A three dimensional dominant scatterer map extends the dem information in urban areas

Kurzfassung

The generation of digital elevation models (DEMs) by space-born InSAR is a well-established remote sensing technique. Several application projects as for instance the shuttle radar topography mission (SRTM) have proven the outstanding capability to map the Earth’s surface globally with great accuracy and constant resolution applying this technique. The short mission time of only eleven days guaranteed the homogenous quality of the generated DEM. The typical InSAR-DEM provides a snapshot of the terrain elevation at the time of acquisition including the vegetation cover. A limitation is that the Earth’s cover is mapped only down to a mean radar penetration depth. Polarimetry can be applied to separate volume scattering from the double bounce effect on the ground in forested areas. But in urban areas this scattering model can not be applied. This is in contrast to the great interest in urban areas caused by the high population density and change. Nowadays, the permanent scatterer interferometry which has been invented at POLIMI is working operational and can provide supplementing information. It allows a monitoring of urban areas over time spans of more than ten years. E.g. the subsidence in such spots can be detected and monitored with millimetre accuracy. The separation of the orbit, atmosphere and topography phase effects form the basis for the extreme accuracy regarding the displacement measurement. Furthermore, the PS estimation results in a high precision DEM update at the PS position. The structure of the cities and the radar observation geometry are the reason that this simple elevation concept needs to be extended. It is very likely that more than one dominant scatterer is inside a resolution cell. Tomography can resolve this ambiguity and provides the reflectivity along cross slant range height. Consequently, a real but irregular sampled 3D map of the persistent radar scatterers can be generated which describes the city better. The dominant radar scatterers are related to buildings and other men made features. This is the reason the exact three-dimensional locations of the scatterers provide a lot of useful information on the area and the shape of the city and allowing various applications. Such a 3D map can be a better DEM input for each PS processing that allows an effective PS detection and optimal parameter estimation. A new parametric method for the detection and relative estimation of the two dominant scatterers configuration inside of a resolution cell has been developed. The developed method is more robust because it uses amplitude data only and complements the full tomography which includes the phase information. The city of Munich is one of DLR’s testsite for the PS processing and the developed tomography algorithms. Examples for the generated data set and applications will be shown. The permanent scatterers are assessed in situ and the 3D position of the scatterers is checked and compared to the estimates.