Coastal marine X-band radar bathymetry and current mapping

Abstract

This presentation studies coastal marine X-band radar (MR) bathymetry and current measurements made in Monterey Bay, California, during the Coastal Land–Air–Sea Interaction (CLASI) experiment from Jul-Aug 2021. Numerous past studies have shown coastal MR bathymetry and, to a lesser extent, current measurements, but only a few of them have investigated their environmental limitations. Widely cited thresholds for MR ocean measurements are a minimum wind speed of 3 m/s and significant wave height of 0.5 m. Monterey Bay has a strong year-long diurnal sea breeze which also influences the wave height. As a result, wind and wave conditions fluctuated from favorable to unfavorable for MR ocean measurements on a quasi-daily basis. Here, we examine the limitations of MR bathymetry and current measurements as a function of wind and wave conditions, which were measured by an Air–Sea Interaction Spar (ASIS) buoy within the radar field of view. Unlike the popular cBathy algorithm, which adjusts its bathymetry results to the mean water level using ancillary tide gauge measurements and applies a Kalman filter that ingests several days of data per bathymetry estimate, we measure the bathymetry with a temporal resolution of 4 min albeit at a relatively low spatial resolution of 360 m. This allows MR-based measurements of tidal elevation, which we validate using data from the CO-OPS tide gauge in Monterey. The MR current measurements are validated using an ADCP that was mounted on the ASIS buoy. The novelty of this study lies in the comprehensive evaluation of the MR bathymetry and current measurements' environmental limitations. We show how their maximum range decreases for wind speeds under 4 m/s with a success rate of <20% for winds <2 m/s and <10% for winds <1 m/s. These findings can guide investigators who plan to include MR ocean measurements in their coastal field studies.