The Applicability of Ocean Physics Models to GNSS‐Acoustic Seafloor Geodesy

Abstract Global Navigation Satellite System‐Acoustic (GNSS‐A) seafloor geodetic observation is an effective technique not only for measuring offshore crustal deformation but also for detecting underwater sound speed structures. Collecting acoustic range data along survey tracks with broad spatial coverage is typically essential to detect horizontal gradients of the sound speed structure. Although acoustic ranging data sets with broad spatial coverage have been acquired using research vessels, the acquisition of such data sets has often been difficult using an unmanned sea surface platform, such as a Wave Glider. To ensure positioning accuracy for insufficient acoustic ranging data sets, constraining the horizontal gradients of the sound speed structure using independent information is essential. In this study, we examined the applicability of ocean models to improve GNSS‐A positioning accuracy for insufficient acoustic ranging data sets. We calculated the sound speed parameters expressing the horizontal gradients of the sound speed structure using the ocean models JCOPE2M and MOVE/MRI.COM, and compared them with those estimated by GNSS‐A using actual acoustic ranging data sets with broad spatial coverage. The results illustrated that these ocean models have the potential to improve the positioning accuracy when large‐scale horizontal inhomogeneity exists in the sound speed structure (e.g., an oceanic current). However, the GNSS‐A analysis results using actual data indicate a significant influence of small‐scale horizontal inhomogeneities, suggesting that higher‐resolution ocean models are required to further improve positioning accuracy.