Preliminary results will be presented for TESPEX (Test of Environmental Signal Processing Experiment), which was performed in May 1993 off the east coast of New Zealand in a region of three‐dimensional bathymetry variations. This complex environment was exploited to minimize ambiguity in environmental source tracking with a single receiver [Collins et al., J. Acoust. Soc. Am. 90, 2366 (1991)]. To overcome limited knowledge of environmental parameters, the acoustic field was measured by a fixed array of receivers while a ship towing a source swept over a sector. The receivers were linked to a recently developed satellite telemetry buoy that transmitted time series to a centralized computer facility for real time analysis. Expensive ship time was traded off for cheap computation time by interpolating the acoustic field using a WKB representation that permits a sparse sampling in azimuth. The main computational task for the data basing involves solving a nonlinear optimization problem for the WKB amplitude a...