The main shock of the 2015 Gorkha Earthquake in Nepal induced numerous avalanches, rockfalls, and landslides in Himalayan mountain regions. A major village in the Langtang Valley was destroyed and numerous people were victims of a catastrophic avalanche event, which consisted of snow, ice, rock, and blast wind. Understanding the hazard process mainly depends on limited witness accounts, interviews, and an in situ survey after a monsoon season. To record the immediate situation and to understand the deposition process, we performed an assessment by means of satellite-based observations carried out no later than 2 weeks after the event. The avalanche-induced sediment deposition was delineated with the calculation of decreasing coherence and visual interpretation of amplitude images acquired from the Phased Array-type L-band Synthetic Aperture Radar-2 (PALSAR-2). These outline areas are highly consistent with that delineated from a high-resolution optical image of WorldView-3 (WV-3). The delineated sediment areas were estimated as 0.63 km(2) (PALSAR-2 coherence calculation), 0.73 km(2) (PALSAR-2 visual interpretation), and 0.88 km(2) (WV-3). In the WV-3 image, surface features were classified into 10 groups. Our analysis suggests that the avalanche event contained a sequence of (1) a fast splashing body with an air blast, (2) a huge, flowing muddy mass, (3) less mass flowing from another source, (4) a smaller amount of splashing and flowing mass, and (5) splashing mass without flowing on the east and west sides. By means of satellite-derived pre-and post-event digital surface models, differences in the surface altitudes of the collapse events estimated the total volume of the sediments as 5.51 +/- 0.09 +/- 10(6) m(3), the largest mass of which are distributed along the river floor and a tributary water stream. These findings contribute to detailed numerical simulation of the avalanche sequences and source identification; furthermore, altitude measurements after ice and snow melting would reveal a contained volume of melting ice and snow.

To better understand the influence of topography on the formation of Himalayan debris-covered glaciers, we manually digitized 5301 glaciers, covering an area of 5691 +/- 893 km(2), from high-resolution Advanced Land Observing Satellite imagery, and identified 842 debris-covered glaciers with a debris-covered area of 3839 +/- 753 km(2). This estimation of the debris-covered area of these glaciers is a novel approach in the Eastern Himalayas. We investigated the relationship between the debris-covered area and the corresponding potential debris supply (PDS) slopes for the debris-covered glaciers across the region. The PDS slopes on the southern side show better correlation with their debris-covered area formation than those situated on the northern side of the Himalayan barrier, with this correlation weakening toward the western massifs. Further investigation showed that PDS slopes oriented SE to Wexert a stronger control on the formation of debris-covered areas, which is related to the diurnal freezeethaw cycle on the southern slope of the mountain barrier. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.

Topographical information is fundamental to many geo-spatial related information and applications on Earth. Remote sensing satellites have the advantage in such fields because they are capable of global observation and repeatedly. Several satellite-based digital elevation datasets were provided to examine global terrains with medium resolutions e.g. the Shuttle Radar Topography Mission (SRTM), the global digital elevation model by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER GDEM). A new global digital surface model (DSM) dataset using the archived data of the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) onboard the Advanced Land Observing Satellite (ALOS, nicknamed "Daichi") has been completed on March 2016 by Japan Aerospace Exploration Agency (JAXA) collaborating with NTT DATA Corp. and Remote Sensing Technology Center, Japan. This project is called "ALOS World 3D" (AW3D), and its dataset consists of the global DSM dataset with 0.15 arcsec. pixel spacing (approx. 5 m mesh) and ortho-rectified PRISM image with 2.5 m resolution. JAXA is also processing the global DSM with 1 arcsec. spacing (approx. 30 m mesh) based on the AW3D DSM dataset, and partially releasing it free of charge, which calls "ALOS World 3D 30 m mesh" (AW3D30). The global AW3D30 dataset will be released on May 2016. This paper describes the processing status, a preliminary validation result of the AW3D30 DSM dataset, and its public release status. As a summary of the preliminary validation of AW3D30 DSM, 4.40 m (RMSE) of the height accuracy of the dataset was confirmed using 5,121 independent check points distributed in the world.

Advanced Land Observing Satellite-2 (ALOS-2, "DAICHI-2") performed various emergency observation with its Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) in Asia in 2015. Especially for corresponding to the emergency request from Sentinel Asia related to the Mw 7.8 Gorkha Nepal Earthquake 2015, PALSAR-2 successfully detected not only the crustal deformation but also the avalanches and local displacements. In this presentation, we describe these performances, analysis and the other emergency observations.

One of the main missions of the Advanced Land Observing Satellite-2 (ALOS-2, "DAICHI-2") is the disaster monitoring. Japan Aerospace Exploration Agency (JAXA) has operated the emergency observation more than hundred times in 2015. Not only the most important event in 2015, the Mw 7.8 Gorkha earthquake on April 25, the Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) aboard ALOS-2 observed various floods, volcano eruptions and earthquakes. In this paper, we present some emergency observation results which were impossible to be performed by the previous ALOS. That is, automatically burst aligned ScanSAR to ScanSAR interferometry and, left / right looking for increasing acquisition opportunity.

<p>Rapid and all-weather detection of flood areas is needed to monitor and mitigate flood disasters. This study addressed flood area detection using ALOS-2 PALSAR-2 data acquired during the 2015 heavy rainfall disaster in the Kanto and Tohoku area of Japan. We propose an approach to flood area detection by thresholding amplitude and interferometric coherence images for non-urban and urban areas, respectively. PALSAR-2-derived flood areas were validated using the inundation map provided by the Geospatial Information Authority of Japan (GSI) and showed 75% accuracy and a 0.51 kappa coefficient in flood/non-flood discrimination. The effectiveness of a lower incidence angle (less than 40 degrees) and a high-sensitivity observation mode (6-m resolution mode) for detecting non-urban flooding was also demonstrated by a comparative study. Interferometric phase variation was revealed to be more effective in detecting urban flooding than conventional interferometric coherence. Our results demonstrate the feasibility of PALSAR-2 for rapid flood monitoring and can be used as a reference for possible future flood disasters.</p>

To better understand the recent wide-scale changes in glacier coverage, we created and compared two glacier inventories covering eastern Nepal, based on aerial photographs (1992) and high-resolution Advanced Land Observing Satellite (ALOS) imagery (2006-10). The ALOS-derived inventory contained 1034 debris-free and 256 debris-covered glaciers with total and average areas of 440.2 +/- 33.3 and 0.42 km(2) and 1074.4 +/- 206.4 and 4.19 km(2), respectively. We found that the debris-free glaciers have lost 11.2% (0.7 +/- 0.1% a(-1)) of their area since 1992, whereas the number of glaciers increased by 5% because of fragmentation. The area change was significantly correlated by simple linear regression with minimum elevation (r = 0.30), maximum elevation (r = -0.18), altitudinal range (r = -0.50), glacier area (r = -0.62) and mean slope (r = 0.16), confirming that larger glaciers tended to lose a larger area (but a smaller percentage) than smaller glaciers. The infra-regional analysis of the glacier changes clearly showed higher shrinkage rates in the western massifs compared with the eastern massifs. In addition, 61 small glaciers covering an area of 2.4 km(2) have completely disappeared since 1992.

Digital glacier inventories are invaluable data sets for revealing the characteristics of glacier distribution and for upscaling measurements from selected locations to entire mountain ranges. Here, we present a new inventory of Advanced Land Observing Satellite (ALOS) imagery and compare it with existing inventories for the Bhutan Himalaya. The new inventory contains 1583 glaciers (1487 +/- 235 km(2)), thereof 219 debris-covered glaciers (951 +/- 193 km(2)) and 1364 debris-free glaciers (536 +/- 42 km(2)). Moreover, we propose an index for quantifying consistency between two glacier outlines. Comparison of the overlap ratio demonstrates that the ALOS-derived glacier inventory contains delineation uncertainties of 10-20% which depend on glacier size, that the shapes and geographical locations of glacier outlines derived from the fourth version of the Randolph Glacier Inventory have been improved in the fifth version, and that the latter is consistent with other inventories. In terms of whole glacier distribution, each data set is dominated by glaciers of 1.0-5.0 km(2) area (31-34% of the total area), situated at approximately 5400m elevation (nearly 10% in 100m bin) with either north or south aspects (22 and 15 %). However, individual glacier outlines and their area exhibit clear differences among inventories. Furthermore, consistent separation of glaciers with inconspicuous termini remains difficult, which, in some cases, results in different values for glacier number. High-resolution imagery from Google Earth can be used to improve the interpretation of glacier outlines, particularly for debris-covered areas and steep adjacent slopes.

The Japan Aerospace Exploration Agency is generating the global digital elevation/surface model (DEM/DSM) and ortho-rectified image (ORI) using the archived data of the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) onboard the Advanced Land Observing Satellite (ALOS, nicknamed 'Daichi'), which was operated from 2006 to 2011. The overview and the processing status of the global DSM/ORI dataset generation project called 'ALOS World 3D' (AW3D) is introduced in this paper. It is necessary to consider data processing strategies, since the processing capabilities of the level 1 standard product and AW3D products must be developed both hardware and software to achieve the project aims. The processing strategies and an initial validation of generated DSM dataset are described. As an initial validation results, 4.10 m of height accuracy as root mean square error was confirmed. The generation and distribution of a lower resolution AW3D DSM dataset is also introduced.

© Author(s) 2015. CC Attribution 3.0 License. We present a new glacier inventory for high-mountain Asia named "Glacier Area Mapping for Discharge from the Asian Mountains" (GAMDAM). Glacier outlines were delineated manually using 356 Landsat ETM+ scenes in 226 path-row sets from the period 1999-2003, in conjunction with a digital elevation model (DEM) and high-resolution Google EarthTM imagery. Geolocations are largely consistent between the Landsat imagery and DEM due to systematic radiometric and geometric corrections made by the United States Geological Survey. We performed repeated delineation tests and peer review of glacier outlines in order to maintain the consistency and quality of the inventory. Our GAMDAM glacier inventory (GGI) includes 87 084 glaciers covering a total area of 91 263 ± 13 689 km2 throughout high-mountain Asia. In the Hindu Kush-Himalaya range, the total glacier area in our inventory is 93% that of the ICIMOD (International Centre for Integrated Mountain Development) inventory. Discrepancies between the two regional data sets are due mainly to the effects of glacier shading. In contrast, our inventory represents significantly less surface area ('24%) than the recent global Randolph Glacier Inventory, version 4.0 (RGI), which includes 119 863 ± 9201 km2 for the entirety of high Asian mountains. Likely causes of this disparity include headwall definition, effects of exclusion of shaded glacier areas, glacier recession since the 1970s, and inclusion of seasonal snow cover in the source data of the RGI, although it is difficult to evaluate such effects quantitatively. Further rigorous peer review of GGI will both improve the quality of glacier inventory in high-mountain Asia and provide new opportunities to study Asian glaciers.

Among meteorological elements, precipitation has a large spatial variability and less observation, particularly in high-mountain Asia, although precipitation in mountains is an important parameter for hydrological circulation. We estimated precipitation contributing to glacier mass at the median elevation of glaciers, which is presumed to be at equilibrium-line altitude (ELA) such that mass balance is zero at that elevation, by tuning adjustment parameters of precipitation. We also made comparisons between the median elevation of glaciers, including the effect of drifting snow and avalanche, and eliminated those local effects. Then, we could obtain the median elevation of glaciers depending only on climate to estimate glacier surface precipitation. The calculated precipitation contributing to glacier mass can elucidate that glaciers in arid high-mountain Asia receive less precipitation, while much precipitation makes a greater contribution to glacier mass in the Hindu Kush, the Himalayas, and the Hengduan Shan due to not only direct precipitation amount but also avalanche nourishment. We classified glaciers in high-mountain Asia into summer-accumulation type and winter-accumulation type using the summer-accumulation ratio and confirmed that summer-accumulation-type glaciers have a higher sensitivity than winter-accumulation-type glaciers.

To understand the formation conditions of debris-covered glaciers, we examined the dimension and shape of debris-covered areas and potential debris-supply (PDS) slopes of 213 glaciers in the Bhutan Himalaya. This was undertaken using satellite images with 2.5m spatial resolution for manual delineation of debris-covered areas and PDS slopes. The most significant correlation exists between surface area of southwest-facing PDS slopes and debris-covered area. This result suggests that the southwest-facing PDS slopes supply the largest quantity of debris mantle. The shape of debris-covered areas is also an important variable, quantitatively defined using a geometric index. Elongate or stripe-like debris-covered areas on north-flowing glaciers are common throughout the Bhutan Himalaya. In contrast, south-flowing glaciers have large ablation zones, entirely covered by debris. Our findings suggest that this difference is caused by effective diurnal freeze-thaw cycles rather than seasonal freeze-thaw cycles, permafrost degradation, or snow avalanches. In terms of geographic setting, local topography also contributes to glacier debris supply and the proportion of debris cover on the studied glaciers is suppressed by the arid Tibetan climate, whereas the north-to-south asymmetric topography of the Bhutan Himalaya has less influence on the proportion of debris cover.

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