Henning Skriver 
  
2 DATA SET 
SAR data from the EMISAR system are used in the project. The Danish airborne EMISAR system is developed at the 
Department of Electromagnetic Systems (EMI) at the Technical University of Denmark. The EMISAR system is a 
fully polarimetric and interferometric SAR (Christensen et al., 1998). It operates at two frequencies, C-band 
(5.3°GHz/5.7°cm wavelength) and L-band (1.25°GHz/24°cm wavelength). The SAR system is flown on a Royal Danish 
Air Force Gulfstream G-3 aircraft. The SAR system is normally operated from an altitude of approximately 12.500°m, 
the spatial resolution is 2°m by 2°m, the ground range swath is approximately 12°km and typical incidence angles range 
from 35 to 60 degrees. The processed data from this system are fully calibrated using an advanced internal calibration 
system. In a new research project at EMI a prototype of a new system with a much better spatial resolution is being 
developed. 
The polarimetric SAR measures the backscattered signal for different combinations of 1) the polarization of the wave 
transmitted from the radar antenna, and 2) the polarization of the receiving antenna. If the transmitted signal is 
horizontally polarized and the receiving antenna also is horizontally polarized, the resulting signal is called HH (H for 
horizontal). Accordingly, the VV signal corresponds to a vertically polarized transmitted signal and a vertically 
polarized receiving antenna. If the transmitting and receiving antennas have different polarizations (i.e. H and V, or V 
and H, respectively) the resulting signal is said to be cross-polarized, i.e. VH or HV, respectively. The backscattering 
coefficient depends on the radar parameters such as frequency, polarization, and incidence angle, and on different 
characteristics of the target, such as the geometrical structure and the dielectric properties. The backscattering 
coefficient for a bare surface depends on the roughness of the surface, i.e. a smooth surface will not backscatter any 
signal toward the radar, whereas a rough surface will scatter the transmitted radar signal in all directions, and part of 
that will be backscattered toward the radar. Consequently, a smooth surface (e.g. a lake in calm wind conditions) will 
appear dark in the SAR image, whereas a rough surface (e.g. a newly ploughed bare field) will appear bright in the 
image. The dielectric properties depend on the composition of the material and the moisture of the target, e.g. a 
ploughed field will appear brighter if the soil moisture is larger. The radar s sensitivity to these properties depends, for 
instance, on the radar wavelength and the polarization of the radar signal. The latter fact is utilized in the polarimetric 
SAR, and the possibility of discrimination between different targets on the ground is improved significantly, when such 
data are available. 
Polarimetric and interferometric SAR data have been acquired by the EMISAR from 1994 to today for a large number 
of scientific applications, such as agricultural crop monitoring, hydrology, monitoring of natural vegetation, studying of 
glacier dynamics, dune dynamics, and sea ice monitoring. In connection with the present project, also urban areas have 
been covered by EMISAR. Aerial photographs are available for an urban as well as a rural area, together with 
appropriate in situ observations. In addition, topographic maps are available in digital form for the two areas. The 
complete data set including multitemporal, multifrequency, polarimetric SAR data and aerial photographs for two years 
has been geometrically corrected to the same map projection. 
3 THEMATIC INFORMATION 
Dependent on the size and shape of the objects different categories of methods may be used for the thematic 
information extraction. Features like roads, buildings, pylons, rivers, etc. may be enhanced and detected using e.g. 
filtering, edge detection, line detection, and point detection methods adapted to the special speckle statistics of SAR 
images and utilizing the multi-frequency, multi-polarization, multi-temporal polarimetric and interferometric SAR 
information. Using the same range of SAR information, methods for detection of classes like forests, lakes, wetlands, 
heath, agricultural areas and urban areas may be applied. In this case, available methods may include traditional 
classification schemes, knowledge-based classifiers, classification based on polarimetric decomposition, interferometric 
correlation, etc. Some methods and results have been reported but further development is strongly needed including 
investigation of the sensitivity to e.g. acquisition time, radar parameters, spatial resolution and environmental 
conditions. In addition, the potential of combining SAR images which are acquired at different radar frequencies, at 
multiple polarizations, and at different times, as well as of combining polarimetric and interferometric data has to be 
investigated further. A very important issue is to study SAR s change detection potential to assist fast, frequent, and 
cost-effective updating of existing map information. Another important aspect is to study the possibility to separate 
between relevant change detection, e.g. a new building, and irrelevant change detection, e.g. from varying 
environmental conditions. 
Below, results of the extraction of thematic information from SAR data are described. In view of the available 
processing techniques, we define three different approaches for information extraction; namely classification and 
  
308 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part Bl. Amsterdam 2000. 
  
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