Dissertationen zum Thema „Water Remote sensing“

The European Union (EU) has openly solicited advice on the development of EU bathing water quality policy and made calls for the development of remotely sensed operational real world solutions. This research demonstrates a new approach to estimating water quality using remote sensing and specifically to monitoring bathing water quality by using remote sensing to "flag" failing areas for manual survey. This method meets the environmental demands of the EU, the tourist industry, the water industry and environmental monitoring agencies throughout the world. The results show the genuine potential for a remotely sensed monitoring system that could, with further research, lead to an efficient and effective method of monitoring bathing water quality. These findings are particularly important given the imminent changes in EU Bathing Water policy, an expected increase in monitoring costs (currently estimated by the EU to be 15 million euros for 2001 (EU, 2002)) and the widespread availability of airborne sensors and satellites. Simultaneous water quality and spectral data were collected at Southend-on-Sea pier with a Natural Environment Research Council (NERC) loaned spectroradiometer and water sampling equipment. Simultaneous data enabled the accurate analysis of the relationship between water quality and reflectance, avoiding the normal delays experienced with flown or satellite data. The thesis successfully proposes and investigates a remotely sensed flagging system for bathing water quality monitoring using both statistical and visual analysis to identify optimum wavelengths which identify threshold levels of E.coli, suspended sediments, low pH, nitrates, chlorophyll, faecal coliform and temperature. The findings demonstrate that remote sensing could be used to monitor several of the water quality parameters that are relevant to the EU Bathing Water Directives and, in particular, the monitoring of effluent in bathing waters through the successful identification of high E.coli counts. Through the creation and integration of a localised water quality model, it demonstrates that it is possible to predict when water quality parameters exceed a threshold level through direct remote sensing or through the use of remotely sensed indirect water quality parameters. The success rate of remotely sensed "flagging" of samples above a threshold level was tested and used to yield a "predictor" rating for each parameter. Finally, a spectral physical model was constructed that identifies the parameters, wavelengths and secondary parameters that could be used to flag failing water quality areas. This model could be used to improve monitoring coverage and reduce overall costs. The application of the model, which was based on Case 2 coastal water, to other types of coastal area is suggested as needing further research before it could be widely exploited. Remote sensing information could lead to a greater understanding of the coastal environment and offers potential near real time monitoring, allowing for the first time reactive management of coastal water quality in failing water quality areas. This would provide a solution to many of the issues raised by the EU regarding the current bathing water quality directives and provides the remote sensing community with a practical solution to a real world problem.

An experiment was conducted to determine whether the water depth (above soil) and soil type would have any influence on the multispectral reflectances of paddy rice, and their calculated vegetation index values. The results showed that, when vegetation cover was low (below 600 grams of dry biomass per square meter), the near infrared (NIR) reflectances decreased very little with water depth. The same was true for red reflectances, but to a lesser degree. Overall the changes were not significant at 0.05 level of significance when the water depth was increased from 2.5 centimeters to 10 centimeters. When the vegetation cover became higher most NIR and red reflectances did not show a significant decrease with the increase of the water depth, and sometimes they even increased slightly up to a water depth of 6.4 cm. Nevertheless both rice cover and water depth as well as soils played an important role in the reflectance pattern in red and NIR bands. Some index values increased and some decreased depending on water depth and rice cover. Statistical analysis of the data showed that rice multispectral responses were mainly controlled by vegetation and minimally influenced by soil and water depths.

The development of techniques for the detection of water leaks from underground pipelines is seen as a high profile activity by water companies and regulators. This is due to increasing water demands and problems with current leak detection methods. In this thesis optical reflectance and microwave backscatter were used to identify optimal indices for detecting water leaks amongst a variety of different land cover types at different growth stages. Ground-based surveys and modelling techniques were used to establish optimal wavelengths for detection. Results from these studies suggested that in the optical domain visible/middle infrared ratios show potential for leak detection for a wide range of leak types, under a variety of vegetation canopies at different growth stages. Given the sensitivity of L-band radar to moisture, and the ability to separate contributions from canopy and ground surface, it is possible to detect surface water beneath a range of vegetation canopies. The optimal leak detection indices were then used to idenitfy leaks on airborne image data. The available image data was L - band fully polarimetric E-SAR data, and 126 channel HYMAP hyperspectral airborne data which were acquired over an 8km section of the Vrynwy aqueduct (UK), which included a high concentration of leaks. Four of the five leaks were identifiable on the optical image data and none of the leaks were detectable on the microwave data. However the E-SAR data was obtained under unfavourable conditions. The results of both approaches are used to infer limits of detection in terms of season and meteorological conditions for a range of land covers. Preliminary findings suggest that leaks may be optimally detected when canopy height is low, surrounding soil is dry after a period of no rain, and the leak has been present for at least 2 days. The results from this work suggest that remote sensing is both an effective and feasible tool for leak identification.

I aim to determine whether or not remote sensing, through multispectral, satellite and digital photography, is a feasible and accurate method for determining drought stress in Fynbos vegetation. I hypothesize that (1) water stress in fynbos is detectable with the use of a remote sensing index, namely NDVI and (2) that the remotely sensed trends will correlate with ground truth measures of water stress.

Techniques are developed for the visual interpretation of drainage features from satellite imagery. The process of interpretation is formalised by the introduction of objective criteria. Problems of assessing the accuracy of maps are recognized, and a method is developed for quantifying the correctness of an interpretation, in which the more important features are given an appropriate weight. A study was made of imagery from a variety of landscapes in Britain and overseas, from which maps of drainage networks were drawn. The accuracy of the mapping was assessed in absolute terms, and also in relation to the geomorphic parameters used in hydrologic models. Results are presented relating the accuracy of interpretation to image quality, subjectivity and the effects of topography. It is concluded that the visual interpretation of satellite imagery gives maps of sufficient accuracy for the preliminary assessment of water resources, and for the estimation of geomorphic parameters. An examination is made of the use of remotely sensed data in hydrologic models. It is proposed that the spectral properties of a scene are holistic, and are therefore more efficient than conventional catchment characteristics. Key hydrologic parameters were identified, and were estimated from streamflow records. The correlation between hydrologic variables and spectral characteristics was examined, and regression models for streamflow were developed, based solely on spectral data. Regression models were also developed using conventional catchment characteristics, whose values were estimated using satellite imagery. It was concluded that models based primarily on variables derived from remotely sensed data give results which are as good as, or better than, models using conventional map data. The holistic properties of remotely sensed data are realised only in undeveloped areas. In developed areas an assessment of current land-use is a more useful indication of hydrologic response.

Shallow lakes are an important ecological and socio-economic resource. However, the impact of human pressures, both at the lake and catchment scale, has precipitated a decline in the ecological status of many shallow lakes, both in the UK, and throughout Europe. There is now, as direct consequence, unprecedented interest in the assessment and monitoring of ecological status and trajectory in shallow lakes, not least in response to the European Union Water Framework Directive (2000/60/EC). In this context, the spatially-resolving and panoramic data provided by remote sensing platforms may be of immense value in the construction of effective and efficient strategies for the assessment and monitoring of ecological status in shallow lakes and, moreover, in providing new, spatially-explicit, insights into the function of these ecosystems and how they respond to change. This thesis examined the use of remote sensing data for the assessment of (i) phytoplankton abundance and species composition and (ii) aquatic vegetation distribution and ecophysiological status in shallow lakes with a view to establishing the credence of such an approach and its value in limnological research and monitoring activities. High resolution in-situ and airborne remote sensing data was collected during a 2-year sampling campaign in the shallow lakes of the Norfolk Broads. It was demonstrated that semi-empirical algorithms could be formulated and used to provide accurate and robust estimations of the concentration of chlorophyll-a, even in these optically-complex waters. It was further shown that it was possible to differentiate and quantify the abundance of cyanobacteria using the biomarker pigment C-phycocyanin. The subsequent calibration of the imagery obtained from the airborne reconnaissance missions permitted the construction of diurnal and seasonal regional-scale time-series of phytoplankton dynamics in the Norfolk Broads. This approach was able to deliver unique spatial insights into the migratory behaviour of a potentially-toxic cyanobacterial bloom. It was further shown that remote sensing can be used to map the distribution of aquatic plants in shallow lakes, importantly including the extent of submerged vegetation, which is central to the assessment of ecological status. This research theme was subsequently extended in an exploration of the use of remote sensing for assessing the ecophysiological response of wetland plants to nutrient enrichment. It was shown that remote sensing metrics could be constructed for the quantification of plant vigour. The extrapolation of these techniques enabled spatial heterogeneity in the ecophysiological response of Phragmites australis to lake nutrient enrichment to be characterised and assisted the formulation of a mechanistic explanation for the variation in reedswamp performance in these shallow lakes. It is therefore argued that the spatially synoptic data provided by remote sensing has much to offer the assessment, monitoring and policing of ecological status in shallow lakes and, in particular, for facilitating the development of pan-European scale lake surveillance capabilities for the Water Framework Directive (2000/60/EC). It is also suggested that remote sensing can make a valuable contribution to furthering ecological understanding and, most significantly, in enabling ecosystem processes and functions to be examined at the lake-scale.

This PhD study focusses on the use of MEdium Resolution Imaging Spectrometer (MERIS) data for reliable and quantitative water-quality assessment of optically-complex waters (lake, brackish and coastal waters). The thesis is divided into two parts: A. intercalibration of reflectance measurements in different optically-complex water bodies (Paper I), and validation of various satellite processing algorithms for the coastal zone (Paper II). B. Applications: the use of MERIS data in integrated coastal zone management mostly using Himmerfjärden bay as an example. Himmerfjärden bay is one of the most frequently monitored coastal areas in the world and it is also the recipient of a large urban sewage treatment plant, where a number of full-scale nutrient management experiments have been conducted to evaluate the ecological changes due to changes in nutrient schemes in the sewage plant. Paper I describes the development and assessment of a new hyperspectral handheld radiometer for in situ sampling and validation of remote sensing reflectance.  The instrument is assessed in comparison with readily available radiometers that are commonly used in validation. Paper II has a focus on the validation of level 2 reflectance and water products derived from MERIS data. It highlights the importance of calibration and validation activities, and the current accuracy and limitations of satellite products in the coastal zone.  Bio-optical in situ data is highlighted as one of the key components for assessing the reliability of current and future satellite missions. Besides suspended particulate matter (SPM), the standard MERIS products have shown to be insufficient to assure data quality retrieval for Baltic Sea waters. Alternative processors and methods such as those assessed and developed in this thesis therefore will have to be put in place in order to secure the success of future operational missions, such as Sentinel-3. The two presented manuscripts in the applied part B of the thesis (paper III and IV), showed examples on the combined use of in situ measurements with optical remote sensing to support water quality monitoring programs by using turbidity and suspended particulate matter as coastal indicators (manuscript III). The article also provides  a new turbidity algorithm for the Baltic Sea and a robust and cost-efficient method for research and management.  A novel approach to improve the quality of the satellite-derived products in the coastal zone was demonstrated in manuscript IV. The analysis included, the correction for adjacency effects from land and an improved pixel quality screening.  The thesis provides the first detailed spatio-temporal description of the evolution of phytoplankton blooms in Himmerfjärden bay  using quality-assured MERIS data, thus forwarding our understanding of ecological processes in in Swedish coastal waters. It must be noted that monitoring from space is not a trivial matter in these optically-complex waters dominated by the absorption of coloured dissolved organic matter (CDOM). These types of coastal waters are especially challenging for quantitative assessment from space due to their low reflectance.  Papers III and IV thus also provide tools for a more versatile use in other coastal waters that are not as optically-complex as the highly absorbing Baltic Sea waters. The benefits of the increased spatial-temporal data coverage by optical remote sensing were presented, and also compared to in situ sampling methods (using chlorophyll-a as indicator).

Research funders:

European Space Agency (ESA, contract no.21524/08/I-OL)

NordForsk funding: Nord AquaRemS Ref. no. 80106

NordForsk funding:  NordBaltRemS Ref.no. 42041

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

The Pioneer Venus Orbiter Infrared Radiometer and Venera 15 Fourier Transform Spectrometer observations of thermal emission from Venus' middle atmosphere between 10°S and 50°N were used to determine global maps of temperature, cloud optical depth and water vapour abundance. The spectral regions observed include the strong 15 μtm carbon dioxide band and the 45 μm fundamental rotational water band. The main aim of this thesis is to reconcile the water vapour abundance results from these two sets of observations reported in previous studies. New radiative transfer and retrieval models have been developed for this purpose based on new correlated-k absorption tables calculated with up-to-date spectral line data. The H₂SO₄ cloud opacity and scattering properties have been recalculated from new refractive index data using Mie theory. For the first time these two sets of observations have been analysed using the same retrieval tools. From the Pioneer Venus Orbiter Infrared Radiometer observations we report a high abundance of water vapour in the early afternoon at the equatorial cloud-top region and a strong day-night variability in the cloud-top pressure. From the Venera 15 Fourier Transform Spectrometer observations we report medium local variability in water vapour abundance, with highest values in the near-equatorial region and slight decrease towards the polar region. It is found that serious constraints are placed on the validation of the retrievals by the lack of adequately accurate H₂SO₄ optical properties data in the shorter wavelengths and by the poor vertical resolution when sensing the complex but interesting cloud region which prohibits its rigorous modelling. The proposed European Space Agency Venus Express mission will carry a number of high resolution infrared and UV instruments that will shed new light to the interesting question of water vapour abundance in Venus' middle atmosphere.

Remote sensing is being used in agriculture for crop management. Ground based remote sensing data acquisition system was used for collection of high spatial and temporal resolution data for irrigated broccoli crop. The system was composed of a small cart that ran back and forth on a rail system that was mounted on a linear move irrigation system. The cart was equipped with a sensor that had 4 discrete wavelengths; 550 nm, 660 nm, 720 nm, and 810 nm, and an infrared thermometer, all had 10 nm bandwidth. A global positioning system was used to indicate the cart position. The study consisted of two parts; the first was to evaluate remotely sensed reflectance and indices in broccoli during the growing season, and determine whether remotely sensed indices or standard deviation of indices can distinguish between nitrogen and water stress in broccoli, and the second part of the study was to evaluate remotely sensed indices and standard deviation of remotely sensed indices in broccoli during daily changes in solar zenith angle. Results indicated that nitrogen was detected using Ratio Vegetation index, RVI, Normalized Difference Vegetation Index, NDVI, Canopy Chlorophyll Concentration Index, CCCI, and also using the reflectance in the Near-Infrared, NIR, bands. The Red reflectance band capability of showing stress was not as clear as the previous indices and bands reflectance. The Canopy Chlorophyll Concentration Index, CCCI, was the most successful index. The Crop Water Stress Index was able to detect water stress but it was highly affected by the solar zenith angle change along the day.

Remote sensing has the potential to monitor spatial variation in water quality over large areas. While ocean colour work has developed analytical bio-optical water quality retrieval algorithms for medium spatial resolution platforms, remote sensing of lake water is often limited to high spatial resolution satellites such as Landsat, which have limited spectral resolution. This thesis presents the results of an investigation into satellite monitoring of lake water quality. The aim of this investigation was to ascertain the feasibility of estimating water quality and its spatial distribution using Landsat 7 ETM+ imagery combined with in situ data from Rotorua and Waikato lakes. For the comparatively deep Rotorua lakes, r² values of 0.91 (January 2002) and 0.83 (March 2002) were found between in situ chlorophyll (chl) a and the Band1/Band3 ratio. This technique proved useful for analysing the spatial distribution of phytoplankton, especially in lakes Rotoiti and Rotoehu. For the more bio-optically complex shallow lakes of the Waikato, a linear spectral unmixing (LSU) approach was investigated where the water surface reflectance spectrum is defined by the contribution from pure pixels or endmembers. The model estimates the percentage of the endmember within the pixel, which is then used in a final regression with in situ data to map water quality in all pixels. This approach was used to estimate the concentration of chl a (r² = 0.84). Total suspended solid (TSS) concentration was mapped using the traditional Band 3 regression with in situ data, which combined atmospherically corrected reflectance for both images into a single relationship (r² = 0.98). The time difference between in situ data collection and satellite data capture is a potential source of error. Other potential sources of error include sample location accuracy, the influence of dissolved organic matter, and masking of chl a signatures by high concentrations of TSS. The results from this investigation suggest that remote sensing of water quality provides meaningful and useful information with a range of applications and could provide information on temporal spatial variability in water quality.

Water vapour is the principle source of opacity at infrared wavelengths in the Earth’s atmosphere. In support of site testing for the European Extremely Large Telescope (E-ELT), we have used La Silla and Paranal as calibration sites to verify satellite measurements of precipitable water vapour (PWV). We reconstructed the PWV history over both sites by analysing thousands of archived high-resolution echelle calibration spectra and compared that to satellite estimates for the same period. Three PWV measurement campaigns were conducted over both sites using several independent measurement techniques. Radiosondes were launched to coincide with satellite measurements and provide a PWV reference standard allowing intercomparison between the various instruments and methods. This multi-faceted approach has resulted in a unique data set. Integral to this analysis is the internal consistency provided by using a common atmospheric model.
xvii, 206 leaves : ill. (some col.) ; 28 cm

Lake Atitlan in Guatemala is a vital source of drinking water. The deteriorating conditions of water quality in this lake threaten human and ecological health as well as the local and national economy. Given the sporadic and limited measurements available, it is impossible to determine the changing conditions of water quality. The goal of this thesis is to use Hyperion satellite images to measure water quality parameters in Lake Atitlan. For this purpose in situ measurements and satellite-derived reflectance data were analyzed to generate an algorithm that estimated Chlorophyll concentrations. This research provides for the first time a quantitative application of hyperspectral satellite remote sensing for water quality monitoring in Guatemala. This approach is readily transferable to other countries in Central America that face similar issues in the management of their water resources.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 171-191).
Remotely sensed measurements made by radars or radiometers in the low microwave frequency range are sensitive to soil moisture, soil roughness, and vegetation water content. Measurements made at multiple polarizations can be used to determine additional ancillary parameters alongside the primary variable of interest. However, if an attempt is made to retrieve too many parameters from too few measurements, the resulting retrievals will contain high levels of noise. In this thesis, I introduce a framework to determine an upper bound on the number of geophysical parameters that can be retrieved from remotely sensed measurements such as those made by microwave instruments. The principles behind this framework, as well as the framework itself, are then applied to derive two new ecohydrological variables: a) soil moisture profiles across much of the root-zone and b) vegetation optical depth, which is proportional to vegetation water content. For P-band observations, it is shown that soil moisture variations with depth must be accounted for to prevent large forward modeling - and thus retrieval - errors. A Tikhonov regularization approach is then introduced to allow retrieval of soil moisture in several profile layers by using statistics on the expected co-variation between soil moisture at different depths. The algorithm is tested using observations from the NASA Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS) Mission over the Harvard Forest in Western Massachusetts. Additionally, at L-band, a multi-temporal algorithm is introduced to determine vegetation optical depth (VOD) alongside soil moisture. The multi-temporal approach used reduces the chance of compensating errors between the two retrieved parameters (soil moisture and vegetation optical depth), caused by small amounts of measurement noise. In several dry tropical ecosystems, the resulting VOD dataset is shown to have opposite temporal behavior to coincident cross-polarized backscattering coefficients, an active microwave indicator of vegetation water content and scattering. This possibly shows dry season bud-break or enduring litter presence in these regions. Lastly, cross-polarized backscattering coefficients are used to test the hypothesis that vegetation water refilling slows down under drought even at the ecosystem scale. Evidence for this hypothesis is only found in the driest location tested.
by Alexandra Georges Konings.
Ph. D.

Environmental controls are becoming more and more expensive to implement, so environmental management is becoming more technologically advanced and efficient through the adoption of new techniques and models. This paper reviews the potential for storm water runoff for the city of Denton, Texas and with the main objective to perform storm water runoff analyses for three different land use datasets; each landuse dataset created with a different methodology. Also analyzed was the difference between two North Central Texas Council of Governments land use datasets and my own land use dataset as a part of evaluating new and emerging remote sensing techniques. The results showed that new remote sensing techniques can help to continually monitor changes within watersheds by providing more accurate data.

This thesis illustrates the specific aspects that influence or limit the application of remotely-sensed data for information retrieval from coastal marine, estuarine and riverine environments. The thesis is drawn principally from ten separate studies and is divided into discrete sections, or experiments, that provide an understanding of the fundamental aspects of the effects of the atmosphere, water surface, water column and bottom on sensor-received reflected signal.The results show the importance of precise calculation of acquisition parameters and the absolute importance of relevant reference data. Most instrumentation for remote sensing at visible wavelengths has been developed for terrestrial applications where signal is rarely limiting and target features are relatively static. For in-water applications, where signal is small and noise can be large, the features to be sensed may be temporally dynamic and obscured.However, the work presented also shows the great benefit and spatial cost-effectiveness that can be obtained if the spectral and temporal specification is adequately considered. The prime motivation for such applications usually comes from the requirement to detect and quantify water column characteristics, such as phytoplankton forming as algal blooms, and bottom stratigraphic condition, such as benthic habitat mapping for fishery or conservation purposes.

Sphagnum's strong water-holding capacities, its dominance in bogs, and the overall importance of water in regulating photosynthesis make it a key ecosystem engineer. Though its effectiveness in this context has rarely been tested, Spectral Vegetation Indices (SVIs) derived from hyperspectral data allow for efficient modeling of Sphagnum gravimetric water content over large scales. This study tests whether a linear model relating a SVI to Sphagnum gravimetric water content (i.e. S. capillifolium, S. magellanicum, S. angustifolium/S. fallax, or all Sphagnum species pooled together) can be applied to the landscape level using airborne hyperspectral imagery taken over Mer Bleue Bog, near Ottawa, Ontario, Canada. The depth of a Sphagnum species sample contributing to the reflectance and the vertical distribution of water across a species sample was also analyzed to test the accuracy of water content measurements. Additionally, image SVI data were compared to field SVI data to test the effectiveness of image spectra. Results indicate that light penetrated 1.5 cm in S. capillifolium samples, 1.0 cm in S. magellanicum samples, and 2.5 cm in S. angustifolium/S. fallax samples. Water variability was highest in samples with elevated water contents for every Sphagnum species analyzed. The Normalized Difference Water Index (NDWI) (dimensionless) was the most effective in estimating Sphagnum gravimetric water content of all SVIs (Root Mean Square Error=161.34%, P= 0.000). Image NDWI values mimicked field NDWI values (Root Mean Square Error= 0.000740, P= 0.0000). The application of the NDWI to areas identified as being favorable for Sphagnum growth in an image resulted in a map of Sphagnum gravimetric water content for a given day in a bog.
Le contenu d'eau des sphaignes est important pour le fonctionnement des tourbières ombrotrophes, suite aux fortes capacités de rétention d'eau dans ces espèces, la domination de ses espèces dans les tourbières ombrotrophes, et l'importance d'eau dans la régulation de la photosynthèse. L'efficacité des "Spectral Vegetation Indices" (SVIs) dérivée des données hyperspectrales permet une modélisation efficace du contenu d'eau gravimétrique des sphaignes sur de grands échelons. Cependant, l'efficacité des SVIs dans ce contexte a été rarement examinée. Cette étude examine si un modèle linéaire reliant un SVI au contenu d'eau gravimétrique des sphaignes (i.e. S. capillifolium, S. magellanicum, S. angustifolium/S. fallax, ou tous les espèces Sphagnum jumelées ensemble) peut être appliqué au niveau paysagier en utilisant l'imagerie hyperspectrale aérienne prise au-dessus de la tourbière ombrotrophe Mer Bleue, située à proximité d'Ottawa, en Ontario, au Canada. La profondeur d'un échantillon d'une espèce de Sphagnum qui contribue à la réflectance et la distribution verticale d'eau à travers un échantillon a aussi été analysée pour tester l'exactitude des mesures du contenu d'eau. De plus, les données de SVI générées par les images ont été comparées aux données SVI générées par les mesures prises sur le terrain pour examiner l'efficacité des spectres générées par les images. Les résultats indiquent que la lumière a pénétré à une profondeur de 1.5 cm dans les échantillons de S. capillifolium, 1.0 cm dans les échantillons de S. magellanicum, et 2.5 cm dans les échantillons de S. angustifolium/S. fallax. La variabilité d'eau a été le plus prononcée dans les échantillons avec des contenus d'eaux gravimétriques élevées pour chaque espèce de Sphagnum analysée. La "Normalized Difference Water Index" (NDWI) (sans dimension) a été la plus efficace dans l'estimation du contenu d'eau gravimétrique des espèces de tous les SVIs ("Root Mean Square Error"=161.34%, P= 0.000). Les valeurs de NDWI dérivées du terrain ont été semblabes à celles collectionnées sur le terrain (“Root Mean Square Error”= 0.000740, P= 0.0000). L'application du NDWI aux régions identifiées comme étant favorables pour la croissance des sphaignes dans une image a donné, comme résultat, une carte du contenu d'eau gravimétrique des sphaignes pour une journée dans une tourbière ombrotrophe.

The intention of this investigation is to investigate the various forms of water wave reflection to a high degree of accuracy. Close range photogrammetry is the technique that is used to measure the water surface profile, as it produces an accurate and comprehensive analysis of the water surface profiles. Conventional photogrammetry techniques (photography) were used in preference to near real time photogrammetry (digital). Although near real time photogrammetry has the advantage of a far higher rate of data acquisition, it does not achieve the same degree of accuracy as can be achieved by conventional photogrammetry, the technique finally used for this investigation. For the generation of the desired wave patterns, certain equipment was developed and modified. To test the various angles of incidence a moveable reflecting wall was built. Due to the small size of the wave basin, an efficient wave absorber was required to absorb the reflected wave generated when oblique wave reflection was investigated. It was observed that a very poor quality wave was being generated by the wave generator, as a result of its flexibility. Consequently the wave generator was stiffened considerably which improved the wave generated. Interesting information was obtained from the analysis of the standing wave. A coefficient of reflection of 1,6 at the reflection wall was obtained, this places new emphasis on the relationship between the standing wave and overtopping. The oblique wave reflection resu1ts corresponded well with theoretical predictions, while no well-defined trends were established for the mach wave. The data for the mace wave did however suggest that previously established trends for the mach wave may not be correct. Close range photogrammetry produced accurate results, and is an excellent method for water surface profile measurement. The results obtained showed that the wave generator was not generating a pure wave, which lead to unknown errors in the results of spot heights. Conventional photogrammetry is a slow process, so not enough data was acquired to adequately analyse the reflection trends. This suggests that in order for the trends to be well-established, near real time photogrammetry should be used once these systems have developed sufficient accuracy.

By 2025, the Food and Agriculture Organization of the United Nations predicts that two-thirds of the world population will experience water stress conditions. In addition, it is expected that world population will increase significantly during the following years. Agriculture is the largest consumer of fresh water, estimated 75%. The optimization of its use is therefore crucial for future. The main objective of irrigation scheduling is to guarantee maximum crop yield while saving significant amounts of water. The main difficulty to determine a correct and optimal irrigation scheduling strategy is due to complexity and variability of the Soil-Plant-Atmosphere continuum. In each field site, this continuous SPA has different patterns as a consequence of environmental conditions, crop, soil hydraulic properties and soil tillage. Several tools and methodologies are employed nowadays to monitor an improve irrigation scheduling. However, they all have advantages and limitations, or, each one is used without considering the information provided by the others, simplifying the system and avoiding information. This thesis aims to improve irrigation scheduling by combining different tools available at the present time. This combination aims to answer different kind of questions when irrigation scheduling in a field site must be defined. For this, each tool has been used and supported by others. In addition, this thesis will discuss when and how these tools might be employed. Firstly, we compare different tools and methodologies used to measure water content in an agriculture field. Specifically, we compared gravimetric measurements and water content sensors measurements with DISPATCH algorithm data. This algorithm is one of several algorithms who estimates soil surface water content using remote sensing data. The main goal was determining if remote sensing data can improve water content data measured by sensors. We found that DISPATCH algorithm is no capable to improve water content sensors measurements. Secondly, we present a methodology where a simulation-optimization problem is solved in order to find an optimal irrigation scheduling strategy. This strategy might guarantee the maximum economic net margin. This methodology has been applied in a real field. The optimal irrigation scheduling of this field is compared with the traditional irrigation scheduling method, based water requirements. Results show that even though the traditional method supplies the volume of water evapotranspired, this methodology of scheduling irrigation is not enough to avoid crop water stress, compromising final crop yield. In this case, optimal irrigation strategy improves the final net margin in comparison the traditional method. We demonstrate that depending on soil properties, optimal irrigation scheduling is different. Thirdly, we improved the irrigation scheduling in a field site where irrigation was applied with the same criteria. In this part of the thesis we employed NDVI remote sensing data, water content sensors and simulation models to determine the optimal irrigation. The improvement is based on management zones delineation with NDVI data. In this case, water content sensors are used to define if each management zone presents different water content patterns and to verify that when the field is divided into different management zones there is a gain in terms of water content uniformity. Finally, an optimal irrigation scheduling calendar is proposed to allow the consultants to take within-season irrigation decisions. Results show that management zones are dynamic during the growing season and the optimal irrigation scheduling might also be dynamic. In addition, we found that the uniform irrigation applied in the entire field, without considering the possible differences in soil properties, produced waterlogging in two management zones, therefore, transpiration decreases in comparison to the others.
El 2025 la "Food and Agriculture Organization" de les Nacions Unides prediu que dues terceres parts de la població mundial patirà condicions d'estrés hídric. A més a més, s'espera que la població mundial augmenti els propers anys. L'agricultura és el consumidor principal d'aigua dolça, concretament un 75%. Considerant aquest context, existeix una necessitat important d'optimitzar l'aigua de reg en un futur proper. La programació del reg és l'encarregada de determinar el moment i la quantitat d'aigua que s'ha d'aplicar. El seu objectiu principal és garantir un rendiment màxim del cultiu i a la vegada estalviar aigua. La dificultat principal per determinar l'estratègia de programació de reg correcta i òptima és degut a la complexitat i variabilitat del continu Sòl-Planta-Atmòsfera. Diverses eines i metodologies són emprades avui en dia per monitoritzar i determinar la programació del reg. Malgrat l'àmplia variabilitat de possibilitats, totes elles tenen avantatges i limitacions, o sovint, cada una d'elles és fa servir sense considerar la informació que poden proporcionar les altres, simplificant el sistema i obviant informació. Aquesta tesis vol millorar la programació del reg combinant diferents eines i metodologies que estan disponibles avui en dia. La combinació té com a objectiu satisfer necessitats diferents en el moment que la programación del reg ha de ser definida, destacant les avantatges i minimitzant les limitacions de cada metodologia i eina, així com l'efecte de l'escala. Primerament, hem comparat diferents eines i metodologies per mesurar el contingut d'aigua al sòl en una parcel·la de cultiu. Concretament, s'han comparat mesures gravimètriques i de contingut d'aigua de sensors amb mesures de l'algorisme DISPATCH. Aquest algorisme és un de varis algorismes que estimen el contingut d¿aigua superficial del sòl emprant dades de teledetecció. L'objectiu principal era determinar si les dades de teledetecció poden millorar les dades de contingut d'aigua mesurades pels sensors. El resultats mostren que, ara per ara i considerant les condicions de camp, el DISPATCH no és capaç de millorar les mesures dels sensors de contingut d'aigua al sòl. Després, presentem una metodologia on es soluciona un problema de simulació-optimització per a determinar una estratègia de programació de reg òptim. Aquesta estratègia ha de garantir un rendiment econòmic net màxim. S'ha aplicat en una parcel·la de cultiu real. L'estratègia de programació de reg òptim ha estat comparat amb el mètode tradicional de programació de reg, que està basat amb el càlcul de les necessitats hídriques. Encara que el mètode tradicional reemplaça per complet l'aigua evapotranspirada, els resultats mostren que la manera de repartir l'aigua no evita l'estres hídric del cultiu, disminuint el rendiment. En aquest cas, la programació del reg òptim millora el rendiment econòmic net. Els resultats mostren que depenent el tipus de sol, la programació del reg ha de ser diferent. Finalment, s'ha millorat la programació del reg en una parcel·la de cultiu on el reg s'havia aplicat uniformement en tota la seva extensió. En aquesta part de la tesis, es fan servir dades de teledetecció de NDVI, dades de sensors de contingut d'aigua al sòl i models de simulació per a determinar el reg òptim. La millora està basada en la delineació de zones maneig amb les dades de NDVI. En aquest cas, els sensors s'han emprat per a determinar si casa zona de maneig representa diferents patrons de contingut d'aigua i per a validar si quan la parcel·la és dividida en zones de maneig, la variabilitat disminueix. Finalment, es proposa un calendari de programació de reg òptim per a poder prendre decisions en la campanya de reg. Els resultat mostren que les zones de maneig són dinàmiques així com el reg òptim. A més a més s'ha vist que el reg uniforme produeix asfixia radicular a dues de les zones de maneig, disminueix la transpiració en comparació amb els altres.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001.
Vita.
Includes bibliographical references (leaves 30-31).
The purpose of this study is to estimate land water runoff from satellite measurements of net radiation at the top of the atmosphere by invoking columnar atmospheric water and energy balance. Land water runoff is an important parameter in many areas including management of human water use and validation of climate models. Energy measurements taken by satellite are less prone to error than the river discharge measurements required in conventional land water runoff estimates. Mean annual )and water runoff can be determined from net radiation at the top of the atmosphere and the Divergence Bowen Ratio (DBR). The DBR is the ratio of the horizontal flux of internal and potential energy to the horizontal flux of latent heat in the atmosphere. A tropical DBR of -2 was determined from two independent techniques, from a least squares regression relating net radiation with runoff and from the calculation of DBR from local surface humidity. The DBR of -2 corresponds to an approximately one-to-one relationship between net radiation at the top of the atmosphere and land water runoff in the tropics. This DBR also implies that the horizontal divergence of internal and potential energy is equal to twice the horizontal convergence of latent heat through a vertical atmospheric column in the tropics. These simple relationships do not hold in the higher latitudes. Over the tropics, horizontal and vertical transports of energy and moisture are predominantly by nearsteady air motions. Across middle to high latitudes, transient eddy mechanisms become important and the assumptions of the DBR (horizontal temperature homogeneity and steady circulation) break down.
by Jiganesh Govind Patel.
S.M.

This thesis illustrates the specific aspects that influence or limit the application of remotely-sensed data for information retrieval from coastal marine, estuarine and riverine environments. The thesis is drawn principally from ten separate studies and is divided into discrete sections, or experiments, that provide an understanding of the fundamental aspects of the effects of the atmosphere, water surface, water column and bottom on sensor-received reflected signal.The results show the importance of precise calculation of acquisition parameters and the absolute importance of relevant reference data. Most instrumentation for remote sensing at visible wavelengths has been developed for terrestrial applications where signal is rarely limiting and target features are relatively static. For in-water applications, where signal is small and noise can be large, the features to be sensed may be temporally dynamic and obscured.However, the work presented also shows the great benefit and spatial cost-effectiveness that can be obtained if the spectral and temporal specification is adequately considered. The prime motivation for such applications usually comes from the requirement to detect and quantify water column characteristics, such as phytoplankton forming as algal blooms, and bottom stratigraphic condition, such as benthic habitat mapping for fishery or conservation purposes.

Snow is a key component of the Earth’s energy balance, climate, environment, and a major source of freshwater in many regions. Seasonal and perennial snow cover affect up to 50% of the Northern Hemisphere landmass, which accounts for vast regions of the Earth that influence climate, culture, and commerce significantly. Information on snow properties such as snow cover, depth, and wetness is important for making hydrological forecasts, monitoring climate change, weather prediction, and issuing snowmelt runoff, flash flood, and avalanche warnings. Hence, adequate knowledge of the areal extent of snow and its properties is essential for hydrologists, water resources managers, and decision-makers.

The use of infrared (IR) and microwave (MW) remote sensing (RS) has demonstrated the capability of estimating the presence of snow cover and snowpack properties with accuracy. However, there are few publicly accessible, operational RS-based snow depth products, and these only provide the depth of recently accumulated dry snow because retrievals lose accuracy drastically for wet snow (late winter - early spring). Furthermore, it is common practice to assume snow grain size and wetness to be constant to retrieve certain snow properties (e.g. snow depth). This approach is incorrect because these properties are space- and time- dependent, and largely impact the MW signal scattering. Moreover, the remaining operational snow depth products have not been validated against in-situ observations; which is detrimental to their performance and future calibrations.

This study is focused on the discovery of patterns in geospatial data sets using data mining techniques for mapping snow depth globally at 10 km spatial resolution. A methodology to develop a RS MW-based snow depth and water equivalent (SWE) product using regression tree algorithms is developed. The work divided into four main segments includes: (1) validation of RS-based IR and MW-retrieved Land Surface Temperature (LST) products, (2) studying snow wetness by developing, validating, and calibrating a Snow Wetness Profiler, (3) development of a regression tree algorithm capable of estimating snow depth based on radiative (MW observations) and physical snowpack properties, and (4) development of a global MW-RS-based snow depth product built on the regression tree algorithm.

A predictive model based on Regression Tree (RT) is developed in order to model snow depth and water equivalent at the Cooperative Remote Sensing Science and Technology Center – Snow Analysis and Field Experiment (CREST-SAFE). The RT performance analyzed based on contrasting training error, true prediction error, and variable importance estimates. The RT algorithm is then taken to a broader scale, and Japan Aerospace Exploration Agency (JAXA) Global Change Observation Mission – Water 1 (GCOM-W1) MW brightness temperature measurements were used to provide snow depth and SWE estimates. These SD and SWE estimates were evaluated against twelve (12) Snow Telemetry (SNOTEL) sites owned by the National Resources Conservation Service (NRCS) and JAXA’s own snow depth product. Results demonstrated that a RS MW-based RT algorithm is capable of providing snow depth and SWE estimates with acceptable accuracy for the continental United States, with some limitations. The major setback to the RT algorithm is that it will only provide estimates based on the data with which it was trained. Therefore, it is recommended that the work be expanded, and data from additional in-situ stations be used to re-train the RT algorithm. The CREST snow depth and water equivalent product, as it was named, is currently operational and publicly accessible at https://www.noaacrest.org//snow/products/.

The Cienega de Santa Clara is a 5600 ha, anthropogenic wetland in the delta of the Colorado River in Mexico. It is the inadvertent creation of the disposal of brackish agricultural waste water from the U.S. into the intertidal zone of the river delta in Mexico, but has become an internationally important wetland for resident and migratory water birds. The marsh is dominated by Typha domengensis with Phragmites australis as a sub-dominant species in shallower marsh areas. The most important factor controlling vegetation density was fire. The second significant (P<0.01) factor controlling NDVI was flow rate of agricultural drain water from the U.S. into the marsh. Reduced summer flows in 2001 due to canal repairs, and in 2010 during the YDP test run, produced the two lowest NDVI values of the time series from 2000 to 2011 (P<0.05). Salinity is a further determinant of vegetation dynamics as determined by greenhouse experiments, but was nearly constant over the period 2000 to 2011, so it was not a significant variable in regression analyses. Evapotranspiration (ET) and other water balance components were measured in Cienega de Santa Clara; we used a remote sensing algorithm to estimate ET from meteorological data and Enhanced Vegetation Index values from the Moderate Resolution Imaging Spectrometer (MODIS) sensors on the Terra satellite. We used Landsat NDVI imagery from 1978-2011 to determine the area and intensity of vegetation and to estimate evapotranspiration (ET) to construct a water balance. Remote sensing data was supplemented with hydrological data, site surveys and literature citations. The vegetated area increased from 1978 to 1995 and has been constant at about 4200 ha since then. The dominant vegetation type is Typha domingensis (southern cattail), and peak summer NDVI since 1995 has been stable at 0.379 (SD = 0.016), about half of NDVI(max). About 30% of the inflow water is consumed in ET, with the remainder exiting the Cienega as outflow water, mainly during winter months when T. domingensis is dormant.

Increasing atmospheric levels of carbon dioxide (CO2) and the potential impact on climate change has caused an increased effort to more accurately quantify terrestrial sources and sinks. Semiarid grasslands cover a significant portion of the Earth's land surface and may be an important sink for atmospheric CO2. This study was conducted to examine the role semiarid grasslands play in the carbon cycle. The relation between surface reflectance and temperature obtained from satellite imagery was used to determine a Water Deficit Index (WDI) to estimate distributed plant transpiration rates for a point in time. Due to the relationship between transpiration and plant CO2 uptake, WDI was directly related to CO2 flux. Satellite images were acquired for a five-year period (1996-2000) during which transpiration and net CO2 flux were measured for a semiarid grassland site in southeastern Arizona. Manual and automatic chamber data were also collected in 2005 and 2006 and used to assess the spatial variability of nighttime soil respiration. Spatial analysis showed the most influential factor affecting nighttime respiration was aspect, where flux from North-facing slopes was significantly (P < 0.05) higher than on South-facing slopes. A strong linear relationship (R2 = 0.97) existed between WDI-derived instantaneous net CO2 flux and daytime net CO2 flux estimates, and was used to generate maps of distributed daytime net CO2 flux. A linear relationship (R2 = 0.88) was also found between daytime and nighttime net CO2 flux, and used in combination with maps of daytime net CO2 flux to create maps of daily net CO2 flux. This study indicated that remote sensing offers an operational, physically-based means of obtaining daily net CO2 flux in semiarid grasslands.

Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Dr. Paul G. Steffes; Committee Member: Dr. Gregory D. Durgin; Committee Member: Dr. Robert D. Braun; Committee Member: Dr. Thomas K. Gaylord; Committee Member: Dr. Waymond R. Scott

A remote sensing survey was conceived to assess the relevance and appropriateness of a low-costing imaging spectrometry system, CASI (Compact Airborne Spectrographic Imager) applied as an airborne tool for coastal water assessment of Loch Linnhe (Scotland, UK). The system is described and compared in detail with other conventional and operational remote sensing instruments based on published reports and general scientific literature. It became clear in the case of Loch Linnhe that an airborne platform is the only viable possibility for monitoring by remote sensing, due to both the low likelihood of cloud-free satellite data and the relatively small size of such a fiord system. A survey plan is proposed which accommodates the environmental, logistical and technological constraints deemed likely to emerge during the data acquisition period. This work encompassed the use of other ancillary instruments, namely two portable spectroradiometers (SPECTRON SE-590) and an airborne multispectral scanner (DAEDALUS 1268) to enable both the comparison and calibration in support of the main data source. The availability of sea-truth (collected for one week each month over a period of two months during 1991) was entirely the responsibility of the Scottish Office Agriculture and Fisheries Department (SOAFD) who generously made the data available to this project. Although this in situ data could not be gathered absolutely in concurrence with the survey flights, their careful use proved essential to the project. A methodology based on the tidal behaviour within the sea-loch is proposed, from which sea-truth is derived.

The diversity of habitats in water bodies like rivers is characterised by the status of morphological and hydrological conditions. The good ecological status of water bodies is claimed in the EuropeanWater Framework Directive. For the assessment of this status the hydro-morphology is one of the most important supporting components for the classification of the ecological status of water bodies. Therefore the periodical monitoring is a mandatory measure in the scope of the European Water Framework Directive. Regarding the so called overview-method of the LAWA (German Working Group on water issues of the Federal States and the Federal Government represented by the Federal Environment Ministry) the use of remote sensing data and remote sensing methodologies becomes more important. Therefore remote sensing data on different scales (satellite, aerial photographs) as well as other topographic information (ATKIS) and a high resolution DTM are merged into an integrative process of analysis using remote sensing and GIS methodology. The analyses ared focused on two parameters. First, a detailed landuse classification based on LANDSAT satellite data is performed for whole catchment of a small river. The results show significant increase of urban areas close to the river. The second analyses deals with the determination of river curvature and introduces the use of a quasi-continously representation of the river. An additional challenge is the chosen study area of a low mountain range river. While large rivers are clear visible in remote sensing data, the usability and transformation of the well-established algorithms and work ows to small rivers need a further substantial research.

The preponderance of evidence shows that the warming of the climate system affects natural systems, leading to accelerations in the global hydrological cycle. This thesis discusses hydrological processes and introduces a new multivariate framework to improve drought characterisation/regionalisation in West Africa. Protocols that supports the practical assessment of the influence of global climate and reservoir systems on West Africa’s terrestrial hydrology are outlined. Complementary perspectives on hydrological controls on surface vegetation dynamics are also highlighted.

Ultra-spectrometers with a spectral resolution better than 1 cm_-1, such as AIRS on the AQUA, IASI on the Metop-A/B, and CrIS on the Suomi-NPP, have become operational during the past decade. The radiance spectra measured by these satellite-borne spectrometers provide soundings of the atmosphere with relatively high vertical resolution and high accuracy except for the lower atmosphere. Meanwhile, many ground-based ultra-spectrometers based on the Michelson Interferometer have been incorporated into the Department of Energy Atmospheric Radiation Measurement facilities and aboard NOAA research vessels. These instruments provide temperature and water vapor soundings within the planetary boundary layer continuously with very high vertical resolution. This dissertation develops a retrieval procedure which can combine the radiance measured by ground-based spectrometers and coincident observation from satellite-borne instruments to improve retrieval results throughout the lower atmosphere.

To verify the feasibility and improved accuracy of the combined retrieval, 90 clear sky cases from four in-situ radiosonde measurement locations or geographical regions, were selected for this study. Each region consists of radiosonde measurements of temperature and water vapor, downwelling radiance spectra measured at approximately the balloon launch time, and upwelling radiance observation by IASI at the location and time coincident with the surface radiance and radiosonde measurements.

These cases indicate, that when compared with the retrieval from upwelling radiance or downwelling radiance spectra only, there is a significant improvement of the retrieval using combined upwelling and downwelling radiance spectra is observed. At altitude below the 800 hPa pressure level, the errors using the combined retrieval are about 0.5 – 1 K in temperature, and 20 – 40 % for water vapor mixing ratio. These errors are approximately one-third the magnitude of errors for the sounding retrieval obtained using satellite upwelling radiance alone.

This research has involved the conduct of a series of laboratory measurements of the centimeter-wavelength opacity of water vapor along with the development of a hybrid radiative transfer ray-tracing simulator for the atmosphere of Jupiter which employs a model for water vapor opacity derived from the measurements. For this study an existing Georgia Tech high-sensitivity microwave measurement system (Hanley and Steffes , 2007) has been adapted for pressures ranging from 12-100 bars, and a corresponding temperature range of 293-525°K. Water vapor is measured in a mixture of hydrogen and helium. Using these measurements which covered a wavelength range of 6--20 cm, a new model is developed for water vapor absorption under Jovian conditions. In conjunction with our laboratory measurements, and the development of a new model for water vapor absorption, we conduct sensitivity studies of water vapor microwave emission in the Jovian atmosphere using a hybrid radiative transfer ray-tracing simulator. The approach has been used previously for Saturn (Hoffman, 2001), and Venus (Jenkins et al., 2001). This model has been adapted to include the antenna patterns typical of the NASA Juno Mission microwave radiometer (NASA/Juno -MWR) along with Jupiter's geometric parameters (oblateness), and atmospheric conditions. Using this adapted model we perform rigorous sensitivity tests for water vapor in the Jovian atmosphere. This work will directly improve our understanding of microwave absorption by atmospheric water vapor at Jupiter, and improve retrievals from the Juno microwave radiometer. Indirectly, this work will help to refine models for the formation of Jupiter and the entire solar system through an improved understanding of the planet-wide abundance of water vapor which will result from the successful opreation of the Juno Microwave Radiometer (Juno-MWR).

The ability to map industrial discharges through remote sensing provides a powerful tool in environmental monitoring. Radionuclide effluents have been discharged, under authorization, into the Irish Sea from BNFL (British Nuclear Fuels Plc.) sites at Sellafield and Springfields since 1952. The quantitative mapping of this anthropogenic radioactivity in estuarine intertidal zones is crucial for absolute interpretations of radionuclide transport. The spatial resolutions of traditional approaches e.g. point sampling and airborne gamma surveys are insufficient to support geomorphic interpretations of the fate of radionuclides in estuaries. The research presented in this thesis develops the use of airborne remote sensing to derive high-resolution synoptic data on the distribution of anthropogenic radionuclides in the intertidal areas of the Ribble Estuary, Lancashire, UK. From multidate surface sediment samples a significant relationship was identified between the Sellafieldderived 137Cs & 241Am and clay content (r2=0.93 & 0.84 respectively). Detailed in situ, and laboratory, reflectance (0.4-2.5mn) experiments demonstrated that significant relationships exist between Airborne Thematic Mapper (ATM) simulated reflectance and intertidal sediment grain-size. The spectral influence of moisture on the reflectance characteristics of the intertidal area is also evident. This had substantial implications for the timing of airborne image acquisition. Low-tide Daedalus ATM imagery (Natural Environmental Research Council) was collected of the Ribble Estuary on May 30th 1997. Preprocessing and linear unmixing of the imagery allowed accurate sub-pixel determinations of sediment clay content distributions (r2=0.8 1). Subsequently, the established relationships between 137Cs & 241Am and sediment grain-size enabled the radionuclide activity distributions across the entire intertidal area (92km2) to be mapped at a geomorphic scale (1.75m). The accuracy of these maps was assessed by comparison with in situ samples and the results of previous radiological studies within the estuary. Finally, detailed conclusions are made regarding radionuclide sinks and sources, and surface activity redistribution within the Ribble Estuary environment.

Semi-analytical models for remote sensing of water quality parameters need to be parameterized with specific inherent optical properties. In this thesis, data on specific inherent optical properties of Swedish lakes and coastal waters is presented. Also, the problems of measuring in situ spectral backscattering are addressed. It is shown how measured specific inherent optical properties are used to parameterize semi-analytical bio-optical models. The models are then used to produce large synthetic data sets based on the distribution of water quality parameters, and from these data sets, band ratio or single band ratio algorithms for remote estimation of water quality parameters are constructed. A similar model was also used to calculate under water PAR from measured water quality parameters.

The specific inherent optical properties of Swedish lakes and coastal waters are very similar to earlier reported data from the oceanic environment. However, different relations of the water quality parameters will affect the inherent optical properties absorption and backscattering. The absorption spectra are dominated by yellow substance with terrestrial origin. Phytoplankton absorption is low, and account in general only for about 10 % of the total absorption in regions where phytoplankton pigments are active. The spectral backscattering is dominated by suspended particulate inorganic matter. Phytoplankton backscattering is almost negligible, except in cases where the phytoplankton community is dominated by highly scattering cyanobacteria. Experiences from remote sensing campaigns and modeling shows that remote chlorophyll estimation is most effective at longer wavelengths, where the absorption of yellow substance is low. However, modeling also predicts that large uncertainties have to be expected in the estimation of chlorophyll, both from variation in the specific phytoplankton absorption and from influences of other optically active water quality parameters.

Accurate estimates of soil moisture are necessary to predict evapotranspiration, runoff, infiltration, and groundwater recharge and, through these variables, weather, climate, and fire and flood frequencies. This dissertation is motivated by the need to estimate soil water content from remotely sensed passive microwave emission. Two different approaches are taken: (1) improved modeling of the microwave emission from the land surface; and (2) measurements of the average dielectric properties of the soil media and vegetation canopies. Consequently, the first part of the dissertation describes how a stratified dielectric model of the microwave emission from the soil was extended to take into account the effects of vegetation. The model parameters were calibrated using observed data and a robust optimization routine. However, the availability of measurements of some of these parameters, particularly the profile of dielectric permittivity of the canopy, would facilitate a more complete evaluation of the accuracy of the extended microwave emission model. The second part of this dissertation describes progress towards the development of a technique to measure the dielectric of vegetation canopies. This technique is based on gated time domain transmission measurements through the substance of interest. Preliminary studies carried out using soils with varying salinity and water content and vegetation show (1) an unexpected response of the signal to saline soils, and (2) a possible dielectric signature of the onset of stress in plant stems.

This dissertation investigated the estimation of global cloud water amounts. The study was prompted by the large discrepancy in published global mean values of cloud liquid water path. Microwave and optical satellite measurements of this quantity range from 25 g/m² to 80 g/m². Theoretical estimates are significantly larger with a current best guess value of 380 g/m². The major limitations of microwave measurements were found to be the inadequate separation of the cloud- and rainwater components, and the lack of retrievals over land. Optical observations were found to be constrained by the truncation of retrieved optical thickness due to saturation effects, the limited knowledge of drop effective radius as a function of optical thickness and rain rate, and plane-parallel retrieval errors due to 3D effects. An analysis of the potential uncertainties concluded that the current theoretical estimate of the global mean cloud liquid water path of 380 g/m² was reasonable with an uncertainty of ±80 g/m². Errors in the optical retrievals due to 3D effects were estimated using a multiangle data set. A microwave-optical comparison revealed that a drop effective radius significantly larger than the common assumption of 8-10 μm was required to remove the low bias of optical retrievals of cloud liquid water in precipitating systems. The low bias due to saturation effects was accounted for by sigmoidal extrapolation of the cumulative distribution of cloud optical thickness. Overall it was found that the optical measurement of the global mean cloud liquid water path could be increased to a maximum of 150 g/m² over the oceans. The failure to close the gap between satellite measurements and theoretical estimates can partly be attributed to, but cannot be completely explained by, the lack of the most intense continental clouds in the ocean-only data set used in this study. It is unlikely that optical measurements can be corrected to accurately retrieve the largest liquid water amounts. New techniques are required to handle the wettest precipitating clouds.

L'estimació dels recursos hídrics de les superfícies continentals a escala regional i global és fonamental per a una bona gestió dels recursos hídrics. Aquesta estimació cobreix una àmplia gamma de temes i camps, incloent-hi la caracterització dels sòls i dels recursos hídrics a l’escala de la conca, la modelització hidrològica i la predicció i la cartografia d'inundacions. En aquest context, la caracterització dels estats de la superfície continental, per a obtenir millors paràmetres d’entrada als models hidrològics, és essencial per millorar la precisió en la simulació de cabals, sequeres i inundacions. L’estimació del contingut d’aigua en el sistema, incloses les diferents masses d’aigua i l’aigua lliure en el sòl, és especialment necessària per a una descripció precisa dels processos hidrològics i, en general, del cicle de l’aigua a les superfícies continentals. Per caracteritzar millor els processos hidrològics, les intervencions antropogèniques no es poden negligir. L'home influeix en el cicle de l'aigua, principalment mitjançant el reg i la construcció de preses, fet que s’ha de quantificar correctament. L’objectiu de la tesi és la millora de l’estimació remota dels recursos hídrics, incloent-hi la quantificació dels factors antròpics, mitjançant l’ús de diversos sensors llançats recentment, aprofitant recents desenvolupaments en la tecnologia de teledetecció. Amb l'arribada de les constel·lacions Sentinel (Sentinel-1, 2, 3), disposem de millors eines per estimar els recursos hídrics, incloent-hi els impactes humans, amb una major precisió i cobertura. Aquest treball de tesi consta principalment de dues línies de recerca on s’estimen les intervencions humanes en el cicle hidrològic: la cartografia del reg (com a aplicació en humitat del sòl), i el forçament d’embassaments en simulacions hidrològiques (com a aplicació de l’altimetria). En la primera linia s’estima la humitat del sòl a partir de l’anàlisi estadística de les dades SAR de Sentinel-1. Es desenvolupen dues metodologies per obtenir la humitat del sòl amb una resolució espacial de 100 m basant-se en la interpretació de les dades de Sentinel-1 obtingudes amb la polarització VV (vertical-vertical), que es combina amb dades òptiques Sentinel-2 per a l'anàlisi dels efectes de la vegetació. Com aplicació de la humitat del sòl, es cartografia el reg en diverses condicions meteorològiques, i amb una alta resolució espacial i temporal. Es proposa una metodologia per a la cartografia del reg mitjançant dades SAR obtingudes en polaritzacions VV (vertical-vertical) i VH (vertical-horitzontal). A partir de la sèrie temporal Sentinel-1, s’analitzen diferents estadístiques i mètriques, incloent-hi el valor mitjà, la variància del senyal, la longitud de la correlació i la dimensió fractal, a partir dels quals es classifiquen els arbres irrigats, els cultius irrigats i els cultius no irrigats. En la segona línia, s’estima el nivell dels embassaments a partir de les dades d’altimetria de Sentinel-3, amb l’altímetre SAR (SRAL), basant-se en diferents algorismes per millorar la precisió. Aquest estudi presenta tres algorismes especialitzats o retrackers destinats a obtenir el nivell de la superfície dels cossos d’aigua estudiats, minimitzant la contaminació de les formes d’ona degut al sòl que els envolta. Es compara el rendiment del mètode proposat de selecció de la porció d’ona amb tres retrackers, és a dir, un retracker de llindar, el retracker del centre de gravetat (OCOG) i un retracker de base física de dos passos. S’obtenen sèries temporals del nivell de la làmina d’aigua d’embassaments situats a la conca del riu Ebre (Espanya). Com aplicació, les sèries de nivell dels embassaments obtingudes s’utilitzen per a forçar els embassaments en simulacions hidrològiques.
La estimación de los recursos hídricos de las superficies continentales a escala regional y global es fundamental para una buena gestión de los recursos hídricos. Esta estimación cubre una amplia gama de temas y campos, incluyendo la caracterización de los suelos y de los recursos hídricos a escala de cuenca, la modelización hidrológica y la predicción y la cartografía de inundaciones. En este contexto, la caracterización de los estados de la superficie continental, para obtener mejores parámetros de entrada para los modelos hidrológicos, es esencial para mejorar la precisión en la simulación de caudales, sequías e inundaciones. La estimación del contenido de agua en el sistema, incluidas las diferentes masas de agua y el agua libre en el suelo, es especialmente necesaria para una descripción precisa de los procesos hidrológicos y, en general, del ciclo del agua en las superficies continentales. Una caracterización precisa de los procesos hidrológicos requiere no descuidar las intervenciones humanas. El hombre influye en el ciclo del agua, principalmente mediante el riego y la construcción de embalses, lo que se debe cuantificar correctamente. El objetivo de la tesis es la mejora de la estimación remota de los recursos hídricos, incluyendo la cuantificación de los factores humanos, mediante el uso de varios sensores lanzados recientemente, aprovechando recientes desarrollos en la tecnología de teledetección. Con la llegada de las constelaciones Sentinel (Sentinel-1, 2, 3), disponemos de mejores herramientas para estimar los recursos hídricos, incluyendo los impactos humanos, con una mayor precisión y cobertura. Este trabajo de tesis consta principalmente en dos ejes de investigación donde se estiman las intervenciones humanas en el ciclo hidrológico: la cartografía del riego (como aplicación en humedad del suelo), y el forzamiento de embalses en simulaciones hidrológicas (como aplicación de la altimetría). En relación al primer eje, se estima la humedad del suelo a partir del análisis estadístico de los datos SAR de Sentinel-1. Se desarrollan dos metodologías para obtener la humedad del suelo con una resolución espacial de 100 m basándose en la interpretación de los datos de Sentinel-1 obtenidas con la polarización VV (vertical-vertical), que se combina con datos ópticas Sentinel-2 para el análisis de los efectos de la vegetación. Como aplicación de la humedad del suelo, se cartografía el riego en diversas condiciones meteorológicas, y con una alta resolución espacial y temporal. Se propone una metodología para la cartografía del riego mediante datos SAR obtenidos en polarizaciones VV (vertical-vertical) y VH (vertical-horizontal). A partir de la serie temporal Sentinel-1, se analizan diferentes estadísticas y métricas, incluyendo el valor medio, la varianza de la señal, la longitud de la correlación y la dimensión fractal, a partir de los cuales se clasifican los árboles irrigados, los cultivos irrigados y los cultivos no irrigados. En el segundo eje, se estima el nivel de los embalses a partir de los datos de altimetría de Sentinel-3, con el altímetro SAR (SRAL), basándose en diferentes algoritmos para mejorar la precisión. Este estudio presenta tres algoritmos especializados o retrackers destinados a obtener el nivel de la superficie de los cuerpos de agua estudiados, minimizando la contaminación de las formas de onda debido al suelo que los rodea. Se compara el rendimiento del método propuesto de selección de la porción de onda con tres retrackers, es decir, un retracker de umbral, el retracker del centro de gravedad (OCOG) y un retracker de base física de dos pasos. Se obtienen series temporales del nivel de la lámina de agua de embalses situados en la cuenca del río Ebro (España). Como aplicación, las series de nivel de los embalses obtenidas se utilizan para forzar los embalses en simulaciones hidrológicas.
The estimation of the water resources of the continental surfaces at a regional and global scale is fundamental for good water resources management. This estimation covers a wide range of topics and fields, including the characterisation of soils and water resources at the basin scale, hydrological modelling and flood prediction and mapping. In this context, the characterisation of the states of the continental surface, to obtain better input parameters for hydrological models, is essential to improve the precision in the simulation of flows, droughts, and floods. The estimation of the water content in the system, including the different water bodies and the free water in the soil, is especially necessary for a precise description of the hydrological processes and, in general, of the water cycle on the continental surfaces. To better characterise hydrological processes, human interventions cannot be neglected. Humans influence the water cycle, mainly through irrigation and the construction of reservoirs, which must be correctly quantified. The objective of the thesis is the improvement of the remote estimation of water resources, including the quantification of human factors, using several sensors recently launched, taking advantage of recent developments in remote sensing technology. With the arrival of the Sentinel constellations (Sentinel-1, 2, 3), we have better tools to estimate water resources, including human impacts, with greater precision and coverage. This thesis consists mainly of two parts where human interventions in the water cycle are considered: irrigation cartography (as an application of soil moisture), and the forcing of reservoirs in hydrological simulations (as an application of altimetry). Firstly, soil moisture is estimated from the statistical analysis of Sentinel-1 SAR data. Two methodologies are developed to obtain soil moisture with a spatial resolution of 100 m based on the interpretation of Sentinel-1 data collected with the VV polarization (vertical-vertical), which is combined with optical data of Sentinel-2 for the analysis of the effects of vegetation. Secondly, irrigation is mapped under various meteorological conditions, including high spatial and temporal resolution. A methodology for irrigation mapping is proposed using SAR data obtained in VV (vertical-vertical) and VH (vertical-horizontal) polarizations. With Sentinel-1 time series, different statistics and metrics are analysed, including the mean value, the variance of the signal, the correlation length and the fractal dimension, based on which the classification of irrigated trees, irrigated crops, and non-irrigated crops are derived. Finally, the level of the reservoirs is estimated from the Sentinel-3 altimetry data, with the SAR altimeter (SRAL), based on different algorithms to improve the accuracy. This study presents three specialised algorithms or retrackers designed to obtain the level of the surface of the studied inland bodies of water, minimising the contamination of the waveforms due to the surrounding soil. The performance of the selection method of the proposed wave portion is compared with three retrackers, that is, the centre of gravity retracker (OCOG) and the two-step physical-based retracker. Temporal series of the water level of reservoirs located in the basin of the Ebro River (Spain) are obtained. As an application, the level series of the reservoirs obtained are used to force the reservoirs in hydrological simulations.
L'estimation et le suivi des ressources en eau des surfaces continentales aux niveaux régional et global est essentielle pour la gestion du bilan hydrique, particulièrement dans le contexte des changements climatiques et anthropiques. Ils couvrent un large éventail de thèmes et de domaines, incluant la caractérisation des ressources en eau à l'échelle du bassin, la modélisation hydrologique ainsi que la prévision et la cartographie des inondations. Dans ce contexte, la caractérisation des états de surface, en tant que paramètres d’entrée dans les modèles hydrologiques, est essentielle pour obtenir une meilleure précision de la simulation, qui est liée à la précision prévisionnelle des débits des cours d’eau et le suivi des sécheresses et des inondations. L'estimation de la teneur en eau des surfaces continentales, incluant l’état hydrique du sol et les niveaux des surfaces couvertes d’eau, est particulièrement nécessaire pour une description précise des processus hydrologiques et plus généralement du cycle de l'eau sur les surfaces continentales. Afin de mieux comprendre les processus hydrologiques, l'influence humaine (l’effet anthropique) sur le cycle de l'eau nécessite une évaluation fine. Elle est particulièrement liée à la gestion de l’irrigation et la construction de barrages. L'objectif de la thèse était d'améliorer l'estimation des ressources en eau et une meilleure caractérisation des interventions anthropiques à travers l'utilisation de nouveaux capteurs satellitaires multi-configurations du programme européen Copernicus. Avec le développement de la technologie de télédétection spatiale, et plus particulièrement avec l’arrivée des constellations Sentinel (Sentinel-1, 2, 3) à haute résolution spatiale et temporelle, il existe un meilleur outil pour estimer les états des surfaces continentales. Ce travail de thèse comprend principalement deux priorités liées à des interventions humaines dans le cycle hydrologique:la cartographie de l'irrigation en tant que action humaine liée directement à l'humidité du sol et le forçage des barrages dans un modèle de simulation de rivière en tant qu'application liée à l’estimation du niveau de l'eau libre. Un premier axe de recherche a été basé sur une analyse statistique des données SAR Sentinel-1 pour caractériser l’état hydrique du sol. Deux méthodes ont été développées pour estimer ce paramètre avec une résolution spatiale de 100 m. Elles sont basées sur des approches de détection de changement à partir des données Sentinel-1 acquises en polarisation VV (verticale-verticale), combinées aux données optiques Sentinel-2 pour corriger les effets de la végétation. L’application consistait à cartographier l'irrigation, avec des résolutions spatiale et temporelle élevées. Une méthodologie de cartographie de l'irrigation utilisant des données SAR Sentinel-1 a été proposée. Elle estbasée sur les acquisitions en polarisations VV (vertical-vertical) et VH (vertical-horizontal). A partir de la série temporelle des mesures Sentinel-1, des paramètres statistiques tel que la valeur moyenne, la variance du signal, la longueur de corrélation temporelle et la dimension fractale, sont analysées, en fonction du type de culture; cultures annuelles irriguées, arbres irrigués et cultures pluviales. Des classifications supervisées utilisant les approches Random Forest et SVM sont testées. En deuxième axe, l'estimation de la hauteur de la surface de l'eau à partir des données altimétriques de Sentinel-3 avec l’altimètre SAR (SRAL) a été réalisée à l'aide de différents algorithmes afin d'améliorer la précision sur des petites surfaces. Cette étude présente trois algorithmes spécialisés (ou retrackers) dédiées à la minimisation de la contamination des sols par les formes d’ondes permettant de récupérer les niveaux d’eau à partir de données altimétriques SAR sur des masses d’eaux intérieures. Les performances de la méthode de sélection de portion de forme d'onde proposée avec trois retrackers, à savoir, le retracker à seuil, le retracker à centre de gravité décalé (OCOG) et le retracker à base physique à 2 étapes, sont comparées. Des séries chronologiques de niveaux d'eau sont extraites pour les masses d'eau du bassin de l'Èbre (Espagne). Une application des produits altimétriques est proposée. Le produit de niveau d’eau a été utilisé comme paramètre d’entrée pour analyser l’effet tampon des barrages dans les simulations de débits fluviaux.