On February 16th 2016, just before 6 pm, the third Sentinel of the Copernicus programme, Sentinel-3A was launched. It was joined in space by its twin, Sentinel-3B, twenty-six months later on the 25 April 2018.
Both of the Sentinel-3 satellites have four scientific instruments:
- Sea and Land Surface Temperature Radiometer (SLSTR) measures temperatures of both the sea and land. This instrument has 9 spectral bands with a spatial resolution of 500 m for visible/near-infrared wavelengths and 1 km for the thermal wavelengths, and has swath widths of 1420 km at nadir and 750 km looking backwards. Itâ€™s worth noting that two thermal infrared spectral wavebands are optimised for fire detection.
- Ocean and Land Colour Instrument (OLCI) has 21 spectral bands (400â€“1020 nm) focussed on ocean colour and vegetation measurements. All bands have a spatial resolution of 300 m with a swath width of 1270 km.
- Synthetic Aperture Radar Altimeter (SRAL) which has dual frequency Ku and C bands. It offers 300 m spatial resolution after SAR processing.
- Microwave Radiometer (MWR) dual frequency at 23.8 & 36.5 GHz, it is used to derive atmospheric column water vapour measurements for correcting the SRAL instrument.
For six months after the launch of Sentinel-3B, the two satellites flew thirty seconds apart during its commissioning phase, after which Sentinel-3B was moved into its final orbit in October. Now the twin satellites both have an altitude of just over 800 km, although they are one hundred and forty degrees apart which means they offer a temporal resolution of less than two days for the OLCI, and less than one day for SLSTR at the equator.
Whilst the main objectives of the mission are focussed on sea surface topography, sea and land surface temperature, and ocean and land surface colour; the SRAL also offers opportunities to measure the height of inland water bodies, and within Pixalytics weâ€™ve begun incorporating this data stream into our Water Height product, sitting alongside the data from the Jason series of satellites.
Weâ€™ve also started to incorporate Sentinel-3 into our land surface temperature product suite, and weâ€™re not alone in using the data from these satellites. Â A significant number of papers are starting to be published using Sentinel-3 data, and ESA is also releasing various images. Picking out examples from the last few months gives:
- Last summer ESA used the OLCI instrument to show the changing colour of Europeâ€™s vegetation during the dry summer months with both images and videos which can be seen here.
- Last month ESA released images from the OLCI instrument captured snowfall in Turkey across both its major cities such as Ankara and some of the more remote areas. Whilst at the end of January EUMETSAT released images from the United States from the really cold temperatures they had.
- Last week the BBC weather forecasts showed a combined Sentinel-3A and 3B image over the UK with the relatively cloud free skies.
- OLCI was used by Xue et alÂ in the paperÂ Optical Classification of the Remote Sensing Reflectance and Its Application in Deriving the Specific Phytoplankton Absorption in Optically Complex Lakeswhich was published by Remote Sensing in January 2019.
- Remote Sensing of Water Quality Parameters over Lake Balaton by Using Sentinel-3 OLCI was published by Blix et alÂ in Water in October 2018.
- Persistent Hot Spot Detection and Characterisation Using SLSTR by Caseiro et al which was published in Remote Sensing in July 2018.
For anyone who is working with Sentinel-3 data you might be interested to know that the Remote Sensing Journal is planning a special issue this year focused on the presentation of results derived from the OLCI and SLSTR instruments in relation to remote sensing of the atmosphere, plantâ€™s surface including ocean, land, snow and ice, as well as retrieval algorithms, instrument calibration and validation of products. The abstract deadline is 31st May and more details can be found here.
Sentinel-3 has already showed that it is going to be aÂ valuable resource in its short time as a twin constellation, and weâ€™re excited to see what innovations and scientific research can be produced from this pair of satellites.