Sea and Land Surface Temperature Radiometer

Sea and Land Surface Temperature Radiometer
Name	Sea and Land Surface Temperature Radiometer
Acronym	SLSTR
Operator	European Space Agency
Missions	Sentinel-3
Type	Multispectral scanning radiometer
Launched	2016
Wavelength	Thermal infrared and visible
Resolution	~500 m (thermal)

Sea and Land Surface Temperature Radiometer

The Sea and Land Surface Temperature Radiometer is a satellite-borne imaging radiometer developed for global Earth observation and Copernicus Programme operational services. It provides sustained measurements of surface temperature over Atlantic Ocean, Pacific Ocean, Indian Ocean, coastal zones and continental land, supporting meteorology, oceanography, climate change monitoring and maritime safety applications within the European Space Agency Sentinel-3 mission framework.

Overview

The instrument was conceived during collaborations among European Space Agency, Thales Alenia Space, Airbus Defence and Space, DLR and national agencies like UK Space Agency and Centre national d'études spatiales to meet requirements from Global Climate Observing System, Group on Earth Observations and Committee on Earth Observation Satellites. Designed to complement instruments such as AATSR, AVHRR, MODIS, VIIRS and Landsat 8 payloads, it delivers continuity for long-term records used by Intergovernmental Panel on Climate Change, World Meteorological Organization and regional services like Copernicus Climate Change Service.

Instrument Specifications and Design

The radiometer comprises dual telescopes and a pushbroom scanner with detectors spanning thermal and visible bands, integrating heritage from Advanced Along-Track Scanning Radiometer and innovations from Sentinel series engineering teams. Optical assemblies and cryogenic subsystems were produced by industrial partners including Thales Alenia Space and tested at facilities such as European Space Research and Technology Centre and VTT Technical Research Centre of Finland. Electronics and focal plane arrays were developed with involvement from Leonardo S.p.A., OHB SE, SRON and academic groups at University of Leicester, Institut d'Astrophysique Spatiale and University of Bologna. Key parameters include thermal infrared channels near 3.7 µm and 11 µm, mid-wave channels, visible/near-infrared channels for cloud screening, and along-track stereoscopic capability for sea surface temperature accuracy, with spatial resolutions designed to match Sentinel-3 altimetry, radiometry and SAR instruments.

Operating Principles and Measurement Techniques

SLSTR functions by measuring top-of-atmosphere radiance in multiple spectral bands, employing radiometric calibration hardware and internal blackbody references derived from designs used in AATSR and MODIS. The instrument exploits dual-view geometry—nadir and oblique views—similar to techniques pioneered on ATSR-2 for atmospheric correction and aerosol retrievals used by organizations such as Met Office and ECMWF. Algorithms for retrieval combine physics-based radiative transfer models from groups like Rothamsted Research and KNMI with statistical approaches developed at University of Oxford, University of Reading and CNES to separate surface emission from atmospheric effects, using inputs from ancillary sensors like GOME-2, SLSTR concurrent measurements, and meteorological analyses from ECMWF and NOAA.

Calibration and Validation

Pre-launch calibration leveraged facilities at ESTEC, RAL Space and national metrology institutes including PTB and LNE. On-orbit calibration combines onboard blackbodies, deep space views, and vicarious methods using fiducial sites such as Sahara Desert, Baker Island, Ibiza, Svalbard and maritime buoys from Global Ocean Observing System and Argo floats. Validation campaigns have been coordinated with programs run by NOAA National Centers for Environmental Information, NASA Jet Propulsion Laboratory, EUMETSAT, Met Office and research projects at Plymouth Marine Laboratory, Scripps Institution of Oceanography and Ifremer. These activities compare SLSTR products against reference measurements from radiometers on flux towers, drifting buoys, shipborne instruments and airborne campaigns like AVIRIS and POLDER deployments to quantify uncertainty and bias.

Data Products and Applications

Products include Level-1 radiances, Level-2 sea and land surface temperature maps, cloud flags, aerosol optical depth estimates and fire radiative power outputs. These feed into operational services: sea surface temperature assimilation for ECMWF and UK Met Office models, coastal monitoring for European Environment Agency, Fisheries and Oceans Canada collaborations, and disaster response for agencies like Copernicus Emergency Management Service. Research applications span studies referenced by IPCC assessments, assimilation in ocean forecast systems used by Mercator Ocean International, glacier melt analyses for Norwegian Polar Institute, agricultural monitoring for Food and Agriculture Organization, and emissions detection aligned with United Nations Environment Programme initiatives.

Mission Implementations and History

First flown on Sentinel-3A launched in 2016, the radiometer continues on Sentinel-3B and subsequent Sentinel-3 series spacecraft, forming part of the Copernicus Programme operational constellation. Development followed predecessor missions including ERS-2, Envisat and instruments like AATSR and benefitted from lessons learned in missions such as NOAA-20 and Suomi NPP. The program involves international coordination among European Commission, ESA, EUMETSAT and national space agencies; routine ground segments at ESRIN, ESOC and EUMETSAT process and distribute products to users like EMSR, CMEMS and national meteorological services. Continuous upgrades to processing chains, calibration methodologies and validation networks have been implemented through projects funded by Horizon 2020 and partnerships with institutions including CSIC, CNR, IMR and universities across Europe and beyond.

Category:Remote sensing instruments