Marine X-Band Radar Currents and Bathymetry: An Argument for a Wave Number-Dependent Retrieval Method

B. Lund, B. K. Haus, H. C. Graber, J. Horstmann, R. Carrasco, G. Novelli, C. M. Guigand, S. Mehta, N. J.M. Laxague, T. M. Özgökmen

Research output: Contribution to journalArticle

Abstract

This study evaluates shipboard marine X-band radar (MR) near-surface current and bathymetry measurements under shallow water conditions. The retrieval algorithm is based on the surface wave signal within three-dimensional wave number frequency MR backscatter intensity variance spectra. The MR data were collected during a research cruise that investigated submesoscale processes and their impact on oil spill transport in the Louisiana Bight. The MR currents and bathymetry are validated using measurements from 500 GPS-equipped surface drifters, a shipboard acoustic Doppler current profiler, and a shipboard single-beam echo sounder. Earlier results from the same experiment but using a different set of sensors indicate strong upper ocean vertical current shear over a 3.5 hr period, despite only mild wind forcing. Here, the MR currents are derived as a function of wave number, providing a measure of vertical shear for the full duration of the cruise. Strong vertical shear is frequently observed, with a maximum difference of 0.42 m/s between the MR high (effective depth of ~0.9 m) and low (~2.4 m) wave number bins. Treating the drifter and echo sounder measurements as truth, the accuracies of the MR near-surface currents and bathymetry are 0.04–0.07 m/s and 1.2 m (or 7% of the mean water depth). However, it is shown that ~50% of the MR high wave number and drifter current differences is due to vertical shear. The shallow water MR near-surface current accuracy thus matches findings from a previous deep water validation where vertical shear was much weaker.

Original languageEnglish (US)
Article numbere2019JC015618
JournalJournal of Geophysical Research: Oceans
Volume125
Issue number2
DOIs
StatePublished - Feb 1 2020

Keywords

  • bathymetry retrieval
  • current retrieval
  • shipboard marine X-band radar
  • surface gravity waves
  • upper-ocean vertical current shear
  • validation

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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