Academic literature on the topic 'Non-contact aerial survey'

Conducting topographic surveys in active mines is challenging due ongoing operations and hazards, particularly in highwalls subject to constant and active mass movements (rock and earth falls, slides and flows). These vertical and long surfaces are the core of most mines, as the mineral feeding mining production originates there. They often lack easy and safe access paths. This framework highlights the importance of accomplishing non-contact high-accuracy and detailed topographies to detect instabilities prior to their occurrence. We have conducted drone flights in search of the best settings in terms of altitude mode and camera angle, to produce digital representation of topographies using Structure from Motion. Identification of discontinuities was evaluated, as they are a reliable indicator of potential failure areas. Natural shapes were used as control/check points and were surveyed using a robotic total station with a coaxial camera. The study was conducted in an active kaolin mine near the Alto Tajo Natural Park of East-Central Spain. Here the 140 m highwall is formed by layers of limestone, marls and sands. We demonstrate that for this vertical landscape, a facade drone flight mode combined with a nadir camera angle, and automatically programmed with a computer-based mission planning software, provides the most accurate and detailed topographies, in the shortest time and with increased flight safety. Contrary to previous reports, adding oblique images does not improve accuracy for this configuration. Moreover, neither extra sets of images nor an expert pilot are required. These topographies allowed the detection of 93.5% more discontinuities than the Above Mean Sea Level surveys, the common approach used in mining areas. Our findings improve the present SfM-UAV survey workflows in long highwalls. The versatile topographies are useful for the management and stabilization of highwalls during phases of operation, as well closure-reclamation.

Geostructural rock mass surveys and the collection of data related to discontinues provide the basis for the characterization of rock masses and the study of their stability conditions. This paper describes a multiscale approach that was carried out using both non-contact techniques and traditional support techniques to survey certain geometrical features of discontinuities, such as their orientation, spacing, and useful persistence. This information is useful in identifying the possible kinematics and stability conditions. These techniques are extremely useful in the case study of the Elva valley road (Northern Italy), in which instability phenomena are spread across 9 km in an overhanging rocky mass. A multiscale approach was applied, obtaining digital surface models (DSMs) at three different scales: large-scale DSM of the entire road, a medium-scale DSM to assess portions of the slope, and a small-scale DSM to assess single discontinuities. The georeferenced point cloud and consequent DSMs of the slopes were obtained using an unmanned aerial vehicle (UAV) and terrestrial photogrammetric technique, allowing topographic and rapid traditional geostructural surveys. This technique allowed us to take measurements along the entire road, obtaining geometrical data for the discontinuities that are statistically representative of the rock mass and useful in defining the possible kinematic mechanisms and volumes of potentially detachable blocks. The main purpose of this study was to analyse how the geostructural features of a rock mass can affect the stability slope conditions at different scales in order to identify road sectors susceptible to different potential failure mechanisms using only kinematic analysis.

Large whales, including the endangered sei whale (Balaenoptera borealis), sperm whale (Physeter macrocephalus), and North Atlantic right whale (Eubalaena glacialis), are known to occur in the New York Bight. However, relatively little data exist on social behavior typical of these species in the area. The U.S. Mid-Atlantic has traditionally been considered a large whale migratory corridor with few surveys documenting social dynamics of whale presence in these waters. To better understand the occurrence, distribution, abundance, and behavior of these species for management and conservation planning, monthly line-transect aerial surveys were conducted over a 3-year period from March 2017 to February 2020. During these surveys, three noteworthy socio-sexual behavior events were observed and photographed within groups of sei whales (April 2019), sperm whales (September 2019), and right whales (December 2019). Events included what could be either non-reproductive sexual behavior (socio-sexual behavior) or sexual behavior (copulation) among conspecifics, including mirror pair swimming, lateral and vertical presenting, and belly to belly contact. During all three events, groups were highly active at the surface, frequently and quickly changing speed and direction, and animals were predominantly less than one body length apart from other conspecifics in the group. All species were recorded rolling onto their sides and/or back while at or near the surface. Open mouth display occurred in the North Atlantic right whale event. Though copulation is unlikely to have transpired during the sperm whale event and could not have occurred during the right whale event due to the identification of same-sex individuals, it cannot be ruled out as the impetus for the sei whale event. These observations begin to describe the relative importance of the New York Bight as more than a migratory corridor and suggest that additional behaviorally focused data collection be incorporated into future surveys.

Protecting the living environment has become one of the greatest human concerns; sudden increase of population, industry and technology development, unrestrained over consumption of the citizens and climate changes, have all caused many problems for mankind. Shores are special zones that are in contact with three Atmosphere, Hydrosphere and Lithosphere environments of earth. Shore lines are of the most important linear features of the earth’s surface which have an animated and alive nature. In this regard, optimized management of the shores and environmental protection for stable development require observing the shorelines and their variations. Protection of shorelines within appropriate time periods is of high importance for the purpose of optimized management of the shores. The twenty first century has been called the era of information explosion. A time that, through benefits of new technologies, information experts attempt to generate more and up to date information in various fields and to provide them for managers and decision makers in order to be considered for future planning and also to assist the planners to arrange and set a comprehensive plan. <br><br> Aerial images and remote sensing technology are economic methods to acquire the required data. Such methods are free from common time and place limitations in survey based methods. Among remote sensing data, the ones acquired from optical images have several benefits which include low cost, interpretation simplicity and ease of access. That is why most of the researches concerning extraction of shorelines are practiced using optical images. On the other hand, wide range coverage of satellite images along with rapid access to them caused these images to be used extensively for extracting the shorelines. <br><br> The attempt in this research is to use satellite images and their application in order to study variations of the shorelines. Thus, for this purpose, Landsat satellite images from TM and ETM+ sensors in the 35 time period has been used. In order to reach better results, images from MODIS satellite has been used as auxiliary data for the images that are with an error margin. Initial classification on the images was conducted to distinguish water and non water applications. Neural network classification was applied with specific scales on the images and the two major applications were thereby extracted. Then, in order to authenticate the proceedings, Error matrix and Kappa coefficient has been applied on the classified images. Base pixel method of neural network was used for the purpose of information extraction while authenticity of that was evaluated too. The outcomes display the trend of Urmia shoreline has been approximately constant between the years of 1976 to 1995 and has experienced very low variations. In 1998 the lake experienced increase of water and therefore advancement of the shoreline of the lake due to increase of precipitation and the volume of inflowing water to the basin. During 2000 to 20125, however, the lake’s shoreline has experienced a downward trend, which was intensified in 2007 and reached to its most critical level ever since, that is decreasing to about one third. <br><br> Further, temporal and spatial potentiality evaluation of clouds seeding in Urmia lake zone has been studied as a solution for improvement and recovery of the current status of the lake, and an algorithm was proposed for optimized temporal- spatial study on could seeding. Ecological, meteorological and synoptic data were used for timing study of the cloud’s seeding plan, which upon study; it is easy to evaluate precipitation potential and quality of the system. At the next step, the rate of humidity and also stability of the precipitating system can be analyzed using radar acquired data. Whereas extracted date from MODIS images are expressing the spatial position, therefore in order to study the location of the cloud’s seeding, MODIS images of the selected time intervals along with applying MCM algorithm were used to conclude thick clouds. Also, with interpolation of the TRMM data, it is possible to deduce maximum precipitation in the form of spatial arena. One of the data categories that is used both for temporal and spatial analysis is radar images which in addition to time, displays the existing humidity range, movement direction, and positions of accumulated precipitation cores. Therefore, using this algorithm, it is possible to conclude the most optimized spatial position in order to execute the seeding plan.

Abstract The Saint-Gilles breccias, on the western flank of Piton des Neiges volcano, are clearly identified as debris avalanche deposits. A petrographic, textural and structural analysis of the breccias and inter-bedded autochthonous lava flows enables us to distinguish at least four successive flank slides. The oldest deposit sampled the hydrothermally-altered inner parts of the volcano, and has a large volume. Failure was favored by the presence of a deep intensely-weathered layer. The younger deposits are from superficial sources, as their products are rarely hydrothermalized and are more vesicular. The breccia formation, and especially the progressive breaking up occurring during the debris avalanche displacement, indicates the existence of high speed transport. In the Cap La Houssaye coastal area, abrasion and striation of the underlying lava formation, as well as the packing features observed in the breccia, are considered to be deceleration structures. Introduction Huge landslides of volcano flanks, whether or not initiated by magmatic intrusions, have been recognized as catastrophic events since the 1980 Mount St Helens eruption. On oceanic shield volcanoes, the contribution of failure to the edifice-building process was proposed by Moore [1964] and suggested elsewhere for Hawaii [Lipman et al., 1985 ; Moore et al., 1989], Reunion island [Lénat et al., 1989], Etna [McGuire et al., 1991], and Canarias [Carracedo, 1994, 1996 ; Marty et al., 1996]. This contribution is particularly obvious in island volcanoes showing a U-shaped caldera open to the ocean. Several mechanisms inherent to the causes of failure have been proposed, such as dyke intrusion [McGuire et al., 1990 ; Iverson, 1995 ; Voight and Elsworth, 1997], caldera collapse [Marty et al., 1997], or volcanic spreading [Borgia et al., 1992 ; van Wyk de Vries and Francis, 1997]. Invariably, other factors have been proposed as favorable to volcanic destabilization, such as the probable occurrence of deep low-cohesion layers due to the existence of pyroclastic or hyaloclastic layers [Duffield et al., 1982 ; Siebert, 1984] or an old basement. Gravity spreading models are now frequently proposed to explain the destruction of volcanic edifices [Borgia et al., 1992 ; Merle and Borgia, 1996 ; van Wyk de Vries and Borgia, 1996 ; van Wyk de Vries and Francis, 1997], most of them taking into account basal or intra-volcanic weakness zones. We propose that in such a scenario, density heterogeneity should be an important factor governing the slow evolution of the volcanic pile. Clague and Denlinger [1994] proposed a olivine-rich ductile basal layer that influences the stability of volcano flanks. On Reunion island, a large volcanic landslide has been proposed to explain the peculiar morphology of Piton de la Fournaise-Grand Brûlé [Vincent and Kieffer, 1978]. Bathymetric surveys [Bachèlery and Montagionni, 1983 ; Lénat et al., 1989, 1990 ; Cochonnat et al., 1990 ; Lénat and Labazuy, 1990 ; Labazuy, 1991 ; Bachèlery, 1995 ; Ollier et al., 1998] have confirmed the offshore occurrence of debris avalanche deposits. Similar deposits are also known to exist along the western, northern and southwestern submarine flanks of the Piton des Neiges volcano. Unlike other deposits showing inland prolongation, “Saint-Gilles breccias” displays a well-preserved and non-weathered texture and structure. Because of striking analogies between the “Saint-Gilles breccias” and, for example, the Cantal stratovolcano debris avalanche deposits [Cantagrel, 1995], we conclude that these formations are the products of repeated avalanches during the Piton des Neiges basaltic period [Bachèlery et al., 1996]. We propose an interpretation of their origin, emplacement mechanism and their role in the evolutionary process of the western flank of Piton des Neiges. Volcano-structural setting Mechanical instability of oceanic volcanic edifices generates huge flank landslides, with lateral and mainly submarine transport of sub-aerial materials. These landslides participate in the building of the lower submarine slopes of the volcano. Geophysical surveys have detected low cohesion materials in most offshore Reunion island areas [Malengrau et al., 1999 ; de Voogd et al., 1999 ; Lénat et al., 2001] showing that these materials have largely contributed to the construction of offshore Reunion Island. Such deposits are also found in the inner part (“Cirques”) of Piton des Neiges [Maillot, 1999]. On the other hand, electric and electromagnetic soundings have revealed a deep extending conductor within the Piton de la Fournaise volcanic pile [Courteaud et al., 1997 ; Lenat et al., 2000]. Interpretations about the nature and origin of this conductor depend on its location. In the central caldera zone, as revealed by SP positive anomalies [Malengrau et al., 1994 ; Zlotnicki et al., 1994], the hydrothermal and magmatic complex is probably responsible for the observed low resistivities. Along the flanks, such a hypothesis may not be realistic. Courteaud [1996] suggests the occurrence of a deep argilized layer of volcano-detritic origin. In any case, the hydrothermal complex with high fluid pressures and secondary minerals appears as a potential weak zone that may contribute to the volcano’s instability [Lopez and Williams, 1993 ; Frank, 1995]. Chronology and stratigraphy Extent of the debris avalanche deposits The various breccias found at the western end of Reunion island, on the Piton des Neiges volcano flank, cover a 16 km2 area between Cap Marianne and Saint-Gilles (fig. 1). They are overlain upwards (&gt; 250 to 300 m) by trachyandesitic (mugearite) lava flows of Piton des Neiges differentiated series [Billard, 1974]. Some restricted breccia outcrops in deep valleys from Bernica to the north up to l’Hermitage to the south indicate the existence of larger extension of the debris avalanche deposits. Furthermore, breccias with similar “Saint-Gilles” facies appear down the Maïdo cliff to Mafate “Cirque” at an altitude 1300 m, beneath 600 m of mugearite and some olivine basalt flows. Unpublished electromagnetic data (CSAMT soundings) confirm the inland continuity of the “Saint-Gilles breccias” up to the Maïdo along the Piton des Neiges western flank, hidden by mugearitic flows. Available bathymetric surveys offshore Saint Paul – Saint Gilles areas show the obvious underwater prolongation of “Saint-Gilles breccias” : a shallow depth (&lt; 100 m) plateau followed by a slope with hummocky surface down to 2 500 m depth [Bachèlery et al., 1996 and fig. 2]. From this data, the total surface of “Saint-Gilles” debris avalanche deposits is estimated as more than 500 km2. Chronology A coastal cliff, from Ravine Bernica to Boucan Canot, provides the best outcrop of the northern part of “Saint-Gilles breccias”, with a clear inter-bedding of breccia units and lava formations (photo 1and fig. 3). – The lower breccia unit (Br I), of unknown thickness, has a remarkable friable aspect and a grayish color. – The first autochthonous lava formation (L1) consists in thin pahoehoe olivine basalt flows filling large valleys dug into “Br I”. The top of this formation is striated by the overlying “Br II” unit (photo 2). – Breccia unit “Br II” is interbedded between L1 and L2 olivine basalts. More compact and massive, “Br II” is characterized by a reddish matrix and dark blocks, with many curved fracture surfaces. – On “Br II” or directly on L1, picritic basalt flows L2 are found, filling narrow valleys. – Breccia unit “Br III” lies on “Br II” with a striking sheared contact plane visible along the main road (photo 3). It is a typical debris avalanche deposit with large imbricate blocks within a fine-grained beige matrix. – Once again, basaltic flows of lava formation L3 fill a valley dug into “Br III” near Petite Anse river. – Breccia unit “Br IV” rests on L3 at Petite Anse, but its contact with “Br III” elsewhere is not clear. The facies of this unit is very similar to the “Br III”. All the breccia units are covered by basaltic and trachyandesitic flows from the end of the Piton des Neiges basaltic series, and differentiated series. In the Saint-Gilles river, two formations are superposed : picritic basalts (L4) have flowed on the “Br IV” breccia unit, latter aphyric trachy-andesitic (mugearite) flows (L6) overlapped L4 and the breccia landforms, reaching in places the coastal area. To the north, at Plateau Caillou, plagioclase-phyric basalt flows (L5) are found between mugearite and breccias. Elsewhere on Piton des Neiges, such flows are symptomatic of the transition from the basaltic series to the differentiated series [Billard, 1974]. The occurrence of autochthonous basaltic formations L1 to L3, inter-bedded with “Saint-Gilles breccias”, enables us to distinguish at least four superposed breccia units. Although the emplacement age of the lower “Br I” is not known precisely, it is overlain and therefore older than Cap Marianne pahoehoe lavas (L1) dated at 0.452 Ma [Mc Dougall, 1971]. On the other hand, the upper breccia units are younger than the pahoehoe olivine basalt at Cap la Houssaye dated at 0,435 Ma but older than L5 plagioclasic basalts dated at 0.35 Ma. Geological description of the “breccia sequence” In the synthetic lithologic log (fig. 4) of the Saint-Gilles area, autochthonous lava formations are clearly broken into four separate breccia units. Lava formations. – L1 formation consists of numerous thin pahoehoe olivine-rich to aphyric basaltic flows. Both L2 and L3 formations are characterized by a few thicker (decametric) olivine (frequently picritic) basalt flows. Breccia units. – All breccia units display common characteristics such as the universal association of two facies (photo 4) : (i) a matrix – sandy to silty – facies containing a non-sorted mixture of non-stratified heterogeneous materials ranging from granular size to blocky elements, (ii) coherent large blocks and large pieces (‘block’ facies) of various lithology such as lava flow, scorias, pyroclastics or other breccias ; blocks displaying frequent “jigsaw” features. The lower breccia unit “Br 1” (fig. 4) has a more compact but very heterogeneous aspect, with a chaotic distribution of blocks in a less-developed matrix. This unit is characterized by a deep hydrothermal alteration with a lot of zeolites, chlorite, clays, calcite and oxides. The upper breccia units, “Br II” to “Br IV” (fig. 4) are less heterogeneous than “Br I” because their matrix facies are more voluminous and because the matrix clearly separates the bigger blocks. In both facies, a great diversity of fresh lithologic types such as picritic basalt, olivine-phyric basalt, plagioclase-phyric basalt and aphyric more or less vesicular basalts, gabbro, dunite are found, with no or only few slightly zeolitised blocks. Plurimetric to metric blocks are severely fractured, disintegrated into millimetric to decimetric angular pieces. The frequent polygenic aspect is due to block juxtaposition or imbrication. The abundant matrix is composed of crushed rocks and mineral elements, fine-grained (&lt; mm), showing frequent fluidity and bedding marks (photo 5). The very heterogeneous composition of the matrix is confirmed at a microscopic scale. On the contrary, cores of blocks appear as jigsaw-puzzle-like monolithologic pieces of various basaltic rocks. At their edges, disintegration leads to progressive mixing with neighboring blocks that feed the matrix. Discussion Originality of “Saint-Gilles breccias” “Saint-Gilles breccias” constitute one of the few cases [see also Cantagrel et al., 1999] of debris avalanche deposit outcroppings on the sub-aerial part of an oceanic shield volcano. The main part of the deposit is suspected to be offshore. Their hummocky surface in delineating parallel ridges can be compared to the one described offshore the Grand Brûlé area, east of Piton de la Fournaise [Bachèlery et al., 1996]. “Saint-Gilles breccias” were deposited after several Piton des Neiges flank slide events that were separated by basaltic flows. Repeated debris avalanches have also been proposed to explain Piton de la Fournaise offshore deposits [Lenat et al., 1990 ; Labazuy, 1991]. The occurrence of autochthonous interbedded lava formations is essential to interpret the thick piling up of slide material along Reunion volcano flanks as deposits of repeated avalanches at the same place, instead of as being the products of a single huge event. Many structural and textural features noticed in the upper breccia units reveal crucial information on the emplacement mechanism of debris avalanches. For instance, brecciated blocks are typical of progressive break-up during transport processes. Blocks can simply be fractured, or they can be so severely disintegrated that stretching and mixing with other blocks and matrix formation are observed. The observation of such phenomena implies the existence of numerous percussive events between rocks, as well as internal vibrations in the debris avalanche and therefore the existence of high-speed transport. Lava formations L1 underlying upper breccia units are truncated and strongly striated in a seaward direction (photo 2), parallel to the breccia morphological ridges. In the same way, internal contact surfaces between upper breccia units are shear planes underlain by cataclastic layers and lenses (photo 3). Such structures are interpreted as due to drastic deceleration effects of avalanches reaching a topographic leveling out in the coastal area. This concords with the occurrence of sub-vertical contact areas between the blocks and the matrix. These injections of matrix between the blocks are generated bottom-up from the shear plane at the moment of the sudden deceleration of the avalanche. Other fracture planes that are in accordance with the morphology of ridges, are found in “Br III” unit (see fig. 5). They are interpreted as the result of packing effects. Origin of flank failures Although the source area of breccia formations has not yet been clearly identified, it has to be in the central part of Piton des Neiges as seen in the western cliff of “cirque de Mafate”. Furthermore, “Br I” deeply weathered materials evidently come from the hydrothermalized core of the volcano. Though the “Br I” thickness is not known, the volume involved may be considerable and a part of this volume must constitute the main body of Saint-Gilles offshore deposits. The upper breccias units “Br II” to “Br IV” display very similar textures and lithologies, with dominant non-altered basaltic rocks from the “Phase II” building stage of Piton des Neiges [Billard, 1974]. These units are very thin in the coastal area of Cap La Houssaye (see fig. 2) despite a proximal facies (meaning a deposit in the transport zone nearer than the main deposit zone). They obviously originate from shallow flank slides of restricted extent. We suggest that the upper Saint-Gilles deposits are due to repeated events that produced thin high-speed debris avalanches. Emplacement modalities The morphology of “Saint-Gilles breccias”, or submarine deposits offshore Grand Brûlé (east of Piton de la Fournaise volcano), are typical of sliding movements along shallow depth shear planes (several hundred meters up to two kilometers) within the volcanic pile. But several levels of decollement are suggested by seismic refraction and reflection profiles offshore La Reunion, the deepest corresponding to the top of the preexisting oceanic sediments [de Voogt et al., 1999]. Until now, in Reunion Island, only shallow failures affecting the upper parts of volcanic edifices, with deposits on the lower slopes, have been positively identified. Conditions that trigger giant flank landslides affecting oceanic shields remain poorly understood but we can reasonably speculate that weak hydrothermally-altered layers in the inner part of the volcano favor these gravity-driven processes related to repeated dike injections. The “Saint-Gilles breccia” sequence is considered as a multiphase lateral collapse structure whose first event (“Br I”) was apparently the most voluminous. The corresponding deposit displays frequent hydrothermally-altered material symptomatic of originating from the Piton des Neiges core. Within Piton des Neiges, the low cohesive weathered layer is quite extensive [Nativel, 1978 ; Rançon, 1982] possibly reaching down the volcano flanks [Courteaud et al., 1997]. The interpretative scheme that we propose (fig. 6) in our evaluation of the conditions for the emplacement of Saint-Gilles sequence, takes into account the existence of such a mechanical discontinuity within the volcanic pile. We propose that the massive landslide failure of the west flank of Piton des Neiges volcano that produced the “Br I” breccia, provided efficient channels for younger Piton des Neiges lavas to reach the western and southwestern coastline. Morphological features, as well as radiometric data [Mc Dougall, 1971 ; Gillot and Nativel, 1982] and magnetic surveys [Lénat et al., 2001], yield evidence for preferential accumulation of lava during the last 0.5 m.y. (corresponding mainly to the differentiated series) in this part of the volcano. The relative asymmetry of Piton des Neiges was acquired by rift migration in response to the first huge landslide that produced the “Br I” unit of “Saint-Gilles breccia”, in the manner described by Lipman et al. [1990] for Mauna Loa volcano in Hawaii. The later repetition of flank collapses is consistent with similar structures on other oceanic islands. Since the first lateral collapse, the Piton des Neiges edifice was probably characterized by the existence of an asymmetrical steeper western flank where the old zeolite-rich “Br I” deposits possibly act as a detachment surface for later successive landslides which may have occurred recurrently over a short time interval.

In recent years, low-cost unmanned aerial vehicles (UAVs) photogrammetry and terrestrial laser scanner (TLS) techniques have become very important non-contact measurement methods for obtaining topographic data about landslides. However, owing to the differences in the types of UAVs and whether the ground control points (GCPs) are set in the measurement, the obtained topographic data for landslides often have large precision differences. In this study, two types of UAVs (DJI Mavic Pro and DJI Phantom 4 RTK) with and without GCPs were used to survey a loess landslide. UAVs point clouds and digital surface model (DSM) data for the landslide were obtained. Based on this, we used the Geomorphic Change Detection software (GCD 7.0) and the Multiscale Model-To-Model Cloud Comparison (M3C2) algorithm in the Cloud Compare software for comparative analysis and accuracy evaluation of the different point clouds and DSM data obtained using the same and different UAVs. The experimental results show that the DJI Phantom 4 RTK obtained the highest accuracy landslide terrain data when the GCPs were set. In addition, we also used the Maptek I-Site 8,820 terrestrial laser scanner to obtain higher precision topographic point cloud data for the Beiguo landslide. However, owing to the terrain limitations, some of the point cloud data were missing in the blind area of the TLS measurement. To make up for the scanning defect of the TLS, we used the iterative closest point (ICP) algorithm in the Cloud Compare software to conduct data fusion between the point clouds obtained using the DJI Phantom 4 RTK with GCPs and the point clouds obtained using TLS. The results demonstrate that after the data fusion, the point clouds not only retained the high-precision characteristics of the original point clouds of the TLS, but also filled in the blind area of the TLS data. This study introduces a novel perspective and technical scheme for the precision evaluation of UAVs surveys and the fusion of point clouds data based on different sensors in geological hazard surveys.