Overview
Starting in the mid-1980’s, direct broadcast satellite imagery has been acquired at ground stations located in Australia and Antarctica on a daily basis. Building on the archives and processing expertise of CSIRO and the Bureau of Meteorology, the Integrated Marine Observing System (IMOS) has made these data available as a consistently processed, calibrated and formatted archive of satellite sea surface temperature (SST) products for the Australasian region (IMOS, 2018). The collection consists of all HRPT overpasses recorded in the Australian and Antarctic region from Advanced Very High Resolution Resolution Radiometer (AVHRR) sensors aboard all operational NOAA Polar Orbiting Environmental Satellites (POES, NOAA-9 to 19) from January 1992 to the present, “stitched” and geolocated (King, 2003), and stored with full resolution (1.1 km at nadir).
SST values are derived by regressing the AVHRR brightness temperatures to SST observations from drifting and tropical moored buoys in the Australasian region (Griffin et al., 2017). The system smoothly and automatically corrects for changes in each AVHRR sensor's bias using a running 1-year calibration window adjusted monthly. The data are formatted and flagged according to the International Group for High Resolution SST (GHRSST) Data Specification (GDS) 2.0 revision 5 (r5) format specification (GHRSST Science Team, 2012), including time varying error estimates and quality level flags for each SST value, calculated using matchups with drifting buoy SST data and proximity to cloud, respectively. The records form a unique 30-year data set that supplies quality-assured SST values, both at native resolution (level 2) and 2 km composites (level 3) to within 2 km of coasts (Wijffels et al., 2018). All AVHRR Level 2 Pre-processed (L2P) swath data are gridded, using a method that weights the pixels by quality level, SSES and overlap area (Griffin et al., 2017), to generate 0.02o x 0.02o single swath L3U composites over two domains – Australia (70oE to 190oE, 70oS to 20oN) and the Southern Ocean (2.5oE to 202.5oE, 77.5oS to 27.5oS). The highest quality gridded swath SST estimates from multiple passes of the same satellite over the same day for either daytime or night-time data are averaged to form single sensor L3C composites, then L3S composites formed by combining data from multiple sensors over a fixed time period - 1 day, 3 days, 6 days, 14 days and 1 month. In order to obtain the most accurate IMOS AVHRR L3U, L3C or L3S SST estimates at any given grid location, it is recommended to choose the highest quality level (5) and subtract the corresponding sses_bias value at that location (Griffin et al., 2017; IMOS, 2018). An example of IMOS AVHRR Brightness Temperature (L1B) and L2P, L3U, L3C and L3S SST data is shown in Figure 1.
Figure 1: Illustration of the different levels of IMOS AVHRR SST products (L2P, L3U, L3C and L3S) over the Australian domain.
The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor on Suomi-NPP and NOAA-20 polar orbiting satellites has now superseded the AVHRR on POES satellites. To facilitate use of the wider swath and higher resolution VIIRS data (0.75 km compared with 1.1 km for Full Resolution Area Coverage AVHRR), NOAA produce real-time VIIRS L3U SST on the IMOS 0.02o x 0.02o grid (NOAA CoastWatch, 2018). The Bureau of Meteorology have composited the NOAA VIIRS L3U data, following the method in Griffin et al. (2017), to produce daily day/night L3C composites of VIIRS data on the IMOS grid and domain. The NPP and NOAA-20 VIIRS L3U data are composited, based on quality and uncertainty estimates, with AVHRR SST data from operational POES and MetOp satellites to construct the IMOS "Multi-sensor L3S" product suite (Govekar et al., 2022; Griffin et al., 2017). This has resulted in improvements to overall quality, accuracy and coverage of IMOS L3S composites (Govekar et al., 2022). To best use these IMOS L3C and Multi-sensor L3S products it is recommended that users select data with quality level 4 or higher and subtract sses_bias.
Infrared sensors on geostationary satellites have provided accurate SSTs at high temporal resolution over the Australian region since 2006, from the Japanese Meteorological Agency’s (JMA’s) Himawari series of satellites - with hourly, 4 km SST observations from Himawari-6 (aka MTSAT-1R) (e.g. Zhang et al. 2016a, 2018) and Himawari-7 (aka MTSAT-2), and now 10 minute, 2 km observations from the currently operational Himawari-8 (Kurihara et al., 2016; Griffin and Majewski, 2016), which when composited over a number of hours enables filling in gaps due to transient cloud (e.g. Beggs et al., 2018). Diurnal warming of the surface ocean can be measured using day-only and night-only IMOS AVHRR L3C SST products (e.g., Zhang et al., 2016b), 5 km hourly IMOS MTSAT-1R L3U (Zhang et al. 2016a; 2018) or 2 km hourly IMOS Himawari-8 L3C (Beggs et al., 2018).
If users require a coarser spatial resolution, but gap-free, Level 4 (L4) SST analysis over the Australian or global domain then it is suggested that they see Beggs (2021), for a selection of global L4 products and access details. Note that unlike an L2P, L3U, L3C or L3S SST product, the feature resolution (i.e., ability to resolve surface ocean features such as fronts, eddies, coastal upwelling) of an L4 SST product does not equate to the grid resolution (Fiedler et al., 2019). The Bureau of Meteorology produce regional and global L4 SST analyses ("RAMSSA" and "GAMSSA"), which are available from the NCI gy24 project and Australian Ocean Data Network (AODN) Thredds server (see Beggs, 2021 and Beggs et al., 2020 for more details).
Products Summary (qm43) lists the various IMOS Level 2 and Level 3 satellite SST products supplied via the NCI Thredds server. For more details on the IMOS GHRSST products, see Beggs (2021), IMOS (2018) and references therein.
Further information
References
Beggs, Helen (2021). Temperature. Ch 14 in Earth Observation: Data, Processing and Applications. Volume 3B—Surface Waters. CRCSI, Melbourne. pp. 245–279. ISBN 978-0-6482278-5-4. https://www.eoa.org.au/earth-observation-textbooks
Beggs, H., Griffin, C., Brassington, G. and Govekar, P. (2018) Measuring coastal upwelling using IMOS Himawari-8 and Multi-Sensor SST, Presented as a poster at ACOMO 2018 Workshop, Canberra, Australia, 9th - 11th October, 2018. http://imos.org.au/fileadmin/user_upload/shared/SRS/SST/Beggs_ACOMO_Poster_Coastal_Upwelling_20181004.pdf
Beggs, H., Griffin, C. and Govekar, P. (2019). New IMOS multi-sensor sea surface temperature composites provide better coverage and accuracy, IMOS web article, 21 February 2018, http://imos.org.au/fileadmin/user_upload/shared/SRS/SST/Beggs_2019_IMOS_Multi-sensor_L3S_article_21Feb2018.pdf
Beggs, Helen, Lixin Qi, Pallavi Govekar and Christopher Griffin (2020) Ingesting VIIRS SST into the Bureau of Meteorology's Operational SST Analyses, In: Proceedings of the 21st GHRSST Science Team Meeting, Virtual Meeting hosted by EUMETSAT, 1st – 4th June 2020. p. 104-110. https://www.ghrsst.org/meetings/21st-ghrsst-international-science-team-meeting-g-xxi/
Fiedler, E.K., Mao, C., Good, S.A., Waters, J., and Martin, M.J. (2019). Improvements to feature resolution in the OSTIA sea surface temperature analysis using the NEMOVAR assimilation scheme. Quarterly Journal of the Royal Meteorological Society, 145(725), 3609–3625. https://doi.org/10.1002/qj.3644
GHRSST Science Team (2012). The Recommended GHRSST Data Specification (GDS) 2.0, document revision 5, available from the GHRSST International Project Office, 2012, pp 123. https://www.ghrsst.org/wp-content/uploads/2016/10/GDS20r5.pdf
Govekar, Pallavi, Jonathan Mittaz, Christopher Griffin and Helen Beggs (2021) Himawari-8 and Multi-sensor sea surface temperature products and their applications, Presented as a poster at the 22nd GHRSST Science Team Meeting, Virtual Meeting hosted by EUMETSAT, 7th – 11th June, 2021. https://www.foo.org.au/wp-content/uploads/2021/11/Govekar_FOO_2021.pdf
Govekar, Pallavi, Christopher Griffin and Helen Beggs (2022) Multi-sensor Sea Surface Temperature products from the Australian Bureau of Meteorology, Remote Sensing, 14, 3785. https://doi.org/10.3390/rs14153785
Griffin, C., Beggs, H. and Majewski, L. (2017). GHRSST compliant AVHRR SST products over the Australian region – Version 1, Technical Report, Bureau of Meteorology, Melbourne, Australia, 151 pp. http://imos.org.au/fileadmin/user_upload/shared/SRS/SST/GHRSST-DOC-basic-v1.0r1.pdf
Griffin, C. and Majewski, L. (2016). GHRSST Himawari-8 SST at Australian Bureau of Meteorology, Presented at the 17th GHRSST Science Team Meeting, Washington DC, USA, 6th to 19th June 2016. https://imos.org.au/fileadmin/user_upload/shared/SRS/SST/GriffinMajewskiGHRSSTXVIIHW8SST6Jun2016FINAL.pdf
IMOS (2018). IMOS Satellite Remote Sensing SST Data Web Page. http://imos.org.au/facilities/srs/sstproducts/sstdata0/
King, E. A. (2003). The Australian AVHRR Data Set at CSIRO/EOC: Origins, Processes, Holdings and Prospects, CSIRO Earth Observation Centre Report 2003/04, Canberra, Australia. http://www.eoc.csiro.au/tech_reps/2003/tr2003_04.pdf
Kurihara, Y., Murakami, H., and Kachi, M. (2016). Sea surface temperature from the new Japanese geostationary meteorological Himawari-8 satellite, Geophys. Res. Lett., 43, 1234-1240, https://doi.org/10.1002/2015GL067159
NOAA CoastWatch (2018). ACSPO Global SST from VIIRS Web Page: https://coastwatch.noaa.gov/cw/satellite-data-products/sea-surface-temperature/acspo-viirs.html
Wijffels, S.E., Beggs, H., Griffin, C., Middleton, J.F., Cahill, M., King, E., Jones, E., Feng, M., Benthuysen, J.A., Steinberg, C.R., and Sutton, P. (2018). A fine spatial scale sea surface temperature atlas of the Australian regional seas (SSTAARS): seasonal variability and trends around Australasia and New Zealand revisited, J. Marine Systems, 187, 156-196. https://doi.org/10.1016/j.jmarsys.2018.07.005
Zhang, H., Beggs, H., Majewski, L., Wang, X.H., and Kiss, A.E. (2016a). Investigating Sea Surface Temperature Diurnal Variation over the Tropical Warm Pool Using MTSAT-1R Data. Remote Sensing Environment, 183, 1-12. http://www.sciencedirect.com/science/article/pii/S003442571630195X
Zhang, H., Beggs, H., Wang, X.H., Kiss, A.E., and Griffin, C. (2016b). Seasonal patterns of SST diurnal variation over the Tropical Warm Pool region, J. Geophys. Res. Oceans, 121, doi:10.1002/2016JC012210. http://onlinelibrary.wiley.com/doi/10.1002/2016JC012210/epdf
Zhang H., Beggs, H., Wang, X.H., Rodriguez, J., Thorpe, A.L., Brunke, M., Majewski, L., Kiss, A.E., and Gentemann, C. (2018). Comparison of SST Diurnal Variation Models over the Tropical Warm Pool, J. Geophys. Res. Oceans, 123. http://dx.doi.org/10.1029/2017JC013517