I. Introduction
The PROBLEM of emitter location attracts much interest in the signal processing, vehicular technology, and underwater acoustics literature. Defense-oriented location systems have been reported since World War I. Perhaps the first paper on the mathematics of emitter location, using angle of arrival (AOA), is due to Stansfield [1]. Many other publications followed, including a fine review paper by Torrieri [2]. The papers by Krim and Viberg [3] and Wax [4] are comprehensive review papers on antenna array processing for location by AOA. Recently, Van-Trees [5] published a book that is fully devoted to array processing. Positioning by time-of-arrival (TOA) is well known in radar systems [6], and in underwater acoustics [7]. In underwater acoustics, matched-field processing (MFP) is viewed as a promising procedure for source localization [8]. MFP can be interpreted as the maximum a posteriori (MAP) estimate of location given the observed signal at the output of an array of sensors [8], [9]. Another interpretation of MFP is the well-known beamforming extended to wide-bandwidth signals, nonplanar wave fields, and unknown environmental parameters.