1. A method for selecting a threshold for an adaptive coherence estimate detector for an airborne radar application and detecting a target signal using the threshold wherein a specific form of a target signal to be detected is known, said method comprising the steps of: determining a Doppler frequency for a clutter ridge of a clutter return from ground of a radar beam transmitted from an airborne radar antenna; determining the proximity of a Doppler band of interest to the Doppler frequency of clutter ridge; and setting the threshold of the adaptive coherence estimate detector based on the proximity of the Doppler band of interest to the clutter ridge.