Determination of vegetation height from SAR interferometry: a theoretical study

In this paper the theoretical aspects of estimating vegetation parameters from SAR interferometry is presented. In conventional applications of interferometric SAR (INSAR), the phase of the interferogram is used to retrieve the location of the scattering phase center of the target. Although the location of scattering phase center for point targets can be determined very accurately, for a distributed target such as a forest canopy this is not the case. For distributed targets the phase of the interferogram is a random variable which in general is a function of the system and target attributes. To relate the statistics of the interferogram phase to the target attributes, first an equivalence relationship between the two-antenna interferometer system and an equivalent Δk radar system is established. This equivalence relationship is needed to related the frequency correlation function of distributed targets, which can conveniently be obtained experimentally, analytically, or numerically, to the phase statistics of the interferogram. It is shown that the frequency correlation function of distributed targets which in turn is a function of scattering mechanisms and system parameters determines the accuracy with which canopy height can be estimated. It is also shown that for a uniform closed canopy the extinction and the physical height of the canopy top can be estimated very accurately. Some analytical and numerical simulations are demonstrated