Phase ambiguity determination for the positioning of interferometric sar data

Interferometric SAR (InSAR) has established itself as a useful technique for precise cloud-independent topographic surveying and for the monitoring of topographic change at sub-centimetric accuracies. Despite this, measurements of the phase are still only available modulo 2 π and this leads to an ambiguity problem that is usually not explicitly resolved.
This paper presents a generalised method for the precise determination of the phase ambiguity that is independent of datum and projection biases. The method is based on those applied to Global Navigation Satellite Systems (GNSS) signals and shows that the far-field approximation is insufficient for precise positioning. Geometric similarities between InSAR and radargrammetry are highlighted. The solution presented allows the geolocation of a target to an accuracy limited only by the accuracy of the transmit–receive time of the sensor.