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Speaker：Dr. Björn Lund (University of Miami, Rosenstiel School of Marine and Atmospheric Science, Center for Southeastern Tropical Advanced Remote Sensing)

Title：Shipboard marine X-band radar applications in oceanography.

Time：12/27 (Thu) 14:20~15:10

Location：Room 232 of IONTU
 

Abstract：

Shipboard marine X-band radars (MRs) are commonly used for ship navigation purposes, where the radar return from the sea surface has long been considered noise. Over the past 30 years, however, MR has been used for studying a broad spectrum of physical phenomena with surface roughness signatures, including surface and internal gravity waves, oil spills, and sea ice. This presentation gives an overview of MR applications in oceanography, with a special focus on an advanced near-surface current and bathymetry mapping technique recently developed at University of Miami. This technique uses the long (>15 m) ocean wave signal within MR backscatter intensity image sequences to derive near-surface current and bathymetric maps at ~500 m resolution and up to a maximum range of ~4 km.

I will start this presentation with results from the Lagrangian Submesoscale Experiment (LASER) and Submesoscale Processes and Lagrangian Analysis on the Shelf (SPLASH) experiment in the Gulf of Mexico. LASER was conducted from Jan-Feb 2016 near the DeSoto Canyon, an area characterized by strong submesoscale currents. SPLASH took place within the shallow waters of the Mississippi River delta from April-May 2017. Both experiments aimed to measure submesoscale upper ocean currents and their potential impact on oil spills. The shipboard MR current maps acquired during LASER were validated using 100s of biodegradable GPS-tracked CARTHE drifters. For a total of 4,240 MR–drifter pairs, the root-mean-square error for the current speed is 4 cm s−1 and for the current direction is 12°. The MR samples currents at a greater effective depth than the CARTHE drifters (1-5 m vs. ~0.4 m). The mean MR–drifter differences are consistent with a wave- and wind-driven vertical current profile that weakens with increasing depth and rotates clockwise from the wind direction (by 0.7% of the wind speed and 15°). This presentation furthermore provides first current and bathymetry results from the SPLASH data set. Finally, I will present sea ice drift maps derived from shipboard MR data acquired during the 2015 Arctic Sea State experiment in the Chukchi and Beaufort seas. My work suggests that sea ice drift and wind speed near the ice edge were only weakly correlated (r2=0.34), which is contrary to conventional wisdom.

These techniques have great potential in observational oceanography, as they allow research vessels to map the horizontal upper ocean current structure, complementing the vertical profiles measured by ADCP, yield the bathymetry of areas that are otherwise difficult to survey, and help explain sea ice dynamics in a changing Arctic.