Bistatic range refers to the basic measurement of range made by a radar

Radar

Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

 or sonar

Sonar

Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...

 system with separated transmitter and receiver. The receiver measures the time difference of arrival of the signal from the transmitter directly, and via reflection from the target. This defines an ellipse of constant bistatic range, called an iso-range contour, on which the target lies, with foci centred on the transmitter and receiver. If the target is at range R_rx from the receiver and range R_tx from the transmitter, and the receiver and transmitter are a distance L apart, then the bistatic range is R_rx+R_tx-L. Motion of the target causes a rate of change of bistatic range, which results in bistatic Doppler shift

Bistatic Doppler shift

Bistatic Doppler shift is a specific example of the Doppler effect that is observed by a radar or sonar system with a separated transmitter and receiver. The Doppler shift is due to the component of motion of the object in the direction of the transmitter, plus the component of motion of the...

.

Iso-range contour

Generally speaking, constant bistatic range points draw an ellipsoid with the transmitter and receiver positions as the focal points. The iso-range contours are where the ground slices the ellipsoid. When the ground is flat, this intercept forms an ellipse. Note that except when the two platforms have equal altitude, these ellipses are not centered on the specular point.