention due to its unprecedented accuracy. These global datasets are often used for local applications and the quality of DEMs affects the results of applications. Many researchers have assessed and compared the quality of global DEMs on a local scale. To provide some additional insights on quality assessment of 12- and 30-m resolution TanDEM-X DEMs, 30-m resolution ASTER GDEM and 30-m resolution SRTM, this study assessed differences’ performance in relation to not only geographical features but also the ways in which DEMs have been created on selected Chinese sites, taking ICESat/GLAS points with 14-cm absolute vertical accuracy but size of 70-m diameter and 12-m resolution TanDEM-X DEM with less than 10-m absolute vertical accuracy as the reference data for comprehensive quality evaluation. When comparing the three 30-m DEMs with the reference DEM, an improved Least Z-Difference (LZD) method was applied for co-registration between models, and Quantile–Quantile (Q-Q) plot was used to identify if the DEM errors follow a normal distribution to help choose proper statistical indicators accordingly. The results show that: (1) TanDEM-X DEMs have the best overall quality, followed by SRTM. ASTER GDEM has the worst quality. The 12-m TanDEM-X DEM has significant advantages in describing terrain details. (2) The quality of DEM has a strong relationship with slope, aspect and land cover. However, the relationship between aspect and vertical quality weakens after data co-registration. The quality of DEMs gets higher with the increasing number of images used in the fusion process. The quality in where slopes opposite to the radar beam is the worst for SRTM, which could provide a new perspective for quality assessment of SRTM and other DEMs whose incidence angle files are available. (3) Systematic deviations can reduce the vertical quality of DEM. The differences have non-normal distribution even after co-registration. For researchers who want to know the quality of a DEM in order to use it in further applications, they should pay more attention to the terrain factors and land cover in their study areas and the ways in which the DEM has been created.
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Japaridze, Irakli. "Female labor force participation and fertility differentials." Journal of Demographic Economics 85, no. 2 (April 12, 2019): 123–64. http://dx.doi.org/10.1017/dem.2019.1.
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AbstractUS women, on average, had approximately two children in both the 1930s and in the 1970s, yet the fertility distribution in the 1930s was less concentrated. This implies change in reproductive behavior, which cannot be captured by models focusing on average fertility. To explain these changes, I have developed a model that makes a distinction between sons and daughters. In this model, the female labor force participation rate is the probability of each girl becoming an employed woman. This endogenizes the empirically observed difference in the propensity for an all-girl household to have another child compared to an all-boy household, generating large fertility differentials at low participation rates. Higher participation rates raise the expected return from an additional child, as well as the expected return from existing daughters. The first effect tends to increase fertility, while the second effect, for relatively concave utility functions, tends to decrease it, so that the distribution of completed fertilities becomes more concentrated.
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Berman, Eli, and Zaur Rzakhanov. "Fertility, migration, and altruism." Journal of Demographic Economics 86, no. 3 (September 2020): 367–402. http://dx.doi.org/10.1017/dem.2020.18.
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AbstractMigration is a human capital investment in which parents bear costs and children share returns. Therefore, migrants from a population with heterogeneous intergenerational discount rates will self-select on intergenerational altruism. Intergenerational altruism and fertility are arguably linked, therefore immigrants might self-select on eventual fertility. Soviet Jews who migrated to Israel despite high migration costs averaged almost one child more than members of the same birth cohorts who migrated later, at lower cost. Distinguishing selection from treatment effects using mothers' age at migration, selection accounts for most of that difference (the proportion varies with specification), even with controls for religion and religiosity. Selection on fertility may have other explanations, including cultural preservation. To probe, we conduct an alternative empirical test of immigrant selection on altruism, finding that U.S. immigrants spend more time with grandchildren than do natives. Additionally, immigrant self-selection on fertility provides an alternative explanation for Chiswick's (1978, Journal of Political Economy86(5), 897–921) earnings-overtaking result.
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Alcaras, E., P. P. Amoroso, F. G. Figliomeni, C. Parente, and G. Prezioso. "ACCURACY EVALUATION OF COASTLINE EXTRACTION METHODS IN REMOTE SENSING: A SMART PROCEDURE FOR SENTINEL-2 IMAGES." International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLVIII-4/W3-2022 (December 2, 2022): 13–19. http://dx.doi.org/10.5194/isprs-archives-xlviii-4-w3-2022-13-2022.
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Abstract. Different algorithms are available in literature to extract coastline from remotely sensed images and different approaches can be adopted to evaluate the result accuracy. In every case, a reference coastline is suitable to compare alternative solutions: usually, the visual photointerpretation on the RGB composition of the considered imagery and the manually vectorization of the coastline allow an accurate term of comparison, but they are laborious and time consuming. This article aims to demonstrate that a smart procedure is possible using a LiDAR-generated Digital Elevation Model (Lg-DEM) as a useful source from which to rapidly extract the reference coastline. The experiments are carried out on Sentinel-2 imagery, using six indices: Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), Modified Normalized Difference Water Index (MNDWI), Enhanced Vegetation Index (EVI), Red-Green Ratio (RGR) and NIR-Red Ratio (NRR). The unsupervised classification algorithm named K-Means transforms each index resulting product in two clusters, i.e. water and no-water, while the automatic vectorization allows to detect the coastline as separation between land and sea. The coastline from Lg-DEM and the manually achieved one using photointerpretation are both assumed as references for testing result accuracy. In every case, the performance analysis of the six indices products induces similar results, confirming the combination of NDWI and K-Means as the most performing approach. The tests demonstrate that, when Lg-DEM and satellite images concern the same area in the same period or in absence of variations, the coastline extracted from Lg-DEM is useful as reference to compare various methods.
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Li, Qinghua, and Jie Shan. "Georeferencing with Self-Calibration for Airborne Full-Waveform Lidar Data Using Digital Elevation Model." Photogrammetric Engineering & Remote Sensing 87, no. 1 (January 1, 2021): 43–52. http://dx.doi.org/10.14358/pers.87.1.43.
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Precise georeferencing of airborne full-waveform lidar is a complex process. On one hand, no ground control points are visible due to heavy canopy. While on the other hand, precise georeferencing relies on ground control. As an alternative, we propose to use an available digital elevation model (DEM ) as control. The mathematical framework minimizes the difference between the lidar DEM and the reference DEM. Our solution consists of two steps: initial optimization to find reliable ground points through iterative filtering and georeferencing, and fine optimization to achieve precise georeferencing and lidar system calibration. Through this approach, the wave-form-derived DEM can best fit the reference DEM, with a mean of 0.937 m and standard deviation of 0.792 m, while the time-synchronization offset and boresight angles are simultaneously determined, i.e., self-calibrated. This development provides a novel georeferencing approach with self-calibration for lidar data without using conventional ground control points.
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Gallier, Stany, Elisabeth Lemaire, François Peters, and Laurent Lobry. "Rheology of sheared suspensions of rough frictional particles." Journal of Fluid Mechanics 757 (September 23, 2014): 514–49. http://dx.doi.org/10.1017/jfm.2014.507.
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AbstractThis paper presents three-dimensional numerical simulations of non-Brownian concentrated suspensions in a Couette flow at zero Reynolds number using a fictitious domain method. Contacts between particles are modelled using a discrete element method (DEM)-like approach, which allows for a more physical description, including roughness and friction. This work emphasizes the effect of friction between particles and its role on rheological properties, especially on normal stress differences. Friction is shown to notably increase viscosity and second normal stress difference $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}|N_2|$ and decrease $|N_1|$, in better agreement with experiments. The hydrodynamic and contact contributions to the overall particle stress are particularly investigated. This shows that the effect of friction is mostly due to the additional contact stress since the hydrodynamic stress remains unaffected by friction. Simulation results are also compared with experiments, such as normal stresses or effective friction coefficient $\mu (I_v)$, and the agreement is improved when friction is accounted for. This suggests that friction is operative in actual suspensions.
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Knepper, Jennifer, and Bernhard Peuckert. "Anwendung einer +3-Brille bei frühkindlichem Sehscreening mit dem PlusOptix A12R." Optometry & Contact Lenses 1, no. 2 (August 30, 2021): 73–78. http://dx.doi.org/10.54352/dozv.fejn8438.
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Purpose. The aim of this study was to examine the benefit of +3-glasses as a supplement to the measurement of ob- jective ametropia using the PlusOptix A12R vision screener in children. Material and Methods. Experience from practice and the evaluation of the measurement results with and without the use of the +3-glasses are presented. In addition, a way of interpreting the results in practice is presented. Results. The measurement with both methods was evaluated in 1534 out of 2760 cases. The measurements showed no significant difference (z = -0.250, p = 0.802, r = -0.005), how- ever, showed greater scatter results in the measurement with +3-glasses. If you select the more positive measurement, the mean is shifted by 0.26 dpt (SD = 0.68) towards hyperopia. In addition, a lower scatter result and a significant difference to the measurement without glasses are achieved. This is in pairs between 0 D and 4.75 D, with an average of 0.27 (SD = 0.46), with 261 cases (17 %) differences of 0.75 D or more. Conclusion. If only the measurement with +3-glasses is con- sidered, there is no benefit at first. However, the professional selection between the measured values provides a more re- liable statement about the refractive status, especially about the influence of accommodative compensation of hyperopia. The cost-effective production of the glasses, a high acceptan- ce by the children, the low time required and the additional safety of the results speak for the use of the +3-glasses in early childhood vision screenings. Keywords pediatric optometry, screening, hyperopia, accommodation, +3-glasses
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Parrot, J. F., and C. Ramírez-Núñez. "POSITIVE AND NEGATIVE ROUGHNESS ACCORDING TO LOCAL DIFFERENCES BETWEEN DEM SURFACE AND 3D REFERENCE PLANES." ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences V-3-2021 (June 17, 2021): 159–65. http://dx.doi.org/10.5194/isprs-annals-v-3-2021-159-2021.
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Abstract. The irregularities of the earth’s surface are quantified by means of roughness measurements using Digital Elevation Models (DEM’s). This article presents a roughness measurement method that is based on the calculation of the difference of altitude existing between a plane passing through the centre of a moving window and the altitude of the DEM surface inside this window. This method differs from the measure of the standard deviation and best fit plane, in the sense that it considers all difference values, positives or negatives. The measurement is done in a 3 × 3 or a 5 × 5 moving window and contemplates inside this window the plane which passes through the centre of the window and the highest pixel located in the border or perimeter of this window. According to the 3D configuration of the DEM surface inside the moving window, the sum of all the differences is positive or negative, allowing to discriminate the local morphology independently of the global roughness. The roughness variable which distinguishes negative and positive values allows to classify accurately landscape units such as watersheds, riverbeds, volcanic assemblages as well as landforms associated with tectonic structures.
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Cheng, Xinghua, and Zhilin Li. "Configurational Entropy for Optimizing the Encryption of Digital Elevation Model Based on Chaos System and Linear Prediction." Applied Sciences 11, no. 5 (March 8, 2021): 2402. http://dx.doi.org/10.3390/app11052402.
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A digital elevation model (DEM) digitally records information about terrain variations and has found many applications in different fields of geosciences. To protect such digital information, encryption is one technique. Numerous encryption algorithms have been developed and can be used for DEM. A good encryption algorithm should change both the compositional and configurational information of a DEM in the encryption process. However, current methods do not fully take into full consideration pixel structures when measuring the complexity of an encrypted DEM (e.g., using Shannon entropy and correlation). Therefore, this study first proposes that configurational entropy capturing both compositional and configurational information can be used to optimize encryption from the perspective of the Second Law of Thermodynamics. Subsequently, an encryption algorithm based on the integration of the chaos system and linear prediction is designed, where the one with the maximum absolute configurational entropy difference compared to the original DEM is selected. Two experimental DEMs are encrypted for 10 times. The experimental results and security analysis show that the proposed algorithm is effective and that configurational entropy can help optimize the encryption and can provide guidelines for evaluating the encrypted DEM.
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Zhao, S., S. Zhang, and W. Cheng. "RELATIVE ERROR EVALUATION TO TYPICAL OPEN GLOBAL DEM DATASETS IN SHANXI PLATEAU OF CHINA." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-3 (April 30, 2018): 2395–99. http://dx.doi.org/10.5194/isprs-archives-xlii-3-2395-2018.
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Produced by radar data or stereo remote sensing image pairs, global DEM datasets are one of the most important types for DEM data. Relative error relates to surface quality created by DEM data, so it relates to geomorphology and hydrologic applications using DEM data. Taking Shanxi Plateau of China as the study area, this research evaluated the relative error to typical open global DEM datasets including Shuttle Radar Terrain Mission (SRTM) data with 1 arc second resolution (SRTM1), SRTM data with 3 arc second resolution (SRTM3), ASTER global DEM data in the second version (GDEM-v2) and ALOS world 3D-30m (AW3D) data. Through process and selection, more than 300,000 ICESat/GLA14 points were used as the GCP data, and the vertical error was computed and compared among four typical global DEM datasets. Then, more than 2,600,000 ICESat/GLA14 point pairs were acquired using the distance threshold between 100 m and 500 m. Meanwhile, the horizontal distance between every point pair was computed, so the relative error was achieved using slope values based on vertical error difference and the horizontal distance of the point pairs. Finally, false slope ratio (FSR) index was computed through analyzing the difference between DEM and ICESat/GLA14 values for every point pair. Both relative error and FSR index were categorically compared for the four DEM datasets under different slope classes. Research results show: Overall, AW3D has the lowest relative error values in mean error, mean absolute error, root mean square error and standard deviation error; then the SRTM1 data, its values are a little higher than AW3D data; the SRTM3 and GDEM-v2 data have the highest relative error values, and the values for the two datasets are similar. Considering different slope conditions, all the four DEM data have better performance in flat areas but worse performance in sloping regions; AW3D has the best performance in all the slope classes, a litter better than SRTM1; with slope increasing, the relative error for the SRTM3 data increases faster than other DEM datasets; so SRTM3 is better than GDEM-v2 in flat regions but worse in sloping regions. As to FSR value, AW3D has the lowest value, 4.37 %; then SRTM1 data, 5.80 %, similar to AW3D data; SRTM3 has higher value, about 8.27 %; GDEM-v2 data has the highest FSR value, about 12.15 %. FSR can represent the performance of correctly creating the earth surface based on DEM data. Hence, AW3D has the best performance, which is approximate to but a little better than SRTM1. The performance of SRTM3 and GDEM-v2 is similar, which is much worse than AW3D and SRTM1, and the performance of GDEM-v2 is the worst of all. Originated from the DEM dataset with 5m resolution, AW3D is regarded as the most precise global DEM datasets up to now, so it may exerts more effect in topographic analysis and geographic research. Through analysis and comparison of the relative error for the four open global DEM datasets, this research will provide reference in open global DEM datasets selection and applications in geosciences and other relevant fields.
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Stark, Oded, and Krzysztof Szczygielski. "The likelihood of divorce and the riskiness of financial decisions." Journal of Demographic Economics 85, no. 3 (August 22, 2019): 209–29. http://dx.doi.org/10.1017/dem.2019.8.
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AbstractWe link causally the riskiness of men's management of their finances with the probability of their experiencing a divorce. Our point of departure is that when comparing single men to married men, the former manage their finances in a more aggressive (that is, riskier) manner. Assuming that single men believe that low relative wealth has a negative effect on their standing in the marriage market and that they care about their standing in that market more than married men do, we find that a stronger distaste for low relative wealth translates into reduced relative risk aversion and, consequently, into riskier financial behavior. With this relationship in place we show how this difference varies depending on the “background” likelihood of divorce and, hence, on the likelihood of re-entry into the marriage market: married men in environments that are more prone to divorce exhibit risk-taking behavior that is more similar to that of single men than married men in environments that are little prone to divorce. We offer a theoretical contribution that helps inform and interpret empirical observations and regularities and can serve as a guide for follow-up empirical work, having established and identified the direction of causality.
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Hai, G., H. Xie, J. Chen, L. Chen, R. Li, and X. Tong. "EXPERIMENTAL DEM EXTRACTION FROM ASTER STEREO PAIRS AND 3D REGISTRATION BASED ON ICESAT LASER ALTIMETRY DATA IN UPSTREAM AREA OF LAMBERT GLACIER, ANTARCTICA." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-2/W7 (September 14, 2017): 1517–20. http://dx.doi.org/10.5194/isprs-archives-xlii-2-w7-1517-2017.
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DEM Extraction from ASTER stereo pairs and three-dimensional registration by reference to ICESat laser altimetry data are carried out in upstream area of Lambert Glacier, East Antarctica. Since the study area is located in inland of East Antarctica where few textures exist, registration between DEM and ICESat data is performed. Firstly, the ASTER DEM generation is based on rational function model (RFM) and the procedure includes: a) rational polynomial coefficient (RPC) computation from ASTER metadata, b) L1A image product de-noise and destriping, c) local histogram equalization and matching, d) artificial collection of tie points and bundle adjustment, and e) coarse-to-fine hierarchical matching of five levels and grid matching. The matching results are filtered semi-automatically. Hereafter, DEM is interpolated using spline method with ground points converted from matching points. Secondly, the generated ASTER DEM is registered to ICESat data in three-dimensional space after Least-squares rigid transformation using singular value decomposition (SVD). The process is stated as: a) correspondence selection of terrain feature points from ICESat and DEM profiles, b) rigid transformation of generated ASTER DEM using selected feature correspondences based on least squares technique. The registration shows a good result that the elevation difference between DEM and ICESat data is low with a mean value less than 2 meters and the standard deviation around 7 meters. This DEM is generated and specially registered in Antarctic typical region without obvious ground rock control points and serves as true terrain input for further radar altimetry simulation.
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Fu, B. L., Y. Li, E. T. Gao, D. L. Fan, and P. Q. Lou. "STUDY ON ACCURACY ASSESSMENT OF DEM IN THE MARSH USING WITH INTERFEROMETRIC PALSAR, SENTINEL-1A AND TERRASAR-X IMAGES." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-3/W10 (February 7, 2020): 289–96. http://dx.doi.org/10.5194/isprs-archives-xlii-3-w10-289-2020.
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Abstract. To conserve and manage wetland resources, it is important to monitor hydro-geomorphic condition. In this paper, the interferometric SAR images of L-band ALOS-1 PALSAR, C-band Sentinel-1A and X-band TerraSAR were selected to produce DEM of wetland area in the Honghe National Nature Reserve using the InSAR technique. 111 testing points randomly selected from the 1:10000 topographic map were utilized to evaluate accuracy of remote-sensing based DEM. Finally, the interference coherence difference of wetland vegetation among three different wavelengths was compared and analyzed. The results showed that The DEM of wetland area produced by L-band ALOS-1 PALSAR interferometric images was in good agreement with the 1:10,000 topographic map data. The elevation value with the difference less than 3 meters account for over 76% of all testing points. The coherence coefficient of wetland calculated from PALSAR images was higher than Sentinel-1A and TerraSAR images. The coherence coefficient among wetland vegetation types was significantly different. The distribution area of forest and shrub-grass vegetation had a larger coherence coefficient than shallow-water marsh vegetation area and deep-water marsh vegetation area.
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Testut, Laurent, Rachael Hurd, Richard Coleman, Frédérique Rémy, and Benoît Legrésy. "Comparison between computed balance velocities and GPS measurements in the Lambert Glacier basin, East Antarctica." Annals of Glaciology 37 (2003): 337–43. http://dx.doi.org/10.3189/172756403781815672.
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AbstractComparisons between computed balance velocities, obtained from two different computing schemes, and global positioning system (GPS)-derived velocities were made in the Lambert Glacier basin region, East Antarctica. The two computing schemes used for the balance-velocity computations (a flowline (FL) scheme (Remy and Minster, 1993) and a finite-difference (BW) scheme (Budd and Warner, 1996; Fricker and others, 2000)) were first evaluated and compared. One of the key issues studied was the spatial resolution of the digital elevation model (DEM), representing the surface topography of the ice sheet, and the sensitivity of the balance velocities to the length of smoothing applied to the DEM. Comparison with the GPS velocities validated the two schemes to within 5–25% but showed the high sensitivity of the flowline method to the length scale of the smoothing. The finite-difference scheme was found to be robust to the chosen smoothing scale, but the balance-velocity values increased when a finer-resolution DEM was used. Both FL and BW computing schemes tended to overestimate the balance velocities in comparison with the GPS values; some of this discrepancy can be attributed to ice-sheet sliding.
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Fan, Yubin, Chang-Qing Ke, and Xiaoyi Shen. "A new Greenland digital elevation model derived from ICESat-2 during 2018–2019." Earth System Science Data 14, no. 2 (February 21, 2022): 781–94. http://dx.doi.org/10.5194/essd-14-781-2022.
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Abstract. Greenland digital elevation models (DEMs) are indispensable to fieldwork, ice velocity calculations, and mass change estimations. Previous DEMs have provided reasonable estimations for all of Greenland, but the time span of applied source data may lead to mass change estimation bias. To provide a DEM with a specific time stamp, we applied approximately 5.8×108 ICESat-2 observations from November 2018 to November 2019 to generate a new DEM, including the ice sheet and glaciers in peripheral Greenland. A spatiotemporal model fit process was performed at 500 m, 1 km, 2 km, and 5 km grid cells separately, and the final DEM was posted at the modal resolution of 500 m. A total of 98 % of the grids were obtained by the model fit, and the remaining DEM gaps were estimated via the ordinary Kriging interpolation method. Compared with IceBridge mission data acquired by the Airborne Topographic Mapper (ATM) lidar system, the ICESat-2 DEM was estimated to have a maximum median difference of −0.48 m. The performance of the grids obtained by model fit and interpolation was similar, both of which agreed well with the IceBridge data. DEM uncertainty rises in regions of low latitude and high slope or roughness. Furthermore, the ICESat-2 DEM showed significant accuracy improvements compared with other altimeter-derived DEMs, and the accuracy was comparable to those derived from stereophotogrammetry and interferometry. Overall, the ICESat-2 DEM showed excellent accuracy stability under various topographic conditions, which can provide a specific time-stamped DEM with high accuracy that will be useful to study Greenland elevation and mass balance changes. The Greenland DEM and its uncertainty are available at https://doi.org/10.11888/Geogra.tpdc.271336 (Fan et al., 2021).
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Alatas, Masrur, Maria Theresia Sri Budiastuti, Totok Gunawan, Prabang Setyono, Juris Burlakovs, and Erkata Yandri. "The Identification of Micro-hydro Power Plants Potential in Irrigation Areas Based on Unmanned Air Vehicle (UAV) Image Processing." E3S Web of Conferences 190 (2020): 00024. http://dx.doi.org/10.1051/e3sconf/202019000024.
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Estimation of the energy demand in Indonesia will increase by 8.15 % annually until 2030. Indonesia is committed to preventing climate change through mix energy (new and renewable energy). One of the sources of this energy is waterpower plants with a potential of 75 091 MW have been utilized 6.4 %, mini-hydro, and micro-hydro with a potential of 19 385 MW have been utilized 1 %. In the Industrial Revolution 4.0, it is doable to identify such potential using drone. This study was conducted in the Kalibawang irrigation area, Special Region of Yogyakarta, Indonesia. The procedure starts with the generation of detailed Aerial Photography using Drone DJI Phantom 4. The images from aerial photography were then processed into high-resolution Digital Elevation Model (DEM). DEM data represent the study area topography and can be used to identify the stream gradient potential or height difference (H). Six potential points were identified with height differences between 3 m to 8 m, resulting in the potential generated power ranging from 125 kW to 334 kW. This study demonstrates the identification of micro-hydro energy potential points, height difference, and generated power using Drone. Six points were identified with total potential energy 1 418 kW.
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Ajayi, Oluibukun Gbenga, and Mark Palmer. "Modelling 3D Topography by Comparing Airborne Lidar Data with Unmanned Aerial System (UAS) Photogrammetry Under Multiple Imaging Conditions." Geoplanning: Journal of Geomatics and Planning 6, no. 2 (April 7, 2020): 122–38. http://dx.doi.org/10.14710/geoplanning.6.2.122-138.
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This study presents the effect of image data sources on the topographic modelling of part of the National Trust site located at Weston-Super-Mare, Bristol, United Kingdom, covering an approximate area of 1.82 hectares. The accuracy of the DEM generated from 1m resolution and 2m resolution LiDAR data together with the accuracy of the DEM generated from the UAV images acquired at different altitudes are analysed using the 1 m LiDAR DEM as reference for the accuracy assessment. Using the NSSDA methodology, the horizontal and vertical accuracy of the DEMs generated from each of the four sources were computed while the paired sample t-test was conducted to ascertain the existence of statistically significant difference between the means of the X, Y, and Z coordinates of the check points. The result obtained shows that with a RMSE of -0.0101499 and horizontal accuracy of -0.175674686m, the planimetric coordinates extracted from 2 m LiDAR DEM were more accurate than the planimetric coordinates extracted from the UAV based DEMs while the UAV based DEMs proved to be more accurate than the 2m LiDAR DEM in terms of altimetric coordinates, though the DEM generated from UAV images acquired at 50 m altitude gave the most accurate result when compared with the vertical accuracy obtained from the DEM generated from UAV images acquired at 30 m and 70 m flight heights. These findings are also consistent with the result of the statistical analysis at 95% confidence interval.
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Liebsch, Burkard. "Die Frage nach dem Anderen zwischen Ethik und Politik der Differenz: eine vorläufige Bilanz." Phänomenologische Forschungen 2005, no. 1 (2005): 193–220. http://dx.doi.org/10.28937/1000107918.
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This paper critically examines the notion of the other as it emerges in ethics and in the so called politics of difference. The author confronts this notion with social-ontological and dialogistic thematizations of otherness. On that basis a radical revision of what ‚difference‘ means is claimed to be neccessary in ethical and political respect.
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Zhang, Yifan, and Wenhao Yu. "Comparison of DEM Super-Resolution Methods Based on Interpolation and Neural Networks." Sensors 22, no. 3 (January 19, 2022): 745. http://dx.doi.org/10.3390/s22030745.
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High-resolution digital elevation models (DEMs) play a critical role in geospatial databases, which can be applied to many terrain-related studies such as facility siting, hydrological analysis, and urban design. However, due to the limitation of precision of equipment, there are big gaps to collect high-resolution DEM data. A practical idea is to recover high-resolution DEMs from easily obtained low-resolution DEMs, and this process is termed DEM super-resolution (SR). However, traditional DEM SR methods (e.g., bicubic interpolation) tend to over-smooth high-frequency regions on account of the operation of averaging local variations. With the recent development of machine learning, image SR methods have made great progress. Nevertheless, due to the complexity of terrain characters (e.g., peak and valley) and the huge difference between elevation field and image RGB (Red, Green, and Blue) value field, there are few works that apply image SR methods to the task of DEM SR. Therefore, this paper investigates the question of whether the state-of-the-art image SR methods are appropriate for DEM SR. More specifically, the traditional interpolation method and three excellent SR methods based on neural networks are chosen for comparison. Experimental results suggest that SRGAN (Super-Resolution with Generative Adversarial Network) presents the best performance on accuracy evaluation over a series of DEM SR experiments.