QuikSCAT Level 1C Averaged Sigma-0 and Winds from Non-spinning Antenna Version 2.0
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|Description||This dataset is Version 2 of the geo-located and averaged Level 1B Sigma-0 measurements and wind retrievals from the SeaWinds on QuikSCAT platform, initiated in the months following the failure of the rotating antenna motor on 22 November 2009, using the various incidence angles at which QuikSCAT was pointed during the time period from November 2009 until present. Incidence angles were varied in order to cross-calibrate the Oceansat-2 and RapidScat scatterometers and to extend the known Ku-band geophysical model function. The averaging of the L1B input data combined with the wind vector processing results are both contained in this product referred to hereafter as Level 1C (L1C). The fixed and repointed beam processing is relative to either the one corresponding to the vertically polarized "outer" beam or the other corresponding to the horizontally polarized "inner" beam. The Sigma-0 values from the fixed operating beam for each frame are averaged to a single value representing approximately 50 samples. The data points are land flagged, collocated with ECMWF surface winds, and have climatological nadir attenuations provided for the location and time of the data (not applied to the sigma0). The following enhancements have been applied in the Version 2 re-processing: 1) the GMF has been updated (QNS2016a) to make use of ECMWF nowcast 1x1 degree resolution wind direction information for the entire historical data record; 2) the new QNS2016a GMF leverages a calibration adjustment from Remote Sensing Systems (RSS) resulting in a consistently lower Normalized Radar Cross Section (NRCS or Sigma-0) measurements that establishes a Sigma-0 bias of -0.25 dB (-5.9% linear scale) compared to the L1C Version 1 data; 3) the new QNS2016a GMF also applies an azimuthal modulation that is decreased by several tenths of a dB (for Sigma-0) in variation with wind speed; this results in a more consistent wind speed retrieval comparison between "non-spinning" and "spinning" modes of the QuikSCAT instrument; 4) spacecraft attitude was re-estimated using slice data over multiple orbits as a replacement for lost echo-tracking capability during the "non-spinning" mode of the instrument; this new attitude estimation follows an unpublished manual technique that leverages the echo power of individual slice observations; since only a small subset of slice observations are analyzed, rapid variations in attitude are not captured; 5) continues data production beyond October 2016 through the end of mission on 30 August 2018. Retrieved wind directions are only slightly different from ECMWF values and should not be considered an independent measurement of wind direction. Retrieved wind speeds do not depend significantly on ECMWF speeds as evidenced by the fact that they agree closely with WindSAT polarimetric radiometer speeds whenever WindSAT and ECMWF disagree. The Sigma0 values have also been corrected for scan loss (due to the fact that the antenna does not scan) and for X-factor changes due to repointing.|
|Measurement||SPECTRAL/ENGINEERING > RADAR > SIGMA NAUGHT > None|
OCEANS > OCEAN WINDS > SURFACE WINDS > Ocean Surface Wind Vectors
Northernmost Latitude: 89.875 degrees
Southernmost Latitude: -89.875 degrees
Westernmost Longitude: -180 degrees
Easternmost Longitude: 180 degrees
Time Span: 2010-Jul-16 to 2018-Aug-30
Granule Time Span: 2010-Jul-16 to 2018-Aug-30
|Resolution||Spatial Resolution: 25 km (Along) x 25 km (Across)|
Ellipsoid: WGS 84
|Swath Width||25000 m|
|Temporal Repeat (Nominal)||12 Hour|
|Temporal Repeat (Min)||1.7 Hour|
|Temporal Repeat (Max)||4 Day|
Name: QUIKSCAT (QUIKSCAT)
Orbit Period: 100.93 minutes
Inclination Angle: 98.6 degrees
Ascending Node: 2010-Jul-16 23:06:19
Name: SeaWinds Scatterometer (SEAWINDS)
Swath Width: 1800 km
Description: SeaWinds is a Ku-band (13.4 GHz) Scatterometer which features a single circular scanning dish antenna to provide pencil-beam measurements, as opposed to the common fan beam design as seen with other spaceborne scatterometers. The pencil-beam design has several key advantages over the more common fan beam design: higher signal-to-noise ratio, smaller size, and superior coverage. The SeaWinds single antenna utilizes twin offset feeds, thus providing two pencil-beam footprint paths with an elliptical sampling footprint of approximately 25 km (in azimuth) by 37 km (in look/range direction); these pencil beams have opposing polarizations (i.e., vertical and horizontal), thus achieving dual-polarization. The SeaWinds instrument provides a full 1800 km-wide swath coverage (including the nadir region), which allows for a nominal daily measurement coverage of 90% over the ice-free oceans.
|Project||Quick Scatterometer (QUIKSCAT)|
|Data Provider||Creator: JPL|
Release Place: PO.DAAC
Release Date: 2019-Feb-13
|Keyword(s)||ocean, roughness, ocean roughness, radar, backscatter, normalized radar cross-section, normalized radar cross section, nrcs, sigma-0, sigma0, sigma naught, dB, L1C, level 1C, 1C, scatterometer, quikscat, qscat, seawinds, non-spinning, averaged, wind, wind speed, vector, wind vector, ocean wind, ocean winds, winds, vectors, wind vectors, surface, v2, v2.0, version 2, version 2.0|
Questions related to this dataset? Contact email@example.com
|Format (Compression)||RAW (NONE)|
Read software provided in MATLAB and Python.
|L1B SIS Document||https://podaac-tools.jpl.nasa.gov/drive/files/allData/quikscat/L1B/v2/docs/L1B_SIS_200609.pdf|
Software Interface Specifications for L1B
|QuikSCAT Known Problems and Issues||http://podaac.jpl.nasa.gov/OceanWind/QuikSCAT/SeaWinds-QuikSCAT_KnownProblems|
Web Page Consisting of Known Problems, Issues, and Data Gaps
|QuikSCAT Level 1C Dataset Known Issues and Updates||https://podaac.jpl.nasa.gov/forum/viewtopic.php?f=16&t=391|
PO.DAAC Forum Topic on Known Issues and Updates to the QuikSCAT L1C Dataset. Users may post questions or comments directly to this Forum posting.
|Citation||JPL. 2019. QuikSCAT Level 1C Averaged Sigma-0 and Winds from Non-spinning Antenna Version 2.0. Ver. 2.0. PO.DAAC, CA, USA. Dataset accessed [YYYY-MM-DD] at https://doi.org/10.5067/QSNON-L1CA2.
For more information see Data Citations and Acknowledgments.