TABLE OF CONTENTS Despite attempts to account for the relevant parameters in empirical models (for example, [583, 669, 670, 346]), calculated predictions of clutter power can deviate significantly from measurements and among various models. A significant source of variability may be traced to the atmospheric conditions that affect low-altitude radar propagation. The present discussion considers two models: one has been developed at the Georgia Institute of Technology [346] ("GIT" model); a second draws from the reflectivity data tabulated in this chapter, data from Barton [43], as well as features of the GIT model ["HYB" (hybrid) model]. A mathematical description of the GIT model is given at the end of this section; the HYB model is described in Ref. [583].
Differences among various models are most apparent at grazing angles ? below a few degrees. At small angles, reflectivity in the GIT model varies approximately as ?; the relationship is closer to ? 2 in the HYB model, as well as that of Sittrop [669, 670]. A small grazing angle dependence of ? 4 is predicted from theoretical interference effects, a discussion of which may be found in references [583, 444, 532]. Some measurements conforming to a ? 4 law have been reported [392]. On the other hand, a ? 2 dependence is evident in various empirical models, including the HYB model. One hypothesis is that the measured data used to adjust empirical parameters in the GIT model were collected during...
