Centimeter-Level Positioning of Seafloor Acoustic Transponders from a Deeply-Towed Interrogator

摘要

An array of three seafloor transponders was acoustically surveyed to centimeter pieci-sion with a deeply-towed interrogator. Measurements of two-way acoustic travel lime and hydrostatic pressure made as the interrogator was towed above the array were combined in a least-squares adjustment to estimate the interrogator and transponder positions in two surveys spanning two years. No transponder displacements were ex-pected at this site in the interior of the Juan de Fuca Plate (48°11′ N, 127°12? W) due to the lack of active faults. This was confirmed to a precision of ±2 cm by least-squares adjustment. Marginally detectable blunders in the observations were shown 10 affect the transponder position estimates by no more than 3 mm, demonstrating the geometric strength of the data set. The accumulation of many hundreds of observations resulted in a significant computational burden on the least-squares inversion procedure. The sparseness of the normal matrix was exploited to reduce by a factor of 1000 the num-ber of calculations. The acoustic survey results suggested that the near-bottom sound speed fields during the two surveys were in better agreement than inferred from yearly single-profile conductivity, temperature, and pressure (CTD) measurements.