Grégoire Leclerc

A simple method to account for topography in the radiometric correction of radar imagery

This article presents a method to study and correct radiometric distortions caused by topography in SAR images. The method is easy to implement and requires neither sophisticated software nor code-level programming. It also considers the case of a flat surface having an elevation different from the one for which calibration parameters were derived. An ortho-image of the slant range distance is used with a Digital Elevation Model to generate images of the local incident angle along the range and azimuth directions. The method compensates for variations in the terrain area of each pixel and for the angular dependence of backscatter, allowing the choice of either an empirical or semi-empirical scattering model. The method is applied to high-resolution C-SAR subsets of an agricultural area in the Central Cordillera of Costa Rica. The removal of topographic features appears excellent for local incident angles up to 80°, but small-scale structures have pronounced effects on the radar return for higher local incident angles and are not adequately corrected.

DÉTERMINATION DE LA RUGOSITÉ DE SURFACE PAR DES MÉTHODES ACCESSIBLES

SUMMARYThis technical note describes two methods for measuring surface roughness and deriving roughness parameters, the first using an inexpensive profilemeter and the second involving a chain and a caliper ruler. The derivation of roughness parameters from surface profiles is described in detail. An analysis conducted with parameters determined for 30 profiles measured in the Canadian Arctic showed that for an approximative characterisation of surface roughness, the chain and ruler method could substitute for the measuring of a profile. There was a high correlation between the maximum height variation in a profile and the RMS height. The correlation length showed a very high coefficient of variation for each type of material sampled, and no tendency to provide different mean values for the different materials.