Thomas F. Haddock

Millimeter-wave bistatic scattering from ground and vegetation targets

A 35-GHz bistatic radar system was used to measure the attenuation through trees and the bistatic scattering pattern of tree foilage. The data were found to be in good agreement with a first-order multiple scattering model. Measurements were also made to study the angular vibration of the bistatic scattering coefficient of a smooth sand surface, a rough sand surface, and a gravel surface. The measurements, which were made for HH, HV (horizontal transmit, verticle receive), and VV polarization configurations over a wide range of the azimuth angle and the scattering angle, provide a quantitative reference for the design and use of millimeter-wave bistatic radar systems. >

Fluctuation statistics of millimeter-wave scattering from distributed targets

The applicability of the Rayleigh fading model for characterizing radar scattering from terrain is examined at 35 GHz for both backscattering and bistatic scattering. The model is found to be in excellent agreement with experimental observations for single-frequency observations of uniform targets such as asphalt and snow-covered ground. The use of frequency averaging to reduce signal fading variations was examined experimentally by sweeping the radar signal from 34-36 GHz in 401 steps. The results show that the formulation based on the Rayleigh model relating the reduction in signal fluctuation to the bandwidth used provides a reasonable estimate for the improvement provided by frequency averaging. >

Millimeter-wave radar scattering from snow 1. Radiative transfer model

Millimeter-wave (MMW) remote sensing of ground snow has attracted considerable interest in recent years. Because the size of the snow ice particle is comparable to the wavelength in the millimeter-wave region, we can no longer use a simple Rayleigh phase function or the small particle approximation usually used at microwave frequencies for calculating the extinction coefficient. In this paper we present a model for MMW scattering from snow using the vector radiative transfer theory and a Mie phase function. Assuming snow to consist of randomly distributed spherical particles embedded in a mixture of air and water, the vector radiative transfer theory is solved using the discrete ordinate method. The values of the extinction coefficient used in the calculations are based on a combination of experimental data and calculations using the quasi-crystalline approximation. The backscattering coefficient is calculated for different liquid water contents at 35, 95, and 140 GHz. We show that the backscattering coefficient is sensitive to liquid water content at all three frequencies, with 35 GHz being the most sensitive. Except for normal incidence, the effect of snow surface roughness is negligibly small for dry snow, and it is somewhat significant for wet snow at 35 GHz, but not at the higher frequencies.

Millimeter‐wave radar scattering from snow: 2. Comparison of theory with experimental observations

Using a truck-mounted platform, backscatter measurements were made at 35, 95, and 140 GHz for a variety of snow conditions to evaluate the radar response to incidence angle, surface roughness, and liquid water content. Good agreement was obtained between the experimental observations and theoretical calculations based on the numerical solution of the radiative transfer equation presented in the preceding paper. A notable exception is when the snowpack is in the refreezing phase of the diurnal cycle, during which the snowpack is characterized by a dry surface boundary with wet layers underneath. To accommodate this type of condition, a hybrid first-order numerical solution is proposed. The hybrid approach provides excellent agreement between theory and experiment.

A millimeterwave network analyzer based scatterometer

The Millimeterwave Polarimeter (MMP) is a network-analyzer-based scatterometer and reflectometer system that has been developed to characterize radar clutter at 35, 94, and 140 GHz. A Hewlett-Packard 8510A network analyzer is used in the MMP system as a signal conditioner and processor to facilitate real-time data reduction, to reduce the short time-delay leakage noise inherent in traditional FM/CW radar, and to further enhance the signal-to-noise ratio of the system through signal processing techniques. Operation of the system at millimeter wavelengths is achieved with upconversion and harmonic downconversion. The use of harmonic downconverters permits low-frequency signal connections between components of the system and allows easy reconfiguration in either scatterometer, bistatic, or reflection/transmission modes. >

140-GHz Scatterometir System And Measurements Of Terrain

The goal of the University of Michigan millimeter-wave radar program is to characterize terrain scattering at 35, 94, and 140 GHz. The 140-GHz channel of a truck-mounted scatterometer system has recently been added to give the full desired operating capability. Two injection-locked 45.33-GHz Gunn oscillators use triplers to supply the up. and down-converters. Full polarization capability is obtained through the use of rotatable quarter-wave plates. Real-time signal processing and data eduction takes place in an HP 8510A automatic network analyzer on the truck-mounted platform. Sample measurements of millimeter-wave radar backscattering from vegetation and snow are given.