ALOS PRISM Research Articles

Novel comprehensions of lithological and structural features gleaned via Sentinel 2 texture analysis

Detailed geological mapping is the decisive key for mineral deposit prospecting, deciphering tectonic models, and outlining the main framework for most development programs and constructions. Without a doubt, various remote sensing datasets have introduced reliable lithological and structural mapping solutions. The main defect with remote sensing data is the curse of dimensionality, especially with hyperspectral data, where a lot of time is spent handling and selecting representative bands for various geological analyses. Consequently, and for the first time, our research is an attempt to resolve the complicated structural patterns (lineaments, folds, foliations, and cross-cutting relationships) and enhance lithological discrimination using a single band (of Sentinel 2 and ALOS PRISM data) and textural analysis. Through several trials over different pixel sizes (2.5 m and 10 m) and various kernels (3 × 3, 7 × 7, or 11 × 11), reasonable results are obtained, enabling lithological discrimination, in-depth structural analysis (foliations, faults, joints, and folds), shape recognition of systematic rock bodies, and delineation of quaternary deposits using single band analysis rather than time-consuming multiple band processing. Our results have been verified using intensive fieldwork and accurate visual interpretations using different datasets (e.g., previous geological maps, remote sensing data, etc.). Upon field verification and petrographical investigations of this research outcomes, we strongly recommend the adopted approach for the geological community, as it opens the doors for various applications utilizing single-band second-order statistics. We expect that this research could significantly help the geological community by reviving several previous studies and being applicable for future research, besides offering a reasonable approach for minimizing the time and efforts required for detailed field studies by highlighting micro- and mesoscale structures.

Multiscale (microscopic to remote sensing) preliminary exploration of auriferous-uraniferous marbles: A case study from the Egyptian Nubian Shield

Since their recent first record within the Egyptian Nubian Shield, auriferous and uraniferous marbles (Au = 0.98–2.76 g/t; U = 133–640 g/t) have rarely been addressed, despite not only their probable economic importance but also the fact that it is a new genetic style of gold and uranium mineralization in the Nubian Shield rocks. This is mainly attributed to the inadequate localization of these marbles within harsh terrains, as well as the cost and time spent with conventional fieldwork for their identification compared to the main lithological components of the Nubian Shield. On the contrary, remote sensing and machine learning techniques save time and effort while introducing reliable feature identification with reasonable accuracy. Consequently, the current research is an attempt to apply the well-known machine learning algorithm (Support vector Machine—SVM) over Sentinel 2 remote sensing data (with a spatial resolution of up to 10 m) to delineate the distribution of auriferous-uraniferous marbles in the Barramiya-Daghbagh district (Eastern Desert of Egypt), as a case study from the Nubian Shield. Towards better results, marbles were accurately distinguished utilizing ALOS PRISM (2.5 m) pan-sharpened Sentinel 2 data and well-known exposures during fieldwork. With an overall accuracy of more than 90%, a thematic map for auriferous-uraniferous marbles and the major rock units in the Barramiya-Daghbagh district was produced. Marbles are spatially related to ophiolitic serpentinite rocks, as consistent with their genesis within the Neoproterozoic oceanic lithosphere. Field and petrographic investigations have confirmed the newly detected Au and U-bearing zones (impure calcitic to impure dolomitic marbles in Wadi Al Barramiya and Wadi Daghbagh areas and impure calcitic marble in Gebel El-Rukham area). Additionally, X-ray diffraction (XRD), back-scattered electron images (BSEIs), and Energy Dispersive X-ray spectroscopy (EDX) results were integrated to verify our remote sensing results and petrographic investigations. Different times of mineralization are indicated, ranging from syn-metamorphism (gold in Wadi Al Barramiya and Gebel El-Rukham) to post-metamorphism (gold in Wadi Daghbagh and uranium in all locations). Based on the application of geological, mineralogical, machine learning and remote sensing results for the construction of a preliminary exploration model of the auriferous-uraniferous marble in the Egyptian Nubian Shield, we recommend a detailed exploration of Au and U-bearing zones in Barramiya-Dghbagh district and applying the adopted approach to other districts of similar geological environments.

Multisource Data Analysis for Gold Potentiality Mapping of Atalla Area and Its Environs, Central Eastern Desert, Egypt

In this research, airborne geophysical and remote sensing datasets were integrated for gold potentiality mapping (GPM) over the Atalla area in Central Eastern Desert, Egypt. Utilizing aeromagnetic data, detailed structural complexity maps were constructed using the center for exploration targeting (CET) procedure. Then, spectrometric gamma-ray data primarily located hydrothermally altered tracts with discriminating various rock units. The latter are precisely outlined by implementing various techniques (false-color composite (FCC), band ratio (BR), relative absorption band depth (RBD), directed principal component analysis (DPCA), and constrained energy minimization (CEM)) to ASTER, Sentinel 2 and ALOS PRISM datasets, with reference to the geological maps. The study exhibits that gold mineralization is structurally controlled by NW-SE direction. The findings of structural complexity and hydrothermal alteration (argillic, advanced argillic, phyllic, and propylitic) were used as weighted inputs for contouring gold potentiality. The resultant GPM accentuated five gold-promising zones; two are confirmed via locations of ancient gold mines, while the remaining three zones are strongly recommended for their gold potentiality.

ALOS PRISM (AW3D05 STANDARD) and Sentinel-1: Evaluation of New Sources of Digital Elevations Models

Digital Elevation Models (DEM) have many uses and many characteristics that influence choice of model to be used depending on the scale and research objectives. With the advancement of technology, new DEMs have emerged, as well as credible and widespread products such as Sentinel-1 and Advanced Land Observations Satellite World 3D (ALOS AW3D), each with distinct configurations. The height quality evaluation was performed based on Cartographic Accuracy Standard (PEC-PCD) analysis, tendency tests and examination of a profile in a region with rugged relief. A comparison was made with traditional DEM such as SRTM, ALOS PRISM, ALOS PALSAR and ASTER GDEM 2 with new DEMs AW3D Standard and MDS generate from Sentinel-1. The news DEMs have been classified as PEC B at regional scales (1:50,000). The AW3D Standard offers the best result, being rated PEC C for 1:25,000 scale. Another aspect should also be considered, the standard AW3D is capable of presenting more details on the terrain surface, while the DEM from Sentinel-1 SAR data presents a smoothed pattern. Sentinel-1 compared with products of the same spatial resolution, it is concluded that SRTM, ALOS PRISM, ALOS PALSAR products presented superior altimetric accuracy. While that the AW3D, despite the improvement in spatial resolution and altimetric accuracy remained in the same category as the PEC-PCD of the others.

Late Pleistocene slip rate of the Chaman fault based on 10Be exposure dating of offset geomorphic surfaces near Kabul, Afghanistan

We report the first late Pleistocene left-lateral slip rate of the northern Chaman fault in Afghanistan based on 10Be dating of offset alluvial fan surfaces. Field mapping complemented with the analysis of CORONA and ALOS PRISM satellite images and shaded relief and topographic data allows us to identify piercing points across the fault zone at two displaced alluvial fans (Ghat Bandakul and Azadkhail) at Wardak Province south of Kabul. We constrain the ages of offset alluvial fans based on 10Be terrestrial cosmogenic nuclides (TCN) dating of well-embedded quartzite sandstone boulders and cobbles. The Ghat Bandakul alluvial fans are offset at 165 ± 15 m and 235 ± 24 m, for which 10Be TCN model ages average 46.9 ± 3.5 kyr and 66.6 ± 4.9 kyr, respectively, yielding a slip rate of 3.5 ± 0.4 mm/yr. At the Azadkhail site, we identified two offset terraces. Based on 500 ± 50 m offset of a geomorphic surface with 111.2 ± 10.5 kyr age, we obtain a slip rate of 4.5 ± 0.6 mm/yr. Combining the 800 ± 70 m left-lateral offset matching with an average age of 176.8 ± 17.1 kyr for the fan yields the same geomorphic slip rate of 4.5 ± 0.6 mm/yr. These slip rates are considerably lower than geologically, geomorphologically, and geodetically defined slip rates previously obtained along the southern Chaman fault. These results show a clear trend of decreasing fault slip rate with increasing distance to the northeast. The observations suggest that the southern portion of the fault accommodates most of the fault-parallel component of relative motion between the Indian and Eurasian plates. The lower slip rate of the Chaman fault in Afghanistan may be explained by the transfer of the left-lateral shear onto the Gardez and Mokur faults that splay northward from the Chaman fault.

Accuracy assessment of ALOS AW3D30 DSM and comparison to ALOS PRISM DSM created with classical photogrammetric techniques

ABSTRACT In this study the accuracy of ALOS Global Digital Surface Model (AW3D30) with a point spacing of approx. 30-meter mesh was examined, taking as a case study several areas of Greece with complex geomorphologic characteristics. DSMs from ALOS stereo pairs were created using classical photogrammetric techniques. These DSMs were compared with the ALOS AW3D30 and a DEM created from digitized contours. Visual and statistical comparison of the DSMs has been performed.Check Points of known elevation selected from the National Trigonometric Network have been used to estimate the accuracy of the DSMs and the results are presented herein. It has been proved that the freely available AW3D30 DSM presents two or three times lower Root Mean Square Error (RMSE) than the respective DSMs from ALOS PRISM images. In areas with low relief such as Antiparos Island in the Cyclades complex, the ALOS AW3D30 RMSE is only 2.69 m, while in Areas with high relief such as the Chania Prefecture in Western Crete the respective error rises up to 14m. In urban area such as Athens, the capital of Greece, the respective error ranges around 12m due to the complex urban environment (high buildings, narrow urban roads, moving vehicles etc.).

Estimating Water pH Using Cloud-Based Landsat Images for a New Classification of the Nhecolândia Lakes (Brazilian Pantanal)

The Nhecolândia region, located in the southern portion of the Pantanal wetland area, is a unique lacustrine system where tens of thousands of saline-alkaline and freshwater lakes and ponds coexist in close proximity. These lakes are suspected to be a strong source of greenhouse gases (GHGs) to the atmosphere, the water pH being one of the key factors in controlling the biogeochemical functioning and, consequently, production and emission of GHGs in these lakes. Here, we present a new field-validated classification of the Nhecolândia lakes using water pH values estimated based on a cloud-based Landsat (5 TM, 7 ETM+, and 8 OLI) 2002–2017 time-series in the Google Earth Engine platform. Calibrated top-of-atmosphere (TOA) reflectance collections with the Fmask method were used to ensure the usage of only cloud-free pixels, resulting in a dataset of 2081 scenes. The pH values were predicted by applying linear multiple regression and symbolic regression based on genetic programming (GP). The regression model presented an R2 value of 0.81 and pH values ranging from 4.69 to 11.64. A lake mask was used to extract the predicted pH band that was then classified into three lake classes according to their pH values: Freshwater (pH < 8), oligosaline (pH 8–8.9), and saline (≥9). Nearly 12,150 lakes were mapped with those with saline waters accounting for 7.25%. Finally, a trend surface map was created using the ALOS PRISM Digital Surface Model (DSM) to analyze the correlation between landscape features (topography, connection with the regional drainage system, size, and shape of lakes) and types of lakes. The analysis was in consonance with previous studies that pointed out that saline lakes tend to occur in lower positions compared to freshwater lakes. The results open a relevant perspective for the transfer of locally acquired experimental data to the regional balances of the Nhecolândia lakes.

SAR-to-Optical Image Translation Based on Conditional Generative Adversarial Networks—Optimization, Opportunities and Limits

Due to its all time capability, synthetic aperture radar (SAR) remote sensing plays an important role in Earth observation. The ability to interpret the data is limited, even for experts, as the human eye is not familiar to the impact of distance-dependent imaging, signal intensities detected in the radar spectrum as well as image characteristics related to speckle or steps of post-processing. This paper is concerned with machine learning for SAR-to-optical image-to-image translation in order to support the interpretation and analysis of original data. A conditional adversarial network is adopted and optimized in order to generate alternative SAR image representations based on the combination of SAR images (starting point) and optical images (reference) for training. Following this strategy, the focus is set on the value of empirical knowledge for initialization, the impact of results on follow-up applications, and the discussion of opportunities/drawbacks related to this application of deep learning. Case study results are shown for high resolution (SAR: TerraSAR-X, optical: ALOS PRISM) and low resolution (Sentinel-1 and -2) data. The properties of the alternative image representation are evaluated based on feedback from experts in SAR remote sensing and the impact on road extraction as an example for follow-up applications. The results provide the basis to explain fundamental limitations affecting the SAR-to-optical image translation idea but also indicate benefits from alternative SAR image representations.

Analysis Of Land Use In The Southern Part Of Bali Using Fusion Techniques

The southern part of Bali is a central region of tourism, especially in the Sub District of North Kuta, Kuta and South Kuta. The rapid development of tourism is with increasing infrastructure development. Monitor and analyze need to the land use. In this study a fusion technique with HSV method as the combination with ALOS AVNIR-2 2008 and ALOS PRISM in 2008, to estimate of the level of accuracy of image fusion with ALOS AVNIR-2 and subsequent for the analysis of land use in southern part of Bali. Results of the accuracy test with Google Earth showed land use result fusion has high accuracy with overall accuracy of 83. 5%. Analyze of land use showed that significant decrease of moor area in Jimbaran hill, due to rapid development of infrastructure of tourism is very rapid and then extensive residential areas have increased particularly in Sub district of the North Kuta.

Detection of Coastal Damage using Differences in Automatically Generated Digital Surface Models (DSMs): Application to the 2011 Off the Pacific Coast of Tohoku Earthquake Tsunami

Udo, K.; Takeda, Y., and Koshimura, S., 2018. Detection of coastal damage using differences in automatically generated digital surface models (DSMs): Application to the 2011 Off the Pacific Coast of Tohoku Earthquake Tsunami. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 696–700. Coconut Creek (Florida), ISSN 0749-0208.The detection of coastal damage due to the 2011 Off the Pacific Coast of Tohoku Earthquake Tsunami on the southern Sendai Coast was attempted via state-of-the-art remote sensing technology using ALOS PRISM satellite images with a spatial resolution of 2.5 m. Digital surface models (DSMs) were generated semi-automatically, and their accuracies were confirmed via comparisons with digital elevation models generated from aerial laser measurements. The differences between the DSMs prior to and after the tsunami were analyzed statistically for each type of land cover: residential districts, rice fields, coastal forests, and beaches. It was demonstrated that the damage to the coastal forests and residential districts could be detected though the damage in the low land area was difficult to be detected because of its small undulations in topography. Low pass filtering was employed to remove the jitter noise; however, the major characteristics such as damage in the coastal forests and residential areas were not changed by the filtering; that is, the major statistical characteristics could be detected without filtering.

Investigating the use of Alos Prism data in detecting mangrove succession through canopy height estimation

Mangroves have been massively degraded and deforested throughout the world, despite their known ecological and economic values. This study demonstrates the use of ALOS Global Digital Surface Model World (AW3D30) DSM dataset acquired between 2006 and 2011 to map canopy height of different succession stages of mangroves. We employed our previously developed canopy height model for assessing mangrove canopy height in three sites that vary in latitudinal position and mangrove degradation levels, ranging from relatively pristine mangrove ecosystems in Mimika Papua, Indonesia and Sundarbans, Bangladesh to severely degraded mangrove ecosystems in the Mahakam Delta, Indonesia. The study demonstrates good agreement between modeled and measured canopy height from these three sites as indicated by small mean absolute errors of 3.38 m at Mimika, 2.54 m at Sundarbans, and 2.89 m in the Mahakam Delta site. These findings further showed that, in the absence of synthetic aperture radar (SAR) based elevation data (such as SRTM and TanDEM-X), the ALOS PRISM data can be used to map mangrove heights (or in combination with SAR-based elevation data). Our results also pointed out that the ALOS data can differentiate the variability of canopy height estimation between an intact mangrove and severely degraded mangrove ecosystem.

Surface lowering of the debris-covered area of Kanchenjunga Glacier in the eastern Nepal Himalaya since 1975, as revealed by Hexagon KH-9 and ALOS satellite observations

Abstract. This study presents the geodetic mass balance of Kanchenjunga Glacier, one of the largest debris-covered glaciers in the easternmost Nepal Himalaya, which possesses a negative mass balance of −0.18 ± 0.17 m w.e. a−1 for the 1975–2010 study period, estimated using digital elevation models (DEMs) generated from Hexagon KH-9 and ALOS PRISM stereo images. Accurate DEMs, with a relative uncertainty of ±5.5 m, were generated from the intensive and manual editing of triangulated irregular network (TIN) models on a stereo MirrorTM/3D Monitor. The glacier ice-flow velocity field was also calculated using a feature-tracking method that was applied to two ALOS orthoimages taken in 2010. The elevation differences between the two DEMs highlight considerable surface lowering across the debris-covered area, and a slight thickening in the accumulation area of Kanchenjunga Glacier between 1975 and 2010. The magnitude and gradient of surface lowering are similar among the six glacier tributaries, even though they are situated at different elevations, which may reflect variations in the ice-flow velocity field. The pattern of surface lowering correlates well with the ice-flow velocity field over the debris-covered portion of the main tributary, suggesting that the glacier dynamics significantly affect surface lowering by altering the emergence velocity along the glacier, particularly in the compressive ablation area. Surface-lowering patterns partially correspond to the supraglacial pond area fraction of the glacier, with enhanced surface lowering observed in areas that possess a larger pond area fraction. These findings support the hypothesis that supraglacial ponds may intensify ice wastage and play a key role in the heterogeneous surface lowering of debris-covered glaciers. The estimated mass loss of Kanchenjunga Glacier is moderate compared with other debris-covered glaciers in neighboring Himalayan regions, which may be due to the lower pond area fraction of Kanchenjunga Glacier relative to other glaciers.

Accuracy Analysis of DEM Generated from Cokriging Interpolators

DEM as a representation of the earth's surface has many functions for spatial analysis. DEM can be produced from several kinds of techniques such as satellite technology stereo optical or radar technology. Problems when using the optical stereo data is at the high point density level that is not distributed evenly. In regions with homogeneous character, the height point is becoming sparse. This will affect to DEM accuracy. In order to solve the problem, performing fusion techniques using interpolation method cokriging involving data points ALOS PRISM and SRTM height point was conducted. The sparse height point derived from ALOS PRISM on some object is expected to be enhanced by using SRTM data. There were several aspects to enhance the accuracy of DEM-derived from this process: the character of topography, land cover types, density in height point of the data and the precise type of interpolation method used.

Landslide detection using ALOS optical and radar data. A case study from the Ilia prefecture.

In this study the usefulness of the ALOS optical and radar data for landslide monitoring is examined. ALOS contains three sensors, commonly referred to as the “three eyes” of ALOS. These sensors are: the Panchromatic Remote-Sensing Instrument for Stereo Mapping (PRISM), the Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2), and the Phased Array type L-band Synthetic Aperture Radar (PALSAR). The area of study is located in a small village named Sykies near to the city of Andritsena in Western Peloponnese. The area suffered during the last years from enormous fires. As a result many landslides have been recorded. One of the latest Landslides has been recorded on January 2009 as a consequence of heavy rains. That landslide was mapped in situ using differential GPS. The possibility of detecting and mapping the specific landslide using ALOS data is examined in this study and the results are presented. Thirty ALOS radar images within a period of three years, two ALOS Prism data sets and two ALOS AVNIR collected over the same area within a year were used.

Determination of The Water Catchment Area in Semarang City Using a Combination of Object Based Image Analysis (OBIA) Classification, InSAR and Geographic Information System (GIS) Methods Based On a High-Resolution SPOT 6 Image and Radar Imagery

Semarang is the biggest city in central Java-Indonesia which has a rapid and massive infrastructure development nowadays. In order to control water resources and flood, the local goverment has been built east and west flood canal in Kaligarang and West Semarang River. One of main problem in Semarang city is the lack of fresh water in dry season because ground water is not rechargeable well. Rechargeable groundwater ability depends on underground water recharge rate and catchment area condition. The objective of the study is to determine condition and classification of water catchment area in Semarang city. The catchment area conditions will be determine by five parameters as follows soil type, land use, slope, ground water potential and rainfall intensity. In this study, we use three methods approach to solve the problem which is segmentation classification to acquire land use classification from high resolution imagery using nearest neighborhood algorithm, Interferometric Synthetic Aperture Radar (SAR) to derive DTM from SAR Imagery and multi criteria weighting and spatial analysis using GIS method. There are three types optical image (ALOS PRISM, SPOT-6 and ALOS PALSAR) to calculate water catchment area condition in Semarang city. For final result, this research will divide the water catchment into six criteria as follows good, naturally normal, early critical, a little bit critical, critical and very critical condition. The result shows that water catchment area condition is in an early critical condition around 2607,523 Ha (33,17 %), naturally normal condition around 1507,674 Ha (19,18 %), a little bit critical condition around 1452,931 Ha (18,48 %), good with 1157,04 Ha (14,72 %), critical with 1058,639 Ha (13,47 %) and very critical with 75,0387 Ha (0,95 %). The distribution of water catchment area conditions in West and East Flood Canal have an irreguler pattern. In northern area of watershed consists of begin to critical, naturally normal and good condition. Meanwhile in southern area of watershed consists of a little bit critical, critical and very critical condition.

ANALYSIS AND CORRECTION OF SYSTEMATIC HEIGHT MODEL ERRORS

Abstract. The geometry of digital height models (DHM) determined with optical satellite stereo combinations depends upon the image orientation, influenced by the satellite camera, the system calibration and attitude registration. As standard these days the image orientation is available in form of rational polynomial coefficients (RPC). Usually a bias correction of the RPC based on ground control points is required. In most cases the bias correction requires affine transformation, sometimes only shifts, in image or object space. For some satellites and some cases, as caused by small base length, such an image orientation does not lead to the possible accuracy of height models. As reported e.g. by Yong-hua et al. 2015 and Zhang et al. 2015, especially the Chinese stereo satellite ZiYuan-3 (ZY-3) has a limited calibration accuracy and just an attitude recording of 4 Hz which may not be satisfying. Zhang et al. 2015 tried to improve the attitude based on the color sensor bands of ZY-3, but the color images are not always available as also detailed satellite orientation information. There is a tendency of systematic deformation at a Pléiades tri-stereo combination with small base length. The small base length enlarges small systematic errors to object space. But also in some other satellite stereo combinations systematic height model errors have been detected. The largest influence is the not satisfying leveling of height models, but also low frequency height deformations can be seen. A tilt of the DHM by theory can be eliminated by ground control points (GCP), but often the GCP accuracy and distribution is not optimal, not allowing a correct leveling of the height model. In addition a model deformation at GCP locations may lead to not optimal DHM leveling. Supported by reference height models better accuracy has been reached. As reference height model the Shuttle Radar Topography Mission (SRTM) digital surface model (DSM) or the new AW3D30 DSM, based on ALOS PRISM images, are satisfying. They allow the leveling and correction of low frequency height errors and lead to satisfying correction of the DSM based on optical satellite images. The potential of DHM generation, influence of systematic model deformation and possibilities of improvement has been investigated.

ANALYSIS AND CORRECTION OF SYSTEMATIC HEIGHT MODEL ERRORS

The geometry of digital height models (DHM) determined with optical satellite stereo combinations depends upon the image orientation, influenced by the satellite camera, the system calibration and attitude registration. As standard these days the image orientation is available in form of rational polynomial coefficients (RPC). Usually a bias correction of the RPC based on ground control points is required. In most cases the bias correction requires affine transformation, sometimes only shifts, in image or object space. For some satellites and some cases, as caused by small base length, such an image orientation does not lead to the possible accuracy of height models. As reported e.g. by Yong-hua et al. 2015 and Zhang et al. 2015, especially the Chinese stereo satellite ZiYuan-3 (ZY-3) has a limited calibration accuracy and just an attitude recording of 4 Hz which may not be satisfying. Zhang et al. 2015 tried to improve the attitude based on the color sensor bands of ZY-3, but the color images are not always available as also detailed satellite orientation information. There is a tendency of systematic deformation at a Pléiades tri-stereo combination with small base length. The small base length enlarges small systematic errors to object space. But also in some other satellite stereo combinations systematic height model errors have been detected. The largest influence is the not satisfying leveling of height models, but also low frequency height deformations can be seen. <br><br> A tilt of the DHM by theory can be eliminated by ground control points (GCP), but often the GCP accuracy and distribution is not optimal, not allowing a correct leveling of the height model. In addition a model deformation at GCP locations may lead to not optimal DHM leveling. Supported by reference height models better accuracy has been reached. As reference height model the Shuttle Radar Topography Mission (SRTM) digital surface model (DSM) or the new AW3D30 DSM, based on ALOS PRISM images, are satisfying. They allow the leveling and correction of low frequency height errors and lead to satisfying correction of the DSM based on optical satellite images. <br><br> The potential of DHM generation, influence of systematic model deformation and possibilities of improvement has been investigated.

Glacier mass changes in Rongbuk catchment on Mt. Qomolangma from 1974 to 2006 based on topographic maps and ALOS PRISM data

Elevation changes of glacier surfaces were investigated in Rongbuk Catchment (RC) on the northern slopes of Mt. Qomolangma in the central Himalayas, by comparing a digital elevation model (DEM) generated from the 2006 ALOS/PRISM imageries with the base DEM1974 derived from the 1:50,000 topographic maps. The average elevation change rate of glacier surfaces in RC was estimated at −0.47±0.23ma−1 between 1974 and 2006. Such surface lowering rates varied significantly with glaciers and altitudes. One of the notable results is that the debris-covered ice thinned much more rapidly than the exposed ice at higher altitudes. Overall, glaciers in RC have lost mass of −0.06±0.04Gta−1 during 1974–2006. Glacier imbalance constitutes about 50% or more of the Rongbuk runoff.

An assessment of conditions before and after the 1998 Tam Pokhari outburst in the Nepal Himalaya and an evaluation of the future outburst hazard

On 3 September 1998, a glacial lake outburst flood (GLOF) that originated from Tam Pokhari occurred in the Hinku valley of the eastern Nepal Himalaya. This study analyses the lake's geomorphic and hydrologic conditions prior to the outburst, and evaluates the conditions that could contribute to a future flood through photogrammetric techniques. We processed high-resolution Corona KH-4A (2.7 m) and ALOS PRISM (2.5 m) stereo-images taken before and after the GLOF event, and produced detailed topographic maps (2-m contour interval) and DEMs (5 m × 5 m). We (re-) constructed lake water surfaces before (4410 ± 5 m) and after (4356 ± 5 m) the outburst, and reliably estimated the lake water surface lowering (54 ± 5 m) and the water volume released (19.5 ± 2.2 × 106 m3) from the lake, showing good agreement with the results obtained from ground-based measurements. The most relevant conditions that may have influenced the catastrophic drainage of Tam Pokhari in 1998 include the presence of: (i) a narrow (75 ± 6 m), steep (up to 50°) and high (120 ± 5 m) moraine dam; (ii) high lake level (8 ± 5 m of freeboard) and (iii) a steep overhanging glacier (>40°). The lake outburst substantially altered the immediate area, creating a low and wide (>500 m) outwash plain below the lake, a wide lake outlet channel (~50 m) and a gentle channel slope (~3–5°). Our new data suggest that the likelihood of a future lake outburst is low. Our results demonstrate that the datasets produced by photogrammetric techniques provide an excellent representation of micro-landform features on moraine dams, lake water surfaces and the changes in both over time, thereby allowing highly accurate pre- and post-GLOF (volumetric) change analysis of glacial lakes. Furthermore, it enables precise measurement of several predictive variables of GLOFs that can be useful for identifying potentially dangerous glacial lakes or prioritizing them for detailed field investigations. Copyright © 2015 John Wiley & Sons, Ltd.

An improved method to represent DEM uncertainty in glacial lake outburst flood propagation using stochastic simulations

Modelling glacial lake outburst floods (GLOFs) or ‘jokulhlaups’, necessarily involves the propagation of large and often stochastic uncertainties throughout the source to impact process chain. Since flood routing is primarily a function of underlying topography, communication of digital elevation model (DEM) uncertainty should accompany such modelling efforts. Here, a new stochastic first-pass assessment technique was evaluated against an existing GIS-based model and an existing 1D hydrodynamic model, using three DEMs with different spatial resolution. The analysis revealed the effect of DEM uncertainty and model choice on several flood parameters and on the prediction of socio-economic impacts. Our new model, which we call MC-LCP (Monte Carlo Least Cost Path) and which is distributed in the supplementary information, demonstrated enhanced ‘stability’ when compared to the two existing methods, and this ‘stability’ was independent of DEM choice. The MC-LCP model outputs an uncertainty continuum within its extent, from which relative socio-economic risk can be evaluated. In a comparison of all DEM and model combinations, the Shuttle Radar Topography Mission (SRTM) DEM exhibited fewer artefacts compared to those with the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM), and were comparable to those with a finer resolution Advanced Land Observing Satellite Panchromatic Remote-sensing Instrument for Stereo Mapping (ALOS PRISM) derived DEM. Overall, we contend that the variability we find between flood routing model results suggests that consideration of DEM uncertainty and pre-processing methods is important when assessing flow routing and when evaluating potential socio-economic implications of a GLOF event. Incorporation of a stochastic variable provides an illustration of uncertainty that is important when modelling and communicating assessments of an inherently complex process.