Abstract
Accurate ground control is required to georeferenced airborne and spaceborne images. The production of ortho-photogrammetric data requires ground control that is traditionally provided as Ground Control Points (GCPs) by GNSS measurements in the field. However, it can be difficult to acquire accurate ground control points due to required turn-around time, high costs or impossible access. CompassData, Inc. a specialist in ground control, has expanded its service to deliver Remotely Sensed Ground Control Points (RSGCPs®). TerraSAR-X and TanDEM-X are two satellites with such high accuracy of their orbital positions and SAR data that RSGCPs® can be produced to a sub-meter quality depending on certain parameters and circumstances. The technology and required parameters are discussed in this paper as well as the resulting accuracies.
Highlights
The data collected by the Airbus Space and Defence satellite TerraSAR-X allows to determine an accurate location of single features on the surface of the earth
The primary goal of the test conducted by CompassData, in collaboration with Airbus Space and Defence, was to simulate the workflow in determining RSGCPs® for an inaccessible area anywhere in the world, focusing on standardized man-made features that are found in most parts of the world
The test proved that this extreme mix of variable terrain had no impact on the quality of the RSGCPs
Summary
The data collected by the Airbus Space and Defence satellite TerraSAR-X allows to determine an accurate location of single features on the surface of the earth. A combination of multiple off-nadir viewing angles at a feature sets up an overdetermined solution for its position. Each of the viewing angles provides a SAR range and Doppler equation and satellite position based on highly accurate orbits. In case of a metal pole the signals are combined to a stronger reflection Since these poles are standing vertically the effect adds up for the different ascending and descending passes of the TerraSar-X. The ST scene is less noisy than the HS scene, visible on the asphalt streets and straight lines This can improve the extraction of non-point features like landscape corners and street intersections
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