Towards a Protocol for Validating Land Surface Temperature for SLSTR
Ghent, Darren1; Schneider, Philipp2; Remedios, John1
1University of Leicester, UNITED KINGDOM; 2Norwegian Institute for Air Research, NORWAY
Land surface temperature (LST) has a long heritage of satellite observations which have facilitated our understanding of land surface and climate change processes, such as desertification, urbanization, deforestation and land/atmosphere coupling. These observations have been acquired from a variety of satellite instruments on platforms in both low-earth orbit and in geostationary orbit. Retrieval accuracy can be a challenge though; surface emissivities can be highly variable owing to the heterogeneity of the land, and atmospheric effects caused by the presence of aerosols and by water vapour absorption can give a bias to the underlying LST. As such, a rigorous validation is critical in order to assess the quality of the data and the associated uncertainties.
A validation protocol (Schneider et al., 2012) for satellite-based LST has recently been developed with ESA and NCEO support - the justification being to provide a standardized framework for structuring LST validation activities, which have not previously followed any uniform approach. This set of guidelines, which itself is open to feedback from the LST community, attempts to render LST consistent with many other biophysical parameters within the field of Earth Observation for structuring and standardizing calibration and validation approaches. The protocol introduces a four-pronged approach which can be summarised thus: i) in situ validation where ground-based observations are available; ii) radiance-based validation over sites that are homogeneous in emissivity; iii) intercomparison with retrievals from other satellite sensors; iv) time-series analysis to identify artefacts on an interannual time-scale.
Here we present a first application of the protocol to data from the Advanced Along-Track Scanning Radiometer (AATSR), which is an important source of satellite-retrieved LST for the near 10-year window from July 2002 to April 2012. The standard ESA LST product is assessed together with an enhanced offline LST product utilising high resolution auxiliary data produced by the University of Leicester (Ghent et al., in prep.) and is in the process of being incorporated into the Data Processing Model for the upcoming Sea and Land Surface Temperature (SLSTR) instrument on-board Sentinel-3 – the successor to AATSR. Not only will this application afford insights into the effectiveness of the protocol, it will also enable evaluation of the data record from AATSR. The lessons learnt here will strengthen the methodology in preparation for assessing whether the level-2 SL_2_LST product for SLSTR will be capable of measuring LST within the target accuracy of 1 K, and to facilitate future appraisal of the accuracy and stability of a combined (A)ATSR/SLSTR LST record.
Ghent, D., Corlett, G., and Remedios, J. Advancing the AATSR land surface temperature retrieval with higher resolution auxiliary datasets, in prep.
Schneider, P., Ghent, D., Corlett, G., Prata, F., and Remedios, J. Land Surface Temperature Validation Protocol, Report to ESA: Report No. UL-NILU-ESA-LST-LVP, 2012