Most estimates of global mean sea-level rise this century fall below 2 m. This quantity is comparable to the positive vertical bias of the principle digital elevation model (DEM) used to assess global and national population exposures to extreme coastal water levels, NASA’s SRTM. CoastalDEM is a new DEM utilizing neural networks to reduce SRTM error. Here we show – employing CoastalDEM—that 190 M people (150–250 M, 90% CI) currently occupy global land below projected high tide lines for 2100 under low carbon emissions, up from 110 M today, for a median increase of 80 M. These figures triple SRTM-based values. Under high emissions, CoastalDEM indicates up to 630 M people live on land below projected annual flood levels for 2100, and up to 340 M for mid-century, versus roughly 250 M at present. We estimate one billion people now occupy land less than 10 m above current high tide lines, including 230 M below 1 m. Accurate estimates of global mean sea-level rise are important. Here the authors employ a new digital elevation model (DEM) utilizing neural networks and show that the new DEM more than triples the NASA SRTM-based estimates of current global population occupying land below projected sea levels in 2100, with more than 200 million people could be affected based on RCP4.5 and 2 degC of warming.

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New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding.

Large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking. Most moderate‐ and large‐magnitude earthquakes trigger landslides, ranging from small failures in the soil cover to massive, devastating rock avalanches. Some landslides dam rivers and impound lakes, which can collapse days to centuries later, and flood mountain valleys for hundreds of kilometers downstream. Landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows. Cracks and fractures can form and widen on mountain crests and flanks, promoting increased frequency of landslides that lasts for decades. More gradual impacts involve the flushing of excess debris downstream by rivers, which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency, settlements, ecosystems, and infrastructure. Ultimately, earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales. Two recent events have attracted intense research into earthquake‐induced landslides and their consequences: the magnitude M 7.6 Chi‐Chi, Taiwan earthquake of 1999, and the M 7.9 Wenchuan, China earthquake of 2008. Using data and insights from these and several other earthquakes, we analyze how such events initiate processes that change mountain landscapes, highlight research gaps, and suggest pathways toward a more complete understanding of the seismic effects on the Earth's surface.

Earthquake-Induced Chains of Geologic Hazards: Patterns, Mechanisms, and Impacts

High‐resolution raster hydrography maps are a fundamental data source for many geoscience applications. Here we introduce MERIT Hydro, a new global flow direction map at 3‐arc sec resolution (~90 m at the equator) derived from the latest elevation data (MERIT DEM) and water body data sets (G1WBM, Global Surface Water Occurrence, and OpenStreetMap). We developed a new algorithm to extract river networks near automatically by separating actual inland basins from dummy depressions caused by the errors in input elevation data. After a minimum amount of hand editing, the constructed hydrography map shows good agreement with existing quality‐controlled river network data sets in terms of flow accumulation area and river basin shape. The location of river streamlines was realistically aligned with existing satellite‐based global river channel data. Relative error in the drainage area was <0.05 for 90% of Global Runoff Data Center (GRDC) gauges, confirming the accuracy of the delineated global river networks. Discrepancies in flow accumulation area were found mostly in arid river basins containing depressions that are occasionally connected at high water levels and thus resulting in uncertain watershed boundaries. MERIT Hydro improves on existing global hydrography data sets in terms of spatial coverage (between N90 and S60) and representation of small streams, mainly due to increased availability of high‐quality baseline geospatial data sets. The new flow direction and flow accumulation maps, along with accompanying supplementary layers on hydrologically adjusted elevation and channel width, will advance geoscience studies related to river hydrology at both global and local scales. Plain Language Summary Rivers play important roles in global hydrological and biogeochemical cycles, and many socioeconomic activities also depend on water resources in river basins. Global‐scale frontier studies of river networks and surface waters require that all rivers on the Earth are precisely mapped at high resolution, but until now, no such map has been produced. Here we present “MERIT Hydro,” the first high‐resolution, global map of river networks developed by combining the latest global map of land surface elevation with the latest maps of water bodies that were built using satellites and open databases. Surface flow direction of each 3‐arc sec pixel (~90‐m size at the equator) is mapped across the entire globe except Antarctica, and many supplemental maps (such as flow accumulation area, river width, and a vectorized river network) are generated. MERIT Hydro thus represents a major advance in our ability to represent the global river network and is a data set that is anticipated to enhance a wide range of geoscience applications including flood risk assessment, aquatic carbon emissions, and climate modeling.

MERIT Hydro: A High-Resolution Global Hydrography Map Based on Latest Topography Dataset

The primary objective of the TanDEM-X mission is the generation of a global, consistent, and high-resolution digital elevation model (DEM) with unprecedented global accuracy. The goal is achieved by exploiting the interferometric capabilities of the two twin SAR satellites TerraSAR-X and TanDEM-X, which fly in a close orbit formation, acting as an X-band single-pass interferometer. Between December 2010 and early 2015 all land surfaces have been acquired at least twice, difficult terrain up to seven or eight times. The acquisition strategy, data processing, and DEM calibration and mosaicking have been systematically monitored and optimized throughout the entire mission duration, in order to fulfill the specification. The processing of all data has finally been completed in September 2016 and this paper reports on the final performance of the TanDEM-X global DEM and presents the acquisition and processing strategy which allowed to obtain the final DEM quality. The results confirm the outstanding global accuracy of the delivered product, which can be now utilized for both scientific and commercial applications.

Generation and performance assessment of the global TanDEM-X digital elevation model

Endorheic (hydrologically landlocked) basins spatially concur with arid/semi-arid climates. Given limited precipitation but high potential evaporation, their water storage is vulnerable to subtle flux perturbations, which are exacerbated by global warming and human activities. Increasing regional evidence suggests a probably recent net decline in endorheic water storage, but this remains unquantified at a global scale. By integrating satellite observations and hydrological modelling, we reveal that during 2002–2016 the global endorheic system experienced a widespread water loss of about 106.3 Gt yr−1, attributed to comparable losses in surface water, soil moisture and groundwater. This decadal decline, disparate from water storage fluctuations in exorheic basins, appears less sensitive to El Nino–Southern Oscillation-driven climate variability, which implies a possible response to longer-term climate conditions and human water management. In the mass-conserved hydrosphere, such an endorheic water loss not only exacerbates local water stress, but also imposes excess water on exorheic basins, leading to a potential sea level rise that matches the contribution of nearly half of the land glacier retreat (excluding Greenland and Antarctica). Given these dual ramifications, we suggest the necessity for long-term monitoring of water storage variation in the global endorheic system and the inclusion of its net contribution to future sea level budgeting.

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Recent global decline in endorheic basin water storages.

. The Japan Aerospace Exploration Agency (JAXA) generated the global digital elevation/surface model (DEM/DSM) and orthorectified 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. PRISM consisted of three panchromatic radiometers that acquired along-track stereo images. It had a spatial resolution of 2.5 m in the nadir-looking radiometer and achieved global coverage, making it a suitable potential candidate for precise global DSM and ORI generation. In the past 10 years or so, JAXA has conducted the calibration of the system corrected standard products of PRISM in order to improve absolute accuracies as well as to validate the high-level products such as DSM and ORI. In this paper, we introduce an overview of the global DEM/DSM dataset generation project, including a summary of ALOS and PRISM, in addition to the global data archive status. It is also necessary to consider data processing strategies, since the processing capabilities of the level 1 standard product and the high-level products must be developed in terms of both hardware and software to achieve the project aims. The automatic DSM/ORI processing software and its test processing results are also described.

/pdf/precise-global-dem-generation-by-alos-prism-3dwx40graf.pdf

Precise global dem generation by alos prism

. 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.

/pdf/generation-of-the-30-m-mesh-global-digital-surface-model-by-elx9pv9pff.pdf

Generation of the 30 M-MESH global digital surface model by alos prism

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.

https://www.int-arch-photogramm-remote-sens-spatial-inf-sci.net/XLI-B4/157/2016/isprs-archives-XLI-B4-157-2016.pdf

Generation of the 30 m-mesh global digital surface model

深海底の鉱物資源の空間規模把握と成因評価のためには試料の採取および物性計測・化学組成分析が必須である。特に掘削調査により得られる深度方向に連続した試料は，物理探査の有効性評価の観点からも極めて重要である。本研究では海底熱水鉱床の試料情報拡充と潜頭性鉱床に対する自然電位探査の有効性評価を目的とし，潜頭型海底熱水鉱床の胚胎有望地点に対し海底着座型深海用ボーリングシステムによる海底下掘削を実施した。掘削は，熱水兆候と自然電位異常の双方が見られる地域で1点，熱水兆候はあるが自然電位異常のない領域で1点，計2地点で実施された。自然電位異常域で採取されたコアには硫化鉱物の沈殿が確認された一方，自然電位異常の見られない領域で採取されたコアは火山性砕屑物で構成されており，硫化鉱物はほとんど見られなかった。自然電位異常域のコアには詳細な物性計測および化学組成分析が実施された。まず，コア全体に比抵抗測定を実施し，さらにセクションごとに精密なスペクトル誘導分極計測を実施した。また，蛍光Ｘ線分析法による元素濃度分析とＸ線回折分析による鉱物同定も実施し，掘削記載と併せて鉱物分類を行った。その結果，約20 mの範囲に渡る方鉛鉱や黄鉄鉱など導電性硫化鉱物の断続的な産出が明らかとなった。これらの導電性硫化鉱物の濃集地点の分布は，誘導分極効果の強度が高い地点の分布と良く対応することがわかった。一方で高い誘導分極効果の地点と低比抵抗の地点の分布は一致しなかった。以上より，本研究は熱水兆候が必ずしも海底熱水鉱床の胚胎を意味しないこと，自然電位探査が潜頭性鉱床を検出し得ることを示した。また，誘導分極効果が硫化鉱物の検出に役立つことが改めて示され，一方で物理探査による海底熱水鉱床の規模推定には比抵抗だけでは不十分である可能性が示唆された。 

海底熱水活動域において海底着座型掘削装置で取得された掘削試料の物性計測

開発した鉛直電極アレイを用いた電気探査装置の有効性を検証するため，伊是名海穴のHakurei fieldにおいて電気探査装置を無人探査機に搭載した潜航調査を行い，取得したデータを用いて比抵抗構造の推定を行った。測線の北側では複数の低比抵抗域を検出することができ，その低比抵抗域は自然電位の負の異常域と鉛直電場の負の異常域によく一致している。これらの低比抵抗域は，硫化物に伴う低比抵抗異常に相当すると考えられる。一方，南側はほぼ一様構造を示し，目立った異常域は見られなかった。北側の低比抵抗域の間に見られる相対的に高い比抵抗を示す領域は，掘削コアで軽石を含む堆積層が得られている領域であり，両者は整合的である。本装置では，電気探査と同時に複雑な処理なしに鉛直電場として自然電位異常を検出することができる。鉛直電極アレイによる電気探査と自然電位探査を組み合わせることで，より効率的な海底熱水鉱床探査を実施できるようになる。この電気探査装置は海底近傍のフットプリントが小さいため，起伏の激しい地域でも海底近傍を曳航しやすい。鉛直電場を用いた電気探査法は，海底熱水鉱床域での探査に有効な手法となり得る。 

H. Iwamoto

Papers

Precise global dem generation by alos prism

Generation of the 30 M-MESH global digital surface model by alos prism

Generation of the 30 m-mesh global digital surface model

海底熱水活動域において海底着座型掘削装置で取得された掘削試料の物性計測

Resistivity structure deduced from the developed marine vertical DC resistivity survey system around a hydrothermal deposit area