Question: Why are lat/lon coordinates set to 0 for the older SeaWinds on ADEOS-II and QuikSCAT L2B datasets at certain points in the swath?
Answer: The older SeaWinds on ADEOS-II and QuikSCAT L2B ocean surface wind vector datasets (including Versions 2 and below for QuikSCAT) use an outdated processing schema which assigns a null or 0 value for latitude and longitude coordinates for when a wind vector retrieval could not be performed. There are many reasons for why a wind vector retrieval could not be performed, including: excess land/ice contamination, inadequate availability of sigma-0 (i.e., the normalized radar cross-section, or what is also referred to as NRCS or backscatter), and lack of azimuth diversity. The embedded quality flags can be used to provide further distinction on this.
This issue has since been rectified in the latest Version 3 processing for QuikSCAT, in which all known latitude/longitude coordinate data (from telemetry) is made available. At this time, there is no corresponding update to the SeaWinds on ADEOS-II L2B datasets. For access and additional information on the QuikSCAT Version 3 L2B dataset, please visit: http://podaac.jpl.nasa.gov/dataset/QSCAT_LEVEL_2B_OWV_COMP_12.