Ocean imaging using multichannel along track interferometry

An airborne multichannel along track interferometer (MATI) is described and discussed. This MATI system is based on an X-band SAR installed in a BAE/BAC 1-11 aircraft which can be set up with 2, 3 or 4 beams. It is demonstrated that a MATI can be used to Doppler filter radar signals acquired from a moving platform which are scattered by moving and partially coherent scatterers. Processing techniques are described for the removal of phase errors. These phase errors are caused primarily by the separation of the antennas in range due to the aircraft installation, and by aircraft roll, pitch and yaw motions. The basis of the processing technique is a two stage phase screen which is capable of compensating the differential phase errors between each image in a multichannel set to the precision required for Doppler filtering. It is shown that optimal filtering may be applied to the scattered radar signals by adaptively varying complex weights applied to each channel until an extremum of a selected image measure is obtained. Hence, if a certain type of scatterer is associated with energy located in a particular part of the Doppler spectrum, and an image feature results from the modulation of this type of scatterer, then the visibility of the feature can be maximised using an adaptive MATI. An example is presented showing the technique applied to a sandbank image.