The concept of bistatic radar is as old as the concept of radar itself [for a review of the history of bistatic radar see Glaser (1986)]. It consists of a system capable of sending a pulse (transmitter) at a given site and a system capable of receiving an echo from a target at a different site (receiver). The more conventional monostatic radar delivers the pulse and receives the echo at the same site and with the same antenna.

Several researchers have explored the use of bistatic radar systems for detecting weather echoes, among them Atlas et al. (1968), Doviak and Weil (1972), Crane (1974), Awaka and Oguchi (1982), and Dibbern (1987). In addition, some work has been done regarding the use of polarimetric parameters in a bistatic system by Shupyatsky (1974) and Aydin et al. (1998). But it was really after the pioneering work of Wurman et al. (1993) that the idea of bistatic radars in meteorology was reborn, especially due to its Doppler capability.

A bistatic multiple-Doppler network consists of one traditional transmitting Doppler radar and one or more passive, nontransmitting, nonscanning radar receivers at remote sites. Multiple bistatic receivers provide multiple-look angles at a volume of weather in the same manner as multiple Doppler radars do. The Doppler shifts of the radiation scattered obliquely by the raindrops toward the passive remote receiver can be measured. Then, with two or more Doppler measurements from different viewpoints, several techniques can be used for determining the full wind field over a particular area (Wurman et al. 1993; Protat and Zawadzki 1999).

The McGill University Bistatic Network has been implemented in collaboration with the University of Oklahoma and the National Center for Atmospheric Research. It became operational by the end of 1995 and has been operating almost continuously since then with a satisfactory stability. It consists of the McGill S-band scanning Doppler radar located 30 km west of downtown Montreal, and two bistatic receivers located south and northwest of the Island of Montreal (see configuration in Fig. 1 ).

A bistatic radar system uses a single source of illumination; thus, observations of individual storm regions by the transmitter and the bistatic receivers are taken simultaneously. This is not the case of the monostatic multi-Doppler radar system, unless a synchronized scanning is used. Radial velocities are not measured simultaneously but are separated in time up to the few minutes required for each radar to scan a given volume. In convective environments, significant storm feature evolution can occur between these measurements.

There are some disadvantages in the bistatic radar approach as compared to the multiple-Doppler measurements. The use of low-gain receiving antenna can cause the receiving sites to be less sensitive (near 15 dB less) than the traditional high-gain radars at comparable range. In addition, the wide viewing angle of the antenna can cause the bistatic receivers to be more sensitive to multiple scattering contamination and sidelobe contamination. The success of the prototype system (Wurman 1994) suggested that the above limitations are often not serious. However, operational experience with the bistatic network at McGill University suggested sidelobe contamination (SICO) should be given serious consideration.