Rectilinear coordinate frames for Deep sea navigation

Since 1964 the National Deep Submergence Facility and Deep Submergence Laboratory at the Woods Hole Oceanographic Institution (WHOI) have performed thousands of scientific dives with human occupied, remotely operated, and towed vehicles. Each of these vehicles uses an equirectangular map projection within their navigation systems, colloquially known as the AlvinXY coordinate scheme. Equirectangular projections provide a simple, affine mapping between geographic coordinates and the coordinates of a cartesian grid. Additionally, AlvinXY and similar coordinate systems disregard the effect of depth upon the coordinate mapping. Advances in underwater navigational instrumentation during the past forty years now allow localization to such precision that, in some cases, the precision of the navigation solution is comparable to that of errors introduced by working in this simple coordinate space. In this paper, we characterize the effects of projection errors in this system upon vehicle navigation and localization for deep oceanographic vehicles today.