Models of Land Clutter vs Grazing Angle, Spatial Distribution and Temporal Distribution - L-Band VV Polarisation Perspective

摘要

Land clutter issues and modeling from a perspective of L-band VV polarization are addressed. In particular, clutter distributions in three different dimensions are discussed in detail. First, a three-term model for the dependence of land clutter on grazing angle is proposed. The model is site- specific and landcover-dependent. Parameters for dominant types of landcover in the Northern Territory region are regressed using AirSAR and MCARM measurements as well as others available in the literature. Clutter spatial distribution also is investigated. Aimed at real-time implementation, a simple and fast parameter estimation scheme for the Weibull and K-distributions is provided. The estimates are found to be nearly identical to the maximum likelihood estimates. The final topic of discussion in the report is the clutter temporal distribution, or Doppler spectrum, which is due to the motion of moving parts of scatterers. The Doppler frequency of L-band land-clutter is low and decays rapidly, so there are no proper measured data to investigate. The discussion has been mainly based on material from the open literature. An exponential decay model and its associated parameters for various landcover, wind condition, and radar frequency, proposed by Billingsley (2002), is summarized. The main points of the model are that Doppler velocity decays exponentially; the shape parameter of the decay function is dependent on wind conditions and largely independent of radar frequency; and the ratio of dc component to ac component of the Doppler spectrum depends on wind conditions, type of landcover, and radar frequency, but is independent of polarization. Appendix A focuses on Surface Clutter at Low Grazing Angle Measured by Airborne Radar, and Appendix B examines Backscattering Coefficient of a Flat Conducting Surface of Infinite Extent at Normal Incidence. (10 tables, 45 figures, 28 refs.).