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New Way to Measure Seafloor Motion with GPS in Shallow Seas

Researchers: Surui Xie, Timothy H. Dixon, Rocco Malservisi, Mel Rodgers, Jason Law, Randy Russell, Chad Lembke, David F. Naar, Jennifer Brizzolara, John W. Gray, Matt Hommeyer, and Jing Chen, University of South Florida; Giovanni Iannaccone and Sergio Guardato, Istituto Nazionale di Geofisica e Vulcanologia; and Daniele Calore and Nicola Fraticelli, Hydra Solutions.

Written by Linda Rowan
8 April 2020


A new way to measure seafloor motions with Global Positioning System (GPS) in shallow seas is tested in Tampa Bay, Florida. The system uses a GPS receiver, 3-axis compass, spar and weighted anchor. Observations over many months on the bayside of Egmont Key in Tampa Bay Florida indicate seafloor motions in three dimensions can be measured with an accuracy of 1 to 2 centimeters. The method can be applied for offshore oil operations, lakes around volcanic edifices, shallow submarine regions near the coasts that are above active subduction zones and for other applications.


GPS is utilized on land to measure ground motions, for surveying, for navigation and other purposes around the world. Many researchers are working to develop a GPS system that can measure seafloor motions in water and effective techniques have been developed for deep water, in particular. Here the authors test a new technique to measure seafloor motions in shallow water. The tests are conducted on the bayside of Egmont Key in Tampa Bay Florida where tides, weather, and the shipping channel can affect the measurements. The seafloor consists of limestone with some sediment, rock rubble, shells and human garbage and the depth to the seafloor at the site is 23 meters below the water surface.

The GPS system is based on the Multiparametric Elastic‐Beacon‐Based Devices and Underwater Sensor Acquisition (MEDUSA) research and monitoring marine infrastructure used by INGV to monitor vertical deformation of the seafloor in the Gulf of Pozzuoli in southern Italy, adjacent to the Campi Flegrei volcanic area. Here the authors measure heading, pitch and roll and perform a three‐dimensional transformation to recover the horizontal and vertical components of the seafloor motion.


The modified GPS system was sensitive to tides, weather and some scouring around the seafloor anchor. Nonetheless with careful consideration of these affects and other factors that contribute artifacts, the method can measure seafloor motions in three dimensions with an accuracy of about 1 to 2 centimeters. Over time, the system can be fine tuned to remove more of the noise and potentially improve the precise positioning. The technique is useful for monitoring shallow water energy extraction industries, underwater volcanic systems, and near coastal subduction zone processes. Deployment of such systems could enhance management of natural resources and mitigation of natural hazards.

Related Links


Xie, S., Law, J., Russell, R., Dixon, T. H., Lembke, C., Malservisi, R., et al (2019). Seafloor geodesy in shallow water with GPS on an anchored spar buoy. Journal of Geophysical Research: Solid Earth, 124, 10.1029/2019JB018242.


seafloor geodesy, GPS

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Last modified: 2020-04-08  23:51:25  America/Denver