TanDEM-X DEM

The TanDEM-X satellite twin mission is a joint effort by German Aerospace Agency (DLR) and the commercial partner AIRBUS Defence and Space to map the Earth’s surface. DLR’s TerraSAR-X and TanDEM-X satellites form a pair of nearly-identical space sensors for interferometric synthetic aperature radar (InSAR) mapping of the Earth’s surface geometry with high precision since 2010. Based on the TanDEM-X radar observations, digital elevation models (DEM) of up to 0.4 arc-seconds resolution (~12 m in North-South direction) have been generated with full global coverage. TanDEM-X DEMs of 0.4 arc-sec resolution are distributed as a commercial product; however for limited areas and localized applications users can apply for DEM data access that is being granted based on the scientific quality and non-commercial character of their project via https://tandemx-science.dlr.de . DLR also plans to freely release the TanDEM-X data set at 3 arc-sec resolution (90 m) to the scientific community; however, full global coverage for the public release is currently not expected due to restrictions posed by the German Satellite Data Security Law (DLR, pers. comm., 2017). It is important to distinguish between the (final) TanDEM-X DEM that is based on multiple data acquisitions, and the intermediate TanDEM-X DEM (also known as IDEM) based on the initial data coverage only. Final products should be preferred over the intermediate results. The absolute vertical accuracy of TanDEM-X elevations is specified with 10 meters or better (at 90% confidence level). A global map of the vertical absolute height error 90% confidence level of each TanDEM-X DEM tile (1°x1° in latitude/longitude) can be seen here . The tile size and longitudinal pixel spacing of the TanDEM-X DEMs varies with geodetic latitude. For instance, between 0° and 50° latitude the data is provided in terms of 1° x 1° tiles (0.4 arc-sec x 0.4 arc-sec or 9001 x 9001 pixels), while for the polar areas the tiles come as 1° x 4° (latitude x longitude, 0.4 arc-sec x 4.0 arc-sec spacings). For each tile up to 9 different information layers are available, e.g., the DEM file itself, (heights), the HEM (height error map), WAM (water indication mask) and COV (coverage mask). Geodetic information: The horizontal datum is WGS84 (World Geodetic System 1984) in its newest realization G1150. Importantly, the vertical datum is also WGS84-G1150. As a result, TanDEM-X elevations refer to the ellipsoid, so are ellipsoidal heights. If physical heights are sought, users need to subtract a geoid model from the ellipsoidal DEM heights. Further notes: As with SRTM, the TanDEM-X DEMs do not represent the bare ground where elevated objects (buildings, vegetation) are present. The producer considers the TanDEM-X DEMs to represent predominantly a Digital Surface Model (DSM), but the elevations do not necessarily represent the top of surface objects. “For example, over forest the X-band SAR scattering center is more located in the upper part of the vegetation volume than on the crown itself, also, dry snow and ice can be penetrated by several meters below the surface.” (DLR, Ground Segment DEM Products Specification Document, version 3.1). Data access: The Homepage of TanDEM-X DEM dataset is available on https://tandemx-science.dlr.de/ . References: DLR, TX-PGS-PL-4003, User License for the Utilisation of TerraSAR-X / TanDEM-X Data and Products for Scientific Use, available on https://tandemx-science.dlr.de/pdfs/TSX-TDX-user-license-v2.2.pdf DLR, TD-PD-PL-0069, TanDEM-X Science Plan, available on https://tandemx-science.dlr.de/pdfs/TD-GS-PL-0069-TanDEM-X-Science-Plan_V1_300610.pdf DLR, TD-GS-PS-0021, DEM Products Specification Document, available on https://tandemx-science.dlr.de/pdfs/TD-GS-PS-0021_DEM-Product-Specification_v3.1.pdf DLR, TD-PD-AO-0033, TanDEM-X DEM Announcement of Opportunity, available on https://tandemx-science.dlr.de/pdfs/TD-PD-AO-0033_DEM_Announcement_of_Opportunity.pdf