Abstract
Ground-based tomographic radar measurements provide valuable knowledge about the electromagnetic scattering mechanisms and temporal variations of an observed scene and are essential in preparation for space-borne tomographic synthetic aperture radar (SAR) missions. Due to the short range between the radar antennas and a scene being observed, the tomographic radar observations are affected by several systematic errors. This article deals with the modelling and calibration of three systematic errors: mutual antenna coupling, magnitude and phase errors and the pixel-variant impulse response of the tomographic image. These errors must be compensated for so that the tomographic images represent an undistorted rendering of the scene reflectivity. New calibration methods were described, modelled and validated using experimental data. The proposed methods will be useful for future ground-based tomographic radar experiments in preparation for space-borne SAR missions.
Highlights
Radar tomography is a remote sensing technique for acquiring a rendering of the threedimensional radar reflectivity of a scene
The calibration procedure changes the intensity distribution in the image, but does not result in a horizontally-homogeneous intensity distribution. This is because of image speckle, different incidence angles and canopy attenuation at different ground ranges, which are not system effects. These results demonstrate that the pixel-variant bias has been compensated for and that the proposed calibration method is effective
Ground-based tomographic radar imaging introduces a multitude of systematic biases due to the short range between antennas and the scene observed
Summary
Radar tomography is a remote sensing technique for acquiring a rendering of the threedimensional radar reflectivity of a scene. The reflectivity of natural scenes such as snow and forests exhibit temporal variations as the scenes are affected by changing weather conditions and seasons To study these phenomena in preparation for future SAR missions, ground-based radar tomography campaigns have been conducted to acquire tomographic observations of natural scenes over months to years, and at much smaller temporal intervals than what is possible with spaceborne SARs. Examples include SnowScat for snow observations [10], TropiScat for tropical forest observations [11] and BorealScat for boreal forest observations [12]. The instrument design has proven to be effective for studying scattering mechanisms and temporal variations of reflectivity at different heights within a scene [15] This instrument is implemented from off-the-shelf components and is proposed as an effective tool for future ground-based radar tomography studies. After a summary of the calibration procedure, limitations of the proposed calibration procedure are discussed
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