Evaluation of Cartosat-1 Multi-Scale Digital Surface Modelling Over France

On 5 May 2005, the Indian Space Research Organization launched Cartosat-1, the eleventh satellite of its constellation, dedicated to the stereo viewing of the Earth's surface for terrain modeling and large-scale mapping, from the Satish Dhawan Space Centre (India). In early 2006, the Indian Space Research Organization started the Cartosat-1 Scientific Assessment Programme, jointly established with the International Society for Photogrammetry and Remote Sensing. Within this framework, this study evaluated the capabilities of digital surface modeling from Cartosat-1 stereo data for the French test sites of Mausanne les Alpilles and Salon de Provence. The investigation pointed out that for hilly territories it is possible to produce high-resolution digital surface models with a root mean square error less than 7.1 m and a linear error at 90% confidence level less than 9.5 m. The accuracy of the generated digital surface models also fulfilled the requirements of the French Reference 3D®, so Cartosat-1 data may be used to produce or update such kinds of products

Quantifying Himalayan glacier change from the 1960s to early 2000s, using corona, glims and aster geospatial Data

Since reaching their LIAMs, Himalayan glaciers have generally undergone a period of retreat, evident from large moraines left at former ice limits. Currently, however, detailed assessments of Himalayan glacier fluctuations over the past century are limited and fail to compare spatially or temporally to records available in Central Europe, North America and Scandinavia. Consequently, the variability and magnitude of glacial change across the Himalayas, which is a key indicator of climatic change in this region, is yet to be fully understood. Against a background of poor data availability, Corona imagery and historic GLIMS glacier outlines now offer an opportunity to assess glacier extent for regions of the Himalayas pre-1980. Corona imagery, acquired by a US space-borne reconnaissance mission operational from 1960 to 1970, represents a particularly unique dataset offering high resolution imagery (~1.8 m) with stereo-scopic capabilities. Utilising Corona imagery, there is an opportunity to produce detailed maps of Himalayan glacier extent and extract ice surface elevation estimations, in some instances, for the first time. Despite having been de-classified in 1995, the use of Corona data in the Himalayas has been neglected, mainly because of orthorectification challenges related to its unique geometric distortions. Hence, there remains a need to develop a low cost and easily replicable method of accurately orthorectifying Corona imagery enabling its use as a large-scale glacier mapping tool in the Himalayas. In response to this need, Corona images are orthorectified in this study through the use of: (1) a non-metric photogrammetry approach; and (2) horizontal and vertical reference data acquired from ortho-ASTER imagery and the freely available ASTER GDEM. By comparing glacier measurements derived from Corona imagery, GLIMS data and more contemporary ASTER data, changes in glacier area, length and in some instances volume, between the 1960/70s and early 2000s, were quantified for glaciers selected within four study areas located in Uttarakhand, India and Central Nepal. Importantly, this cross-regional glacier change dataset both complements and enhances current Himalayan records. Most notably, results indicate that glaciers selected in the Bhagirathi and Pindar/Kali basins, Uttarakhand, reduced in area by a relatively small 7.97±0.29% and 7.54±0.26%, respectively. Contrastingly, glaciers selected in the more easterly located Seti and Trisula basins reduced in area by 29.78±0.2% and 50.55±0.08%, respectively. Comparisons of Corona DEM (derived from Corona stereo-pairs) and ASTER Global DEM elevations at the terminus regions of four glaciers revealed extensive surface lowering, ranging from 87±27 m to 142±27 m. For Corona processing, the methods applied were shown to orthorectify Corona images to an accuracy that allows comparable glacier outlines to be delineated, further demonstrating the mapping potential of this dataset. However, for Corona DEM extraction, the use of ASTER spatial control data was shown to be inadequate and the presence of large vertical errors in the DEMs generated hindered the measurement of glacier volume change. For this purpose, it is therefore recommended that the methods developed are tested with the use of very high resolution spatial control data

A pipeline for automated processing of declassified Corona KH-4 (1962-1972) stereo imagery

This study was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (XDA20100300) and the Swiss National Science Foundation (200021E 177652/1) within the framework of the DFG Research Unit GlobalCDA (FOR2630).The Corona KH-4 reconnaissance satellite missions acquired panoramic stereo imagery with high spatial resolution of 1.8–7.5m from 1962-1972. The potential of 800,000+ declassified Corona images has not been leveraged due to the complexities arising from handling of panoramic imaging geometry, film distortions and limited availability of the metadata required for georeferencing of the Corona imagery. This paper presents the Corona Stereo Pipeline (CoSP): A pipeline for processing of Corona KH-4 stereo panoramic imagery. CoSP utilizes deep learning based feature matcher SuperGlue to automatically match features point between Corona KH-4 images and recent satellite imagery to generate Ground Control Points (GCPs). To model the imaging geometry and the scanning motion of the panoramic KH-4 cameras, a rigorous camera model consisting of modified collinearity equations with time-dependent exterior orientation parameters is employed. Using the entire frame of the Corona image, bundle adjustment with well-distributed GCPs results in an average standard deviation or σ0 of less than two pixels. We evaluate fiducial marks on the Corona films and show that pre-processing the Corona images to compensate for film bending improves the 3D reconstruction accuracy. The distortion pattern of image residuals of GCPs and y-parallax in epipolar resampled images suggest that film distortions due to long-term storage likely cause systematic deviations of up to six pixels. Compared to the SRTM DEM, the Corona DEM computed using CoSP achieved a Normalized Median Absolute Deviation of elevation differences of ≈ 4m over an area of approx. 4000km2 after a tile-based fine coregistration of the DEMs. We further assess CoSP on complex scenes involving high relief and glacierized terrain and show that the resulting DEMs can be used to compute long-term glacier elevation changes over large areas.PostprintPeer reviewe

Heterogeneous glacier thinning patterns over the last 40 years in Langtang Himal

Himalayan glaciers are losing mass at rates similar to glaciers elsewhere, but heavily debris-covered glaciers are receding less than debris-free glaciers or even have stable fronts. There is a need for multi-temporal mass balance data to determine if glacier wastage of debris-covered glaciers is accelerating. Here, we present glacier volume and mass changes of seven glaciers (5 partially debris-covered, 2 debris-free) in the upper Langtang catchment in Nepal of 28 different periods between 1974 and 2015 based on 8 digital elevation models (DEMs) derived from high-resolution stereo satellite imagery. We show that glacier volume decreased during all periods between 2006 and 2015 (2006–2015: −0.60 ± 0.34 m a−1) and at higher rates than between 1974 and 2006 (−0.28 ± 0.42 m a−1). However, the behavior of glaciers in the study area was highly heterogeneous, and the presence of debris itself does not seem to be a good predictor for mass balance trends. Debris-covered tongues have highly non-linear thinning profiles, and we show that local accelerations in thinning correlate with complex thinning patterns characteristic of areas with a high concentration of supraglacial cliffs and lakes. At stagnating glacier area near the glacier front, on the other hand, thinning rates may even decrease over time. We conclude that trends of glacier mass loss rates in this part of the Himalaya cannot be generalized, neither for debris-covered nor for debris-free glaciers

Heterogeneous glacier thinning patterns over the last 40 years in Langtang Himal, Nepal

This study presents volume and mass changes of seven (five partially debris-covered, two debris-free) glaciers in the upper Langtang catchment in Nepal. We use a digital elevation model (DEM) from 1974 stereo Hexagon satellite data and seven DEMs derived from 2006–2015 stereo or tri-stereo satellite imagery (e.g., SPOT6/7). The availability of multiple independent DEM differences allows the identification of a robust signal and narrowing down of the uncertainty about recent volume changes. The volume changes calculated over several multiyear periods between 2006 and 2015 consistently indicate that glacier thinning has accelerated with respect to the period 1974–2006. We calculate an ensemble-mean elevation change rate of –0.45ĝ€#x000B1;ĝ€0.18ĝ€mĝ€a−1 for 2006–2015, while for the period 1974–2006 we compute a rate of −0.24ĝ€±ĝ€0.08ĝ€mĝ€a−1. However, the behavior of glaciers in the study area is heterogeneous, and the presence or absence of debris does not seem to be a good predictor for mass balance trends. Debris-covered tongues have nonlinear thinning profiles, and we show that recent accelerations in thinning correlate with the presence of supraglacial cliffs and lakes. At stagnating glacier areas near the glacier front, however, thinning rates decreased with time or remained constant. The April 2015 Nepal earthquake triggered large avalanches in the study catchment. Analysis of two post-earthquake DEMs revealed that the avalanche deposit volumes remaining 6 months after the earthquake are negligible in comparison to 2006–2015 elevation changes. However, the deposits compensate about 40ĝ€% the mass loss of debris-covered tongues of 1 average year.Publisher PDFPeer reviewe

Overall recession and mass budget of Gangotri Glacier, Garhwal Himalayas, from 1965 to 2015 using remote sensing data

Thinning rates for the debris-covered Gangotri Glacier and its tributary glaciers during the period 1968-2014, length variation and area vacated at the snout from 1965 to 2015, and seasonal variation of ice-surface velocity for the last two decades have been investigated in this study. It was found that the mass loss of Gangotri and its tributary glaciers was slightly less than those reported for other debris-covered glaciers in the Himalayan regions. The average velocity during 2006-14 decreased by ~6.7% as compared with that during 1993-2006. The debris-covered area of the main trunk of Gangotri Glacier increased significantly from 1965 until 2015 with the maximum rate of increase (0.8 ± 0.2 km2 a-1) during 2006-15. The retreat (~9.0 ± 3.5 m a-1) was less in recent years (2006-2015) but the down-wasting (0.34 ± 0.2 m a-1) in the same period (2006-2014) was higher than that (0.20 ± 0.1 m a-1) during 1968-2006. The study reinforced the established fact that the glacier length change is a delayed response to climate change and, in addition, is affected by debris cover, whereas glacier mass balance is a more direct and immediate response. Therefore, it is recommended to study the glacier mass balance and not only the glacier extent, to conclude about a glacier's response to climate change.Publisher PDFPeer reviewe

The glaciers climate change initiative: Methods for creating glacier area, elevation change and velocity products

Glaciers and their changes through time are increasingly obtained from a wide range of satellite sensors. Due to the often remote location of glaciers in inaccessible and high-mountain terrain, satellite observations frequently provide the only available measurements. Furthermore, satellite data provide observations of glacier character- istics that are difficult to monitor using ground-based measurements, thus complementing the latter. In the Glaciers_cci project of the European Space Agency (ESA), three of these characteristics are investigated in detail: glacier area, elevation change and surface velocity. We use (a) data from optical sensors to derive glacier outlines, (b) digital elevation models from at least two points in time, (c) repeat altimetry for determining elevation changes, and (d) data from repeat optical and microwave sensors for calculating surface velocity. For the latter, the two sensor types provide complementary information in terms of spatio-temporal coverage. While (c) and (d) can be generated mostly automatically, (a) and (b) require the intervention of an analyst. Largely based on the results of various round robin experiments (multi-analyst benchmark studies) for each of the products, we suggest and describe the most suitable algorithms for product creation and provide recommendations concerning their practical implementation and the required post-processing. For some of the products (area, velocity) post-processing can influence product quality more than the main-processing algorithm

Surge-type glaciers in the Tien Shan (Central Asia)

Surge-Type glaciers have been observed in several mountain ranges of the world. Though Karakoram and Pamir are the hot spots for the occurrence of surge-Type glaciers in High Mountain Asia, few surge-Type glaciers also exist in Tien Shan. These have not been studied or reported in detail in the recent literature. We have identified 39 surge-Type glaciers and five tributary surges in Tien Shan either from available literature or by visual interpretation using available images from the period 1960 until 2014. Out of the 39 glaciers, 9 are confirmed as surge-Type, 13 are very probably surge-Type, and the remaining are possibly of surge-Type. Most of the surge-Type glaciers are located in Ak-Shiirak and Central Tien Shan. Compared with the normal glaciers of Tien Shan, the surge-Type glaciers are larger, cover higher ranges of elevations, and have shallower slopes. There is no significant difference in aspect. The largest surge events were observed in Central Tien Shan: North Inylchek Glacier (years 1996/1997) and Samoilowich Glacier (years 1992 until 2006) advanced several kilometers. The surge cycle was around 50 years for both of these glaciers. The advance was less pronounced for all other surge-Type glaciers during the period ca. 1960-2014. Some of the tributary glaciers behaved differently than the main glaciers in the sense that they continuously advanced during the entire period of our study, whereas the main glaciers have remained stable or retreated.Publisher PDFPeer reviewe