A new strategy combined HASM and classical interpolation methods for DEM construction in areas without sufficient terrain data

Spatial interpolation is an important method in the process of DEM construction. However, DEMs constructed by interpolation methods may induce serious distortion of surface morphology in areas lack of terrain data. In order to solve this problem, this paper proposes a strategy combining high-accuracy surface modeling(HASM) and classical interpolation methods to construct DEM. Firstly, a triangulated irregular network(TIN) is built based on the original terrain data, and the area of the triangles in the TIN is used to determine whether to add supplementary altimetric points(SA-Points). Then, classical interpolation methods, such as Inverse Distance Weighted(IDW) method, Kriging, and Spline, are applied to assign elevation values to the SA-Points. Finally, the SA-Points are merged with the original terrain data, and HASM is used to construct DEM. In this research, two test areas which are located in Nanjing suburb in Jiangsu Province and Guiyang suburb in Guizhou Province are selected to verify the feasibility of the new strategy. The study results show that:(1) The combination of HASM and classical interpolation methods can significantly improve the elevation accuracy of DEMs compared with DEM constructed by a single method.(2) The process of adding SA-Points proposed in this study can be repeated in many times. For the test areas in this paper, compared with the results with only one execution, the results with more executions are in much more accordance with the actual terrain.(3) Among all the methods discussed in this paper, the one combined HASM and Kriging produce the best result. Compared with the HASM alone, absolute mean error(MAE) and root mean square error(RMSE) of the best result were reduced from 1.29 m and 1.83 m to 0.68 m and 0.45 m(the first test area), and from 0.32 m and 0.38 m to 0.21 m and 0.28 m( The second test area).

Vertical accuracy assessment of freely available digital elevation models over low-lying coastal plains

The frequency of coastal flood damages is expected to increase significantly during the twenty-first century as sea level rises in the coastal floodplain.Coastal digital elevation model(DEM)data describing coastal topography are essential for assessing future flood-related damages and understanding the impacts of sea-level rise.The Shuttle Radar Topography Mission(SRTM)and Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model(ASTER GDEM)are currently the most accurate and freely available DEM data.However,an accuracy assessment specifically targeted at DEMs over low elevation coastal plains is lacking.The present study focuses on these areas to assess the vertical accuracy of SRTM and ASTER GDEM using Ice,Cloud,and land Elevation Satellite,Geoscience Laser Altimeter System(ICESat/GLAS)and Real Time Kinematic(RTK)Global Positioning System(GPS)field survey data.The findings show that DEM accuracy is much better than the mission specifications over coastal plains.In addition,optical remote sensing image analysis further reveals the relationship between DEM vertical accuracy and land cover in these areas.This study provides a systematic approach to assess the accuracy of DEMs in coastal zones,and the results highlight the limitations and potential of these DEMs in coastal applications.