ASTER Elevation Research Articles

Quantifying Geodetic Mass Balance of the Northern and Southern Patagonian Icefields Since 1976

Southern Andean glaciers contribute substantially to global sea-level rise. Unfortunately, mass balance estimates prior to 2000 are limited, hindering our understanding of the evolution of glacier mass changes over time. Elevation changes over 1976/1979 to 2000 derived from historical KH-9 Hexagon imagery and NASADEM provide the basis for geodetic mass balance estimates for subsets of the Northern Patagonian Icefield (NPI) and the Southern Patagonian Icefield (SPI), extending current mass balance observations by ∼20 years. Geodetic mass balances were −0.63 ± 0.03 m w.e. yr−1 for 63% of the NPI and −0.33 ± 0.05 m w.e. yr−1 for 52% of the SPI glacierized areas for this historical period. We also extend previous estimates temporally by 25% using NASADEM and ASTER elevation trends for the period 2000 to 2020, and find geodetic mass balances of −0.86 ± 0.03 m w.e. yr−1 for 100% of the NPI and −1.23 ± 0.04 m w.e. yr−1 for 97% of the SPI glacierized areas. 2000–2020 aggregations for the same areas represented in the 1976/1979 to 2000 estimates are −0.78 ± 0.03 m w.e. yr−1 in the NPI and −0.80 ± 0.04 m w.e. yr−1 on the SPI. The significant difference in SPI geodetic mass balance in the modern period for 100% vs. 52% of the glacierized area suggests subsampling leads to significant biases in regional mass balance estimates. When we compare the same areas in each time period, the results highlight an acceleration of ice loss by a factor of 1.2 on the NPI and 2.4 on the SPI in the 21st century as compared to the 1976/1979 to 2000 period. While lake-terminating glaciers show the most significant increase in mass loss rate from 1976/1979–2000 to 2000–2020, mass balance trends are highly variable within glaciers of all terminus environments, which suggests that individual glacier sensitivity to climate change is dependent on a multitude of morphological and climatological factors.

Which heterogeneous glacier melting patterns can be robustly observed from space? A multi-scale assessment in southeastern Tibetan Plateau

Region-wide investigation of glacier change in High Mountain Asia marked the strongest recession in southeastern Tibetan Plateau (SETP) in recent decades. However, evident differences of quantitative glacier mass balance (MB) estimations on fine scales exist in the prior reports. The large uncertainties in current geodetic observations over this region highlight the need for more independent validations and investigations on the spatial variability of glacier change. This study enriched glacier MB estimates over the SETP by using the newly released global Digital Elevation Model (DEM) - the TanDEM-X and analyzed the spatial pattern of glacier change on multi-spatial scales by comparing available satellite-based geodetic observations. Results reveal that the TanDEM-X - SRTM elevation differences, which show no obvious horizontal shifts and no significant elevation-dependent bias, provide reliable elevation change information over this challenging area. On the regional scale, the geodetic datasets (the ASTER elevation change rates data, TanDEM-X- SRTM differences, ICESat) achieved a highly consistent estimate of glacier MB at −4.11 ± 1.52 Gt a−1 (−0.60 ± 0.16 m w.e. a−1) during 2000 and 2010s. On the subregional scale, the two gridded geodetic datasets revealed a clear contrast between moderate thinning of spring-accumulation type glaciers in the south and significantly more negative glacier MB of summer-accumulation type glaciers in the north. Glacier-wide MB showed high heterogeneity, which was closely related to the combined effect of topographic variation and climate forcings. We observed similar glacier thinning rates between debris-covered land-terminating glaciers and clean-ice glaciers (−0.50 ± 0.32 m w.e. a−1) but remarkable more negative MB (−0.89 ± 0.36 m w.e. a−1) of debris-covered glaciers connected with glacial lakes, which may indicate different evolution process of debris-covered glaciers in the monsoon-influenced region. This study demonstrates that current satellite-based geodetic observations achieve overall consistent patterns of glacier mass changes even over the most challenging mountainous areas (complicated terrain and climate). With the global TanDEM-X DEM and increasing observations from the mission, we expect improved consistency in glacier MB estimation on large spatial scales as well as detailed investigation of glacier mass change variability in the future.

Performance evaluation and sensitivity analysis of ASTER and SRTM (30m) DEM derived terrain variables in landslide susceptibility assessment: a case from the Western Ghats

Performance and sensitivity of freely available equal resolution space borne digital elevation model derivatives in landslide susceptibility analysis were carried out in a selected part of the Western Ghats, India. ASTER and SRTM digital elevation models having 30m resolution were used to derive the terrain variables such as slope, aspect, relative relief, slope length and steepness, curvature, landform and stream networks. Most of the variables shown spatial variability in distribution pattern, which affects the results of geo-environmental processes analyzed. Sensitivity and performance of each variable derived from the digital elevation models were assessed by preparing a landslide susceptibility index (LSI) maps using the Information Value (InfoVal) technique and was validated through receiver operator characteristics (ROC) curve analysis. LSI maps generated point towards the capability of the SRTM digital elevation model, to correctly generate the terrain variables than the ASTER elevation surface, by giving the accuracy of LSI maps greater than those produced using the ASTER derived parameters (0.77 and 0.72 for SRTM; 0.67 and 0.65 for ASTER). The results of the present study suggest, the SRTM digital elevation data is more sensitive and suitable for terrain analysis and earth surface process modelling than the ASTER elevation data sets, though both possess equal resolutions .DOI: http://dx.doi.org/10.5755/j01.erem.73.2.16385

Comparison and Suitability of SRTM and ASTER Digital Elevation Data for Terrain Analysis and Geomorphometric Parameters: Case Study of Sungai Patah Subwatershed (Baram River, Sarawak, Malaysia)

Determination of suitability of satellite-derived elevation data sets in terrain characterisation in a tropical region was carried out on the Sungai Patah subwatershed in the interior of Sarawak, East Malaysia. The goal was to facilitate rapid assessment of topographic variables and spatial parameters related to the morphometric aspects of the region. The freely available SRTM (90 m) and ASTER (30 m) elevation data sets were compared and used to generate spatial and aspatial parameters. The cross-validation of SRTM and ASTER elevation surfaces with toposheet-derived elevation for 200 random points shows root mean squared errors (RMSE) of ± 35.08 m and ± 44 m, respectively. The spatial and aspatial parameters derived show certain major and minor variations in the outputs, which can be attributed to the differences in spatial and spectral resolutions of the data acquisition systems. The results and the findings of the present study suggest that both SRTM and ASTER elevation data sets can be used for terrain characterisation in regions similar to the study area, by replacing the traditional toposheet-derived elevation surfaces. However, minor errors are present when either set is used independently. This can be avoided by the concurrent use of SRTM and ASTER elevation data sets, which will reduce data errors and artefacts in both data sets and improve the accuracy of terrain variables and watershed parameters derived from them. DOI: http://dx.doi.org/10.5755/j01.erem.71.3.12566

Accuracy of SRTM-X and ASTER Elevation Data and its Influence on Topographical and Hydrological Modeling: Case Study of the Pieniny Mts. in Poland

Satellite sensors provide currently reliable elevation data over large areas, with spatial resolutions below 100 m and reported accuracies of approximately 10 m. However, the vertical accuracy of these quasi-global digital elevation models (DEM) varies depending on the terrain and land cover, decreasing in mountain areas, and may influence the quality of products derived from these data, like stream channel network or relief forms. In this paper, we investigated two global elevation data sets: SRTM-X DEM and ASTER GDEM, assessing their vertical accuracy and reliability of terrain features extracted automatically from the elevation data. The research was carried out in the Pieniny Mts., a small mountain range in southern Poland, with elevations ranging from about 400 m to 1000 m a.s.l. One particular attribute of this mountain range that may create several problems in deriving accurate terrain features is a deep, narrow and windy gorge of the Dunajec river. We found that the vertical accuracy of SRTM-X DEM is significantly better than of the ASTER GDEM (Root Mean Square errors of 12.05 m and 17.43 m, respectively). Both DEMs allow to extract terrain features with a similar accuracy in areas of moderately steep and gentle slopes, yet fail to properly represent the floor of the Dunajec gorge as relative vertical errors along the river may exceed 100 m. Therefore, we conclude that while both models provide statistically reliable description of the terrain surface, they require additional corrections for hydrological or terrain modeling.

Morphometric Analysis of Kangshabati-Darkeswar Interfluves Area in West Bengal, India using ASTER DEM and GIS Techniques

The aim of the study is to delineate the morphometric characteristics of Kangshabati-Darkeswar Interfluves Area using remote sensing and GIS technology. 10 km2 grids were elaborate to delineate the relief characteristics using Advance Space Thermal Emission and Radiometer (ASTER) data. Drainage networks were automatically extracted from digital aster elevation models. Second order local polynomial (LP) interpolation technique was used to estimate the surface characteristics of the study area using ArcGIS 9.3. The absolute elevation of the study region is extended between 4.0-949.29 m with an average elevation of 484.50 m. The highest relative relief resulted 833.69 m, whereas the average ruggedness index of the study area is recorded as 0.09 per 10 km2 area. The average drainage density of the study area was computed 0.73/sq. km and the highest drainage intensity are recorded as 9.58/10 km2 grid area. The average length of overland flow of the study area was 2.56/10 km2 grid areas. The result of the study highlights an about the spatial distribution of relief and hydrological characteristics which may provide the knowledge to devise and accomplish an appropriate plan to progress agriculture and others allied activities. Hence, from the study, it can be concluded that remote sensing data (ASTER –DEM) coupled with GIS techniques prove to be a competent tool in morphometric analysis and the data can be used for basin or interfluves area management and other hydrological studies in future.

Effect of the difference between surface and terrain models on gravity field related quantities

Topographic masses have a strong impact on the medium and short wavelength components of the gravitational signal generated by the mass of the Earth, thus digital terrain models (DTM) are routinely involved in gravity field modelling. In this study the verification of the Shuttle Radar Topographic Mission (SRTM) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) which is a joint product of METI (Ministry of Economy, Trade and Industry of Japan) and NASA has been done by comparing them to the points of the horizontal and vertical control networks of Hungary. SRTM data fit better to geodetic ground control points than ASTER GDEM, since some artefacts have been found in ASTER elevation set which impede further use of the latter without any pre-processing. Since SRTM is an “unclassified” surface model including all those points which reflected the scanning radar signal thus tree canopy height has been compared to the differences of SRTM and DTM elevations in a hilly test area in Hungary where a local and accurate DTM having 20 m × 20 m horizontal resolution was available. Considerable agreement was indicated between forest height and model differences. Model differences were evaluated to determine their effect synthetically on gravity related quantities. Their influence on geoid height is insignificant, but the change of the investigated second derivatives of the potential is considerable.