A Bistatic Multiple-Doppler Radar Network

Abstract

A multiple-Doppler radar network can be constructed using only one, traditional, transmitting pencil-beam radar and one or more passive, low-gain, nontransmitting receivers at remote sites. Radiation scattered from the pencil beam of the transmitting radar as it penetrates weather targets can be detected at the receive-only sites as well as at the active transmitter. The Doppler shifts of the radiation received at all the sites can be used to construct two- and three-dimensional wind fields in a manner similar to that used with traditional Doppler radar networks. There are unique scientific advantages to a bistatic multiple-Doppler network: 1) all radial velocity measurements from individual resolution volumes are collected simultaneously since there is only one source of radiation; 2) the intensity of the obliquely scattered radiation can be compared to Rayleigh scattering predictions and used for hail detection; 3) rapid scanning of localized weather phenomena can be aided by elimination of the need to scan with multiple radars. This type of multiple-Doppler radar network also has significant economic advantages. Passive sites contain no high-voltage transmitting equipment or large rotating antennas. They require no operators and much less maintenance. We estimate initial investment costs, and subsequent operational and maintenance costs are less than one-thirtieth that of conventional radars. There are shortcomings particular to these types of networks: 1) passive, low-gain, receiving sites are more sensitive to contamination from transmitter sidelobes and to secondary scattering from weather echoes; 2) low-gain receiving sites are less sensitive to weak weather echoes; 3) Cartesian (u, v, w) wind fields derived from bistatic network data exhibit about twice the expected error as those constructed from data from traditional monostatic networks containing equal numbers of radars. Multiple scattering and sidelobe contamination levels are acceptable in most situations and can be reduced with the use of higher-gain receiving antennas. The low sensitivity and higher errors of the bistatic networks can be ameliorated with the use of multiple passive sites, a practical solution due to their very low cost.