Wednesday, August 24, 2016

The QuikSCAT Science Data Systems team has recently delivered an updated batch of approximately two more months of data for the Level 1C dataset, bringing the dataset time series up to 12 August 2016 (calendar day 255), as made available here: http://podaac.jpl.nasa.gov/dataset/QSCAT_L1C_NONSPINNING_SIGMA0_WINDS_V1
 
The QuikSCAT Science Data Systems team had previously discovered a subtle difference in the wind vector retrieval between spinning scatterometers (e.g. RapidSCAT, QuikSCAT before 2009) and QuikSCAT L1C (QuikSCAT nonspinning configuration). This difference resulted in a change to the Geophysical Model Function (GMF) that went into effect for the QuikSCAT L1C dataset starting with orbit 87727. Earlier orbits have less consistent wind speeds with systematic errors of 0.3 to 0.4 m/s.
 
The new QuikSCAT GMF (hereafter, QSNS2016a) was developed from nonspinning QuikSCAT data. This new GMF differs from the NSCAT2014 GMF used to retrieve the publicly available RapidScat and spinning QuikSCAT winds in two primary ways. First, there is a constant Normalized Radar Cross Section (NRCS) bias of -0.25 dB (-5.9% linear scale) with QSNS2016a producing lower NRCS values. This difference is due to a calibration adjustment applied to QuikSCAT NRCS that was consistently used in the Remote Sensing Systems (RSS) wind retrieval and GMF development, but was missing from JPL wind retrievals until recently. The second difference is that the azimuthal modulation in QSNS2016a is decreased by several tenths of dB (varying with wind speed). This reduction is consistent with differences between how winds are retrieved for nonspinning and spinning data.
 
Data files are sorted by the orbital revolution number and referenced by date and time using the following reference file: https://podaac-tools.jpl.nasa.gov/drive/files/allData/quikscat/L1C/docs/revlist_pol_incid_start_end_times.txt
 
Users who have any further questions or concerns are encouraged to visit our special QuikSCAT L1C Forum page, which also includes further details on existing and future dataset issues and updates: https://podaac.jpl.nasa.gov/forum/viewtopic.php?f=16&t=391