Measuring seafloor motion in shallow coastal water is challenging due to strong and highly variable oceanographic effects. Such measurements are potentially useful for monitoring near-shore coastal subsidence, subsidence due to petroleum withdrawal, strain accumulation/release processes in subduction zones and submerged volcanoes, and certain freshwater applications, such as volcano deformation in caldera-hosted lakes. We have developed a seafloor geodesy system for this environment based on an anchored spar buoy topped by high-precision GPS. Orientation of the buoy is measured using a digital compass that provides heading, pitch, and roll information. The combined orientation and GPS tracking data are used to recover the three-dimensional position of the seafloor marker (anchor). A test system has been deployed in Tampa Bay, Florida, for over 1 year and has weathered several major storms without incident. Even in the presence of strong tidal currents which can deflect the top of the buoy several meters from vertical, daily repeatability in the corrected three-component position estimates for the anchor is 1-2 cm or better.Plain Language Summary To measure seafloor motion in shallow water, we built a spar buoy and put a GPS antenna and a digital compass (three-dimensional orientation sensor) on top of it. The buoy rests on the sea bottom using a heavy concrete ballast. Rotation and other movements of the buoy are measured by the digital compass and GPS. Position of the ballast can be calculated based on these measurements. We tested the system in Tampa Bay, Florida, and found that it is able to measure motion of the anchor with an uncertainty of 1-2 cm or smaller.

Satellite-derived daily sea surface temperature (SST) products are compared with moored SST observations on the West Florida Shelf during the time period of Hurricane Irma. Most of the SST products compare reasonably well with the moored data at the location of 25-m depth, where SST dropped by about 1°C after the hurricane passage. However, most of the SST products did not show the rapid SST drop at the location of 50-m depth where the surface water was cooled by about 4°C within 1 day in response to the hurricane passage. This finding has important implications to air-sea interaction studies and hurricane simulations, in which SST data play an important role. The limitations of the popular satellite products call for additional coastal ocean observations as well as proper inclusion of the real-time observations in satellite-derived products.

No abstract