Satellite Sea Surface Temperature Validation group (ST-VAL)
The development of the Sensor Specific Error Statistics (SSES) is one of the activities of the Satellite Sea Surface Temperature Validation (ST-VAL) Technical Advisory Group (TAG). This group was established to look at all aspects of satellite SST validation: from the reference data itself, to the challenges which occur when comparing these locally representative reference observations to satellite data, to the ongoing refinement of the uncertainty estimates.
Diurnal Variability Working Group (DVWG)
Diurnal variability of the SST results from the daily cycle of sunlight which warms the upper ocean. While the variations are typically small due to mixing from the wind, under light winds and strong insolation, the surace temperature can warm by more than 5 K in extreme cases. Diurnal variability matters to those who wish:
- To make optimum use of SST data captured at different times of day
- To make accurate estimates of ocean-atmosphere fluxes that are modified by any diurnal warming cycle
- To estimate the skin SST at a particular time of day
To provide a value reprsentative of a specific depth or the heat content of the upper layer of the ocean, the observations should be adjusted as a function of depth and time. Neglecting these variations will lead to biases that can affect ocean forecasting models that assimilate SST observations. The instantaneous radiative and turbulent heat fluxes between ocean and atmosphere are fundamentally functions of skin SST. An analysis of the evolution of the skin temperature through the day is therefore both supportable by satellite observations and useful in improving ocean-atmosphere flux estimates. The diurnal variability working group is attempting to better understand the factors influencing diurnal warming and develop improved methods for predicting the amount of warming present at different times and depths.
High Latitude Technical Advisory Group (HL-TAG)
The high latitude regions are characterized by a lack of in situ observations, decreasing ice cover and strong sensitivity to climate changes. It is therefore important to secure the availability of accurate and reliable satellite SST observations in the high latitudes, which are the main objectives for the GHRSST High Latitude Technical Advisory Group (HL-TAG). The dry atmosphere, presence of sea ice in the Marginal Ice zone, the extended periods with cloud cover and the lack of in situ observations makes the retrieval of sea surface temperature observations from satellite a challenging task. The HL-TAG focuses upon validating and improving the satellite retrievals in the high latitude region(s). In addition, the HL-TAG facilitates the use of existing in situ observations and encourages the community to deploy new drifting buoys and other in situ observations.
The Inter-Comparison Technical Advisory Group (IC-TAG)
The aim of the IC-TAG is to develop international collaboration in this field in order to assess and inter-compare the different L4 analyses, and to provide uncertainty estimates on both the analyses and observational products, and appropriate guiding of the users. There are currently three systems used for inter-comparing the various L4 analyses within the IC-TAG:
- The GHRSST Multi-Product Ensemble (GMPE) system (http://ghrsst-pp.metoffice.com/pages/latest_analysis/sst_monitor/daily/ens/index.html)
- Felyx (http://hrdds.ifremer.fr/)
- The SST Quality Monitor (SQUAM) system (http://www.star.nesdis.noaa.gov/sod/sst/squam/)
The Estimation and Retrievals Working Group (EARWiG)
is exploring the fundamental issues surrounding retrieval of SST from top-of-atmosphere radiances. These include the effects of cloud detection errors as well as other known issues such as geographical and aerosol related effects. Regionally varying aerosol and moisture contents add errors (biases) to the SST estimate from infrared sensors. For microwave sensors, retrieval issues include emissivity, calibration and rain flagging, as well as radio frequency interference effects. EARWiG compares and develops different cloud detection and SST retrieval methods, with the objective to generate more accurate GHRSST L2P products.
Inland Waters Working Group (IWWG)
The GHRSST IWWG coordinates international activities related to the treatment of inland surface water temperature and land masks in GHRSST data products. The interaction of the atmosphere with the underlying surface is strongly dependent on the surface temperature and its time-rate-of-change. Most NWP systems assume that the water surface temperature can be kept constant over the forecast period. The assumption is doubtful for small-to-medium size relatively shallow lakes, where the diurnal variations of the surface temperature reach several degrees. A large number of such lakes will become resolved-scale features as the horizontal resolution is increased. Apart from forecasting the lake surface temperature, its initialization is also an issue. Lakes strongly modify the structure and the transport properties of the atmospheric surface layer above.
Rescue & Reprocessing of Historical AVHRR Archives (R2HA2) Working Group
Five Advanced Very High Resolution Radiometers (AVHRR) have been flying on NOAA polar-orbiting satellites (and more recently the European polar-orbiting satellite, METEOSAT) since 1981. Because there was no encryption of the down-linked data, anyone with a receiving station could acquire these data. As a result a number of organizations have set up HRPT receiving stations over the years and collected a subset of the passes seen by the station. These data have been archived in a variety of formats and on a variety of media ranging from 9 track tape to DVDs. Many of these receiving stations are situated in coastal areas, acquiring passes covering shelf and slope waters that are of general interest to the oceanographic community. The Rescue & Reprocessing of Historical AVHRR Archives (R2HA2) Working Group has been founded to locate these distributed data, re-process with a community-consensus algorithm and store in a consistent format on modern media, to rescue them for research on long-term SST changes.
Climate Data Records Technical Advisory Group (CDR-TAG)
The GHRSST Climate Data Records Technical Advisory Group (CDR-TAG) coordinates the global production of SST Climate Data Records (CDR) extending back to 1981. Through interactions with the GCOS SST and Sea Ice Working Group, ESA’s Climate Change Initiative, the NOAA CDR Program, and members of the global climate SST community, the RAN-TAG has developed a comprehensive SST Essential Climate Variable (ECV) Framework for SST. This framework reflects the fact that no single SST CDR product can meet all users’ needs and illustrates the requirement for a coordinated suite of SST CDR products instead. The RAN-TAG works to ensure that all GHRSST operational and delayed mode data sets are archived and made available at the NODC LTSRF, and that the many groups developing CDRs around the world work together smoothly and efficiently, minimizing unnecessary duplication of effort and sharing scientific advances and product development experience.
Applications and User Services Technical Advisory Group (AUS-TAG)
The main goal of the AUS-TAG is to facilitate usage of GHRSST products across a broad user spectrum. Besides answering the user questions directly on an individual basis, AUS-TAG also maintains the GHRSST User’s Manual, including data access and descriptions. Another responsibility of the AUS-TAG is to maintain and develop methods for data discovery.
Data Assembly and Systems Technical Advisory group (DAS-TAG)
The GHRSST Data Assembly and Systems TAG is responsible for the day-to-day operational specification and management of GHRSST data products and services. In practice, this involves the specification and control of all aspects of data archive, dissemination, file level and discovery metadata, international standards conformance, quality control and assurance issues, product content, amongst many others. The DAS-TAG is a dynamic team drawing on the collective resources of an international membership that is actively involved in satellite and in situ data management issues.