MFP Benchmark Inversions via the RIGS Method

Abstract

This paper discusses the geoacoustic inversion results obtained on the Workshop '97 benchmark data via the Refined Iterated Grid Search (RIGS) method. We find that the method can be highly accurate in estimating geoacoustic and source localization unknowns for the ten test scenarios attempted. The original method formulation using KRAKEN as the embedded propagation code produced the results presented at the workshop where we found that some parameters are extremely well determined, i.e. sediment attenuationα sed (within 1% in all 3 cases: ATa, ATb, ATc), sediment densityρ sed (within 5% in all ten subcases: SD, AT, SO, WAa), source ranger sou to within 40 m and source depthz sou to within 2 m (in all four subcases SO and WAa). Moreover, sediment sound-speed gradients γ were also well determined (within 8%) except for very thin sediments/subcase ATb where sediment thickness h sed ≈ 13 m). However, more recent, post-workshop results using ORCA embedded in the RIGS inversion software has resulted in even better results. Five of the original ten subcases have been re-done, and those results are also shown in this paper. In particular, we find that for the new results: r sou is now accurate to within 11 m, z sou to within 0.2 m, and all geoacoustic properties (except for half-space density ρ hsp ) are accurate to within 5%.