A general radar equation for the bistatic acoustic sounder

Abstract

A radar equation which can be applied to any bistatic acoustic sounder is derived. The equation reduces to the expression normally used for the special case of the monostatic sounder. Numerical results using this equation are given for specific acoustic sounders, including the relative contributions to the scattering from the temperature and velocity parameters (C: and C:), the effect of wind speed on the scattered intensity and the measurement of horizontal wind velocity.

Quantitative low-level acoustic sounding and comparison with direct measurements

“…Equation (5) does not take into account either excess attenuation, i.e., the loss of acoustic intensity that results from refraction by the wind (Neff, 1978;Moulsley and Cole, 1980) or turbulent beam broadening (Neff and Haugen, 1978;Clifford and Brown, 1980;Soom and Gu, 1981). Refraction produces a change in the angle of arrival of the backscattered sound given by (Neff, 1978), $(z) = 2 s 44 ds, CZ 0…”

“…This change results in a reduction of the received intensity caused by lower off-axis sensitivity of the antenna. The precise amount of refractive attenuation depends on the antenna beam pattern and the angular dependence of the scattering cross-section (Moulsley and Cole, 1980), as well as on the amount of turbulent beam broadening (Neff, 1978). Beam broadening by turbulence is less understood at the moment, and comparison of theoretical predictions with experimental results shows only order-ofmagnitude agreement (e.g., Haugen and Kaimal, 1978;Neff, 1978).…”

“…TO overcome these relative disadvantages of the usual acoustic sounders and to provide detailed, continuous observations of atmospheric boundary-layer structure, a new generation of high-frequency acoustic sounders has been developed (Moulsley and Cole, 1980). They operate at frequencies above 4000 Hz.…”

A quantitative comparison of horizontal and vertical acoustic sounding with in-situ measurements

“…The antenna radiation patterns for use in the radar equation were calculated from the array geometry (Moulsley et al, 1978;Moulsley and Cole, 1980).…”

“…The first two are functions of temperature, humidity and to a lesser extent pressure, and can be accurately calculated from measurements of these parameters (Sutherland, 1975) for any given frequency. Excess attenuation is the term used for loss of acoustic intensity due to refraction by the wind (Neff, 1978;Moulsley and Cole, 1980) and turbulent beam broadening (Brown and Clifford, 1976;Clifford and Brown, 1980). Refraction results in a change in the angle of arrival of the backscattered sound which gives rise to loss of received intensity due to the lower-sensitivity of the receiving antenna off-axis.…”