A Study of Bistatic GNSS Radar

A Study of Bistatic GNSS Radar

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B J Coutts
Amanda Norton
University of Colorado, Boulder, CO, USA.

B J Coutts
Tore Lindgren
Luleå University of Technology, Luleå, Sweden.

B J Coutts
Dennis Akos
University of Colorado, Boulder, CO, USA.

Abstract
One of the more recent areas of GNSS research of increasing popularity is the study of reflected GNSS signals. This will enable the use of GNSS as a passive radar system that can be used as an alternative to radar altimetry and for ground feature characterization. Of interest is also the possibility to use GNSS signals for object detection. The advantage of using GNSS signals as a passive radar system is that it has complete earth coverage. The signals are, however, weak and the computational load associated with the analysis is heavy.

Monostatic and Bistatic Radar
In a conventional, monostatic radar system the transmitter and receiver is located on the same place. This performs a search by broadcasting a signal and receiving an echo at some later time. Subsequent analysis gives information about the reflecting object’s range, cross-section, and velocity. In contrast to this, a bistatic radar uses geographically separated transmitters and receivers. In GNSS bistatic radar, the GNSS satellite serve as the transmitter and the receiver is located on a fixed tower, airborne platform, or another satellite. Unlike the monostatic radar, where the signal is reflected back to the radar along the same path there are several possible routes of propagation in the bistatic case. This is illustrated in Fig. 1, where the direct signal and shortest path (specular) reflection is shown. Information about the direct signal is used to aid the detection of the reflected, often very weak, signals. The path delay of the specular reflection with respect to the direct signal is used together with the elevation and azimuth of the satellite to acquire information about the height above ground level (AGL) of the measurement platform [1].


Fig. 1. The bistatic GNSS radar concept [1].