Radar studies of the earth

Radar backscatter from the ground was investigated in May, 1966, by aircraft and rocket flights over the Tularosa Basin area in New Mexico. An L-band radar with a peak power of 100 kW was flown to an altitude of 165 km, where echoes in orthogonal polarizations were monitored. The purpose of the experiment was to observe the behavior of the radar echo as a function of altitude and subsequently to relate the echo behavior to the measured electrical characteristics of the surface. Soil samples taken from the target area and measured in the laboratory had an average moisture content of 3.6 percent, dielectric constants between 2.8 and 4.8, and loss tangents between 0.001 and 0.2. The loss tangents computed from penetration measurements were somewhat higher (0.37). In most cases, the echo power amplitude appeared to vary as the inverse altitude squared for both the direct- and cross-polarized vertical incidence echo components. The average values for dielectric constant and loss tangent computed from the echo characteristics were ε = 3.4 and tan Δ = 0.25, which are in fair agreement with the soil sample measurements. An unexpected result was the observation of a specular cross-polarized echo component.