INTEGRATED SATELLITE INTERFEROMETRY - TROPOSPHERIC NOISE, GPS ESTIMATES AND IMPLICATIONS FOR INTERFEROMETRIC SYNTHETIC-APERTURE RADAR PRODUCTS

Interferometric synthetic aperture radar (INSAR), like other astronomi c and space geodetic techniques, is limited by the spatially and tempo rally variable delay of electromagnetic waves propagating through the neutral atmosphere. Statistical analysis of these variations, from a w ide variety of instruments, reveals a power law dependence on frequenc y that is characteristic of elementary (Kolmogorov) turbulence. A stat istical model for a major component of the delay fluctuations, the ''w et'' component, has previously been developed by Treuhaft and Lanyi [1 987] for very long baseline interferometry. A continuous Global Positi oning System (GPS) network is now in place in southern California that allows estimation of, along with geodetic parameters, the total delay due to the atmosphere above each site on a subhourly basis. These mea surements are shown to conform to the Treuhaft and Lanyi (TL) statisti cal model both temporally and spatially. The TL statistical model is a pplied to the problem of INSAR and used to produce the covariance betw een two points separated in time and/or space. The error, due to the a tmospheric variations, for SAR products such as topography and surface deformation is calculated via propagation of errors. There are two me thods commonly cited to reduce the effect of atmospheric distortion in products from SAR interferometry, stacking and calibration. Stacking involves averaging independent interferograms to reduce the noise. Cal ibration involves removing part (or all) of the delay using data from an independent source such as total zenith delay estimates from contin uous GPS networks. Despite the relatively poor spatial density of surf ace measurements, calibration can be used to reduce noise if the measu rements are sufficiently accurate. Reduction in tropospheric noise inc reases with increasing number of measurement points and increasing acc uracy up to a maximum of root N, where N is the number of points. Stac king and calibration are shown to be complementary and can be used sim ultaneously to reduce the noise to below that achievable by either met hod alone.