Ocean Surface Drifting Buoy System Based on UAV-Enabled Wireless Powered Relay Network

We design an ocean surface drifting buoy system based on an unmanned aerial vehicle (UAV)-enabled wireless powered relay network in which the UAV acts as mobile hybrid access point that broadcasts energy to all buoys in the downlink and forwards information from the buoys to a ship signal tower (ST) in the uplink. In order to maximize the resource allocation efficiency of the system, due to the different initial energy reserve of the buoys, a novel communication mode selection strategy is proposed. In the direct transmission mode (DT mode), an energy-sufficient buoy transmits information directly to the ST, and in the relay transmission mode (RT mode), an energy-insufficient buoy relays information to the ST through the UAV. By applying the block coordinate descent and successive convex optimization, a joint UAV trajectory and resource allocation algorithm is proposed to maximize the minimum throughput of the buoys to work in the RT mode. Simulation results show that the proposed algorithm can significantly improve the minimum throughput of the ocean surface drifting buoys.

Sea Surface Temperature Retrieval from the First Korean Geostationary Satellite COMS Data: Validation and Error Assessment

Korea’s first geostationary satellite, the “Communication, Ocean, and Meteorological Satellite” (COMS), has been operating since 2010. The Meteorological Imager (MI), an sensor on-board the COMS, has observed sea-surface radiances for the estimation of sea surface temperature (SST) in the western Pacific Ocean and eastern Indian Ocean. To derive the SST coefficients of COMS, quality-controlled surface drifting buoy data were collected for the period of April 2011 to March 2015. A collocation procedure between COMS/MI data and the surface drifter data produced a matchup database for 4 years from 2011 to 2015. The coefficients for the COMS/MI SST were derived by applying appropriate algorithms, i.e., the Multi-channel SST (MCSST) and Non-linear SST (NLSST) algorithms, for daytime and nighttime data using a regression method. Validation results suggest the possibility of the continuous use of the coefficients as representative SST coefficients of COMS. The estimated SSTs near the edge of a full disk with high satellite zenith angles over 60° revealed relatively large errors compared to drifter temperatures. Most of NLSST formulations exhibited overestimation of SSTs at low SSTs (<10 °C). This study suggests an approach by which SST can be measured accurately in order to contribute to tracking climate change.

An Experimental Study on the Current-Following Characteristics of a Surface Drifting Buoy

The water-following capabilities of surface drifting buoy are investigated through analyzing the hydrodynamic factors which influence the buoy’s floating, so as to improve the precision of ocean currents measured by drifters, and optimize the design of drifters. The force balance equation of surface drifting buoy is established, and the wind coefficient of drifter model is obtained and analyzed. A prototype based on GPS (Global Positioning System) and BeiDou-1 (BeiDou Satellite Navigation Experimental System) is designed to collect surface currents near Gulf of Jiaozhou. Calculated results indicate that the velocity data, which take the wind coefficient into account, are more approaching the measuring value of fixed current-meter. That provides some experimental validities to the modelling and designing of surface drifting buoy. This study also shows that the surface trajectory from GPS and BeiDou-1 float provides a new means to measure surface circulations in the global ocean at real time, and that the estimated currents could be one of the important sources to improve our understanding for ocean dynamics characteristics.

Estimating Surface Divergence of Ocean Eddies Using Observed Trajectories from a Surface Drifting Buoy

A method is described that estimates the time evolution of surface divergence and other secondary circulation properties of an ocean eddy. The method is novel because it is applied to the observations of a single surface drifting buoy. Surface drifting buoys located on ocean eddies provide Lagrangian trajectories that orbit the local extremum in geopotential. At each instance, the position of the buoy lies on the boundary of a closed material surface over the eddy. Assuming, on an ocean eddy, that the material boundary points vary smoothly in time, a method is developed to estimate all points along this boundary. An ellipse is fitted to the approximated material boundary to provide a continuum of properties, including centroid, aspect ratio, orientation, and area. The time rate of change of these properties provides approximations to the eddy velocity, moment of inertia, secondary rotation, and surface divergence. Two surface drifting buoys deployed on an anticyclonic eddy in the East Australian Current are used to demonstrate the analysis method. The estimated surface divergence is compared and interpreted using the observed separation of the two drifting buoys and other independent observations.

Fall–Winter Current Reversals on the Texas–Louisiana Continental Shelf

Fall–winter recurrence of current reversal from westward to eastward is identified on the Texas–Louisiana continental shelf using the current-meter [Texas–Louisiana Shelf Physical Oceanography Program (LATEX-A)] and near-surface drifting buoy [Surface Current and Lagrangian Drift Program (SCULP-1)] observations in 1993 and 1994. Reversal events roughly satisfy the Poisson distribution with one current reversal nearly every 12 days. Synoptic winds seem responsible for the current reversal events. Other processes such as offshore eddies shed from the Loop Current and river runoff are less important to change alongshore flow direction at synoptic scales. A statistical model is established to predict the synoptic current reversal using the surface wind observations.