Genetic algorithm inversion of the 1997 Geoacoustic Inversion Workshop test case data

An analysis of the 1997 Geoacoustic Inversion Workshop test case data was c arried out to benchmark the performance of a Genetic Algorithm (GA) inversi on code called SAGA_INV.(1) The inversion program made use of Westwood's OR CA propagation model,(2) FORTRAN subroutines, and Interactive Data Language (Research Systems Inc. IDL). SAGA_INV is capable of performing inversions with either Simulated Annealing (SA) or GA optimization schemes; however, o nly the GA portion of the code has been benchmarked with the workshop test cases at the present time. Not all of the workshop test cases were processe d: this study was concerned only with the GAL, SD, SO, AT, and WA data sets . The CAL data was processed using three different cost functions: (i) stan dard Bartlett processor, (ii) a broadband coherent processor, and (iii) a t ransmission loss mismatch function. These processors were applied to three frequency bands: (i) 76 frequencies between 25 Hz and 100 Hz, (ii) nine fre quencies between 28 Hz and 36 Hz, and (iii) 13 frequencies between 44 Hz an d 56 Hz. The latter two frequency regimes were intended to simulate 1/3-oct ave bands centered at 32 Hz and 50 Hz, respectively. Four different receivi ng arrays were simulated: (i) a 1550 m aperture horizontal, bottom mounted array at approximately I-km range, (ii) a similar array at approximately 4. 2-km range, (iii) a 55-m aperture la-dement vertical array located at l-km range, and (iv) a similar vertical array at 5-km range. In addition to proc essing the CAL data set, all three subcases of the SD, SO, AT, and WA data sets were also processed; however, only the transmission loss cost function and the two simulated 1/3-octave bands were considered for these test case s.