Sentinel-3 Mission Overview
The main objective of the Sentinel-3 mission is to measure sea surface topography, sea and land surface temperature, and ocean and land surface colour with high accuracy and reliability to support ocean forecasting systems, environmental monitoring and climate monitoring. The mission definition is driven by the need for continuity in provision of ERS, ENVISAT, and SPOT-VGT vegetation data, with improvements in instrument performance and coverage.
Sentinel-3 carries four main instruments on-board:
- OLCI: Ocean and Land Colour Instrument
- SLSTR: Sea and Land Surface Temperature Radiometer
- SRAL: SAR Radar Altimeter
- MWR: Microwave Radiometer.
Terrascope Sentinel-3 data products will comprise those acquired from OLCI and SLSTR, the instruments’ characteristics are described below.
Instrument characteristics
Ocean and Land Colour Instrument (OLCI)
The OLCI instrument baseline is the successor to ENVISAT MERIS with additional spectral channels, different camera arrangements and simplified on-board processing. The OLCI is a push-broom instrument with five camera modules sharing the field of view. The field of view of the five cameras is arranged in a fan-shaped configuration in the vertical plane, perpendicular to the platform velocity. Each camera has an individual field of view of 14.2° and a 0.6° overlap with its neighbours. The whole field of view is shifted across track by 12.6° away from the sun to minimise sun glint effects.
Figure 1: OLCI observation configuration.
This “native” acquisition resolution of approximately 300 m is the one used to compute the product grid of Full Resolution (FR) product. A Reduced Resolution (RR) processing mode provides Level-1B data at sampling rates decreased by a factor of four in both spatial dimensions resulting to a spatial resolution of approximately 1.2 km. OLCI is equipped with on-board calibration hardware based on three sun diffusers: two “white” diffusers dedicated to radiometric calibration and one dedicated to spectral calibration, with spectral reflectance features.
Sea and Land Surface Temperature Radiometer (SLSTR)
The principal aim of the SLSTR instrument mission on-board SENTINEL-3 is to maintain continuity with the (Advanced) Along-Track Scanning Radiometer (A)ATSR series of instruments. The design supports this by incorporating the basic functionality of AATSR, with the addition of some new, more advanced, features. These include a wider swath, new channels (including two channels dedicated to fire detection), and higher spatial resolution in some channels. The Sea Surface Temperature (SST) is obtained by means of a highly accurate calibration of the three infra-red channels at 3.74, 10.85, and 12 µm (S7-S8-S9) used for water vapour atmospheric absorption correction (split window during day and triple window during night) and observation of the same ground pixel through two atmospheric path views for aerosol correction.