Space SAR interferometers for detailed terrain assessment with simultaneous generation of paired signals

Abstract

Operational or long-term interferometric shooting using SAR (synthesized antenna aperture radar) enables to obtain detailed DTM (digital terrain models) and yet currently vastly used methods for multi-pass interferometry with a single space vehicle or single-pass interferometry with multiple space vehicles are subject to temporal decorrelation of interferometers’ paired signals, which drastically reduces their efficiency. Thus it is advisable to ensure simultaneous generation of interferometer paired signals. The best investigated and promising method of terrain evaluation is the bistatic one, which enables simultaneous reception of reflected signal by two spaced-apart independent antennas. Another way to construct a simultaneous SAR interferometer is performed via multisession shooting using a single space vehicle with SAR in squint survey. The paper is aimed at comparative analysis of two methods for constructing space SAR interferometers with simultaneous generation of paired signals that have maximum efficient response and noise immunity. To solve the problem there were thorughly reviewed bistatic and squint single-pass survey modes; there were obtained relations to calculate the mean square error for measuring relative terrain height and there was performed improvement for selecting interferometer base in regard to enhance measurement accuracy. An example for calculation of 500 km orbit altitude of space vehicle and SAR operating in X-band with spatial resolution of 2...4 m is considered. Optimal values were defined for the base: they are in the range of 1.5...3 km for lateral bistatic interferometer, and they are in the range of 13...20 km in case of single-pass interferometer in squint survey mode. Calculation results have also demonstrated that potential terrain evaluation accuracy depends on viewing angle and may be up to 1...2 m when using two SAR in bistatic mode and up to 3...8 m when using one SAR in squint mode. The analysis made it clear that squint single-pass survey mode comes short of DTM measurement accuracy compared to bistatic survey mode. Implementation simplicity, low-level requirements for navigational support, possibility to resume repeatitive measurements during the same pass are among advantages of single-pass SAR interferometer in squint survey.