REPEAT-PASS INTERFEROMETRY WITH AIRBORNE SYNTHETIC APERTURE RADAR

In this paper, we demonstrate for the first time that interference can be observed by coherently combining pairs of either X- or C-band airborne synthetic aperture radar (SAR) images from separate passes over the same test site. Coherence between separate images is obtained only if the aircraft is flown, and the data processed, such that each resolution cell in the two images is viewed with very nearly the same geometry. Successful repeat-pass interferometric results were obtained from those passes flown by the CCRS Convair 580 aircraft with flight-line offsets less than a few tens of meters. A summary of the experiment, the phase correction for nonrectilinear aircraft motion, and the subsequent data processing is provided. Repeat-pass interferometry with airborne SAR opens the possibility for temporal coherence studies and differential interferometric SAR experiments with the flexibility afforded by the airborne platform. This is demonstrated in the current work by showing a loss of coherence at both C- and X-band for forested areas under light to moderate winds, by measuring the height of a building, and by measuring the movement of a radar reflector to an accuracy on the order of one millimetre. The latter experiment reinforces the expectation that differential SAR interferometry, based on data from three or more passes, can detect and measure changes on the surface of the Earth to a fractional radar wavelength scale.