An Improved Quality Flag for QuikSCAT coastal winds

Version 4.0 of the Jet Propulsion Laboratory QuikSCAT L2B wind vector product was publicly released on April 5, 2018 from the Physical Oceanography Data Active Archive Center (PO.DAAC). The data include the entire period of nominal operations (1999-2009) for QuikSCAT. Coastal winds are retrieved using the Land Contamination Ratio with Expected Sigma0 (LCRES) technique which retrieves winds significantly closer to the coast than has been done before. Figure 1 below depicts the counts as a function of distance from coast for the newest version and two earlier versions. Version 3.0 and earlier versions made use of a conservative land mask so that winds closer to the coast than 20-km were seldom retrieved. In version 3.1, the Land Contamination Ratio (LCR) technique was applied. LCR precisely measures the percentage of each backscatter measurement that falls over land and only removes those measurements with contaminated regions larger than 1% of the power weighted area of the measurement. In version 4, the actual backscatter contribution from land was computed rather than just the percentage of area contaminated and rather than throwing out all "contaminated" measurements, measurements with moderate contamination were "corrected".

In this presentation, we discuss a method for improved quality control of the product which flags poor quality wind vector cells based upon distance from coast. The distance threshold used varies geographically and with instrument viewing geometry due to shape of coast, and observed coastal anomalies. The flag is trained using comparisons to buoys and biases with respect to oceanward winds. LCR and LCRES biases are compared. Regions with larger LCRES-LCR corrections are presumed to be error-prone. An empirical approach was used because of the difficulty in addressing myriad sources of error such as adverse coastal shape, marshes, heavy shipping, or land reclamation. The version 4.0 QuikSCAT data can be found at https://podaac.jpl.nasa.gov/dataset/QSCAT_LEVEL_2B_OWV_COMP_12_KUSST_LCRES_4.0 .

The work reported here was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.