| Service | Resource Locator |
|---|---|
| FTP | ftp://ftpcoastwatch.noaa.gov/pub/socd2/coastwatch/sst/nrt/avhrr_frac/ |
| THREDDS | https://coastwatch.noaa.gov/thredds/socd/coastwatch/acspo/catalog_sst_acspo_frac_nrt.html |
The AVHRR FRAC SST data are produced from AVHRR/3s onboard Metop-A and -B satellites using the NOAA Advanced Clear-Sky Processor for Ocean (ACSPO) v2.41 enterprise system described in (Ignatov et al., 2016). Currently, only near-real time (NRT) L2P data are operationally produced by OSPO (with a ~3hrs latency), and corresponding 0.02° L3U (gridded uncollated) product is created at STAR (with a ~3days latency). The data are not archived (at either PO.DAAC or NCEI), and only available at this Coast watch page as a 2week rotated buffer. Work is underway to add operational production of L3U in OSPO, in near future. It is also planned to reprocess all FRAC data in STAR, back to 2006, and create ACSPO AVHRR FRAC SST RAN1.
The data are reported in 10min granule files in GHRSST Data Specifications v2 (GDS2) format, in swath projection (L2P) and 0.02° gridded L3U (U=uncollated), 144 granules per day, with a total data volume of 8GB/day for L2P and 0.4GB/day for L3U, respectively.
ACSPO retrievals are made in full AVHRR swath (~2,800 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: 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, brightness temperatures (BTs) in 3.7, 11, and 12 µm bands 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; 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 (Ding et al., 2017) systems, and BTs are monitored in MICROS (Liang and Ignatov, 2011).