This VIIRS SST data are produced using the NOAA Advanced Clear-Sky Processor for Ocean (ACSPO) SST system, from the afternoon SNPP and soon to be launched JPSS-1 (NOAA-20) satellites, in two formats: L2P and L3U (uncollated). The data are reported in 10min granule files in NetCDF4 format, compliant with the GHRSST Data Specifications v2 (GDS2). There are 144 granules per 24hr interval, with a total data volume of ~25GB/day for L2P, and ~0.4GB/day for L3U.
The near real-time (NRT) data have been operationally produced by the NOAA Data Exploitation (NDE) using the official enterprise ACSPO algorithms. The NRT L2P data have been produced using ACSPO v2.30 (20 May 2014 - 19 May 2015), v2.40 (19 May 2015 - 14 Sep 2017) and v2.41 (14 Sep 2017 - pr). The NRT L3U data have been produced using ACSPO versions 2.40 (19 May 2015 - 14 Sep 2017) and 2.41 (14 Sep 2017 - pr). A 2-week rotated buffer of the NRT data is provided here on Coast Watch, whereas the full data are available from PO.DAAC and NOAA NCEI (see links under "Data Access"). Development of ACSPO v2.50 and v2.60 is currently underway.
The Reanalysis version 1 (RAN1) product was produced at STAR using ACSPO v2.40, in conjunction with the U. Wisconsin group led by Liam Gumley. L2P RAN1 data covered a period from 1 Mar 2012 - 5 Dec 2015. The L3U gridded data additionally cover period from 5 Dec 2015 - pr, using NRT L2P data available in PO.DAAc and NCEI. The UW Team used a converter from RDR (L0) to SDR (L1b), whose origin and performance have not been independently verified. Also, there have been difficulties processing RDR-to-SDR data before 1 Mar 2012 (recall that VIIRS cryoradiator doors on S-NPP opened on 18 Jan 2012, after which time RDR data became available). The algorithms used in VIIRS RAN1, are similar to those described in (Ignatov et al., 2016) for AVHRR GAC, except fixed regression coefficients were used (in contrast with variable coefficients for AVHRR). Currently, the RAN1 data are only available on this Coast Watch site. Work is underway to reprocess the full SNPP VIIRS record with improved RDR-to-SDR conversion, and ACSPO L2P and L3U algorithms, and create VIIRS RAN2.
ACSPO retrievals are made in full VIIRS swath (~3,000 km). For data assimilation applications (such as production of L4 analyses, especially those that blend satellite and in situ data), correction for the Sensor-Specific Error Statistics (SSES; reported in ACSPO files; Petrenko et al., 2016) biases is strongly recommended.
In each valid water pixel (defined as ocean, sea, lake or river, up to 5km inland; note that in "invalid" pixels, defined as those with >5km inland, fill values are reported), the following layers are reported in both L2P and L3U, among others: SSTs derived using multi-channel SST (MCSST; night) and Non-Linear SST (NLSST; day) algorithms (Petrenko et al., 2014); ACSPO clear-sky mask (ACSM; provided in each pixel as part of l2p_flags; Petrenko et al., 2010); SSES bias and standard deviation (Petrenko et al., 2016); NCEP wind speed; and ACSPO SST minus reference (Canadian Met Centre L4 SST). For L2P, layers of brightness temperatures (BTs) in M12, 15, and 16 are also reported, for those users interested in direct "radiance assimilation" (e.g., NOAA NCEP, NASA GMAO).
Only ACSM "confidently clear" pixels (equivalent to GDS2 "quality level"=5; QLs are also reported for each pixel) should be used. The ACSM also provides day/night, land, ice, twilight, and glint flags. Note that users of ACSPO data have the flexibility to ignore the ACSM, derive their own clear-sky mask, and use BTs and SSTs in those pixels. They may also ignore ACSPO SST, and derive their own SSTs from the original BTs.
Both L2P and L3U SSTs are monitored and validated against in situ data (Xu and Ignatov, 2014) in SQUAM (Dash et al., 2010) and ARMS systems, and BTs are monitored in MICROS (Liang and Ignatov, 2011).
Afternoon: S-NPP / VIIRS
Measurement Oceans > Sea Surface Temperature > Sub-skin SST
NRT L2P: 20 May 2014 to present
NRT L3U: 19 May 2015 to present RAN L2P: 1 Mar 2012 to 5 Dec 2015
RANL3U: 1 Mar 2012 to present (after 5 Dec 2015, NRT L2P available in PO.DAAC and NCEI have been gridded)