Range limitations on acoustic adjoint inversions

Measurement of range dependent ocean sound speed is an important to many ocean acoustic problems, including source localization and tomography. The recent prevalence of low cost robotic platforms such as oceanographic gliders has increased the availability of long-term measurements of the ocean environment, but in many cases their usefulness is limited by the spatial-temporal resolution of their measurements. Combining them with additional acoustic inversion sampling of the same sound speed field may increase these measurements´ resolution. This paper investigates a method of combining the adjoint method, a local acoustic inversion, with glider measurements to create reliable sound speed measurements at high sampling rates. The performance of this method is found to be highly sensitive to the total range study area with a simulation study comparing root mean squared error over 30 simulated inversions. This limitation may be an effect of the limited ensonification of the water column at longer ranges, which is shown using a ray trace model.