Import Sentinel-3 |

# Sentinel-3

The Sentinel-3 platform has different sensors onboard. Its mission is to measure sea surface topography, sea and land surface temperature, and ocean and land surface colour with high accuracy and reliability. By these features Sentinel-3 supports ocean forecasting systems, environmental monitoring and climate monitoring.

## Sentinel-3 Data

Sentinel-3 has 3 different sensors

SLSTR
  Sea and Land Surface Temperature Radiometer - it determines global sea surface temperatures at an accuracy of better than 0.3 K. SLSTR measures in nine spectral channels and two additional bands. A 1.3 micron band aimed at cirrus detection and a 2 micron band aimed at vegetation, mineral and atmospheric corrections for very turbid waters.
OLCI
  Ocean and Land Colour Instrument - with 21 bands, a design optimised to minimise sun-glint and a resolution of 300 m over all surfaces. OLCI marks a new generation of measurements over the ocean and land. The swath of OLCI and nadir SLSTR fully overlap.
SRAL
  Synthetic Aperture Radar Altimeter - provides measurements at a resolution of approximately 300 m in SAR mode along track. SRAL is supported by a MicroWave Radiometer (MWR) and a Precise Orbit Determination (POD) package, a GPS receiver (GNSS), a DORIS instrument and a Laser Retro-Reflector (LRR).
  Note: This SRAL data is not supported by the Optical Toolbox. To work with this data it is recommended to use the Sentinel Altimetry Toolbox .

Also Envisat data is provided in Sentinel-3 like format (4th reprocessing)

MERIS
  The MEdium Resolution Imaging Spectrometer (MERIS) was a programmable spectrometer on the Envisat mission, operating in the solar reflective spectral range. Although primarily dedicated to ocean colour observations, MERIS broadened its scope of objectives to atmospheric and land surface related studies. The OLCI sensor can considered as the successor of MERIS.
AATSR
  The Advanced Along-Track Scanning Radiometer (AATSR) was one of nine instruments on board the Envisat satellite. It was the third in a series of instruments designed primarily to measure Sea Surface Temperature (SST) remotely, following on from ATSR-1 and ATSR-2 on board ERS-1 and ERS-2, respectively. All those are the ancestors of the SLSTR sensor onb board of Sentinel-3.

  IMPORTANT Note:
  Currently (S3TBX v9.0) the AATSR data in Sentinel-3 like format do not provide geo-location information in SNAP. Applying the provided data (v2.0.5 of 4th reprocessing) does not give good results. Therefore, it is better to provide the data without geo-location information.

## Notes to specific data types

### SLSTR L2 FRP

The SLTSR Level 2 Fire Radiative Power product is special in the sense that the measurement data is not supplied as raster data, instead it is stored as a vector of measurements. SNAP provides a built-in mechanism to map these vector data onto a raster that is generated on-the-fly to allow for a simple view of the spatial distributions.

Due to missing geo-location data for the stripe A/B acquisitions, the geolocation for these data is interpolated from the "in" geolocation. This incorporates a small error. If you require the exact location of the measurement data, please use the values stored in the product metadata.

## Import Data

The data is usually distributed in a zip archive. This needs to be extracted first. Afterwards the data can be imported via the respective entry in the application menu at '`File / Import / Optical Sensors / Sentinel-3`'. For SLSTR tow special options exist. Sentinel-3 SLSTR L1B (1km) and Sentinel-3 SLSTR L1B (500m). The 500m option will only open the bands which are provided at this resolution. The 1km options will resample all data to the resolution. When using the generic option, then the bands will be imported unmodified at their native resolution.
To import the data the `xfdumanifest.xml` needs to be selected in the import dialog.

Of course it is also possible to simply use the open dialog from the menu '`File / Open Product...`' or the toolbar. Here by default the generic reader is used.

Another option to open Sentinel-3 data is to drag'n'drop the `*.SEN3` folder or the `xfdumanifest.xml` files onto the Product Explorer in SNAP.

## Recommended Flags

SNAP generates for OLCI Level-2 data a set of recommended flags. Those flags are defined by an group of experts, named the Sentinel-3 Quality Working Group (S3-QWG). This group observes the data and suggests means to ESA/Eumetsat to maintain high quality. It is suggested to consider these flags when working with Sentinel-3 Level-2 data.
Detailed information: Sentinel-3 Recommended Flags

## Data Access

Sentinel-3 data can be obtained from different sources:

ESA/Copernicus Open Access hub
  The ESA/Copernicus service provides Sentinel-3 data at Level-1 and Level-2 land data. Also Level-2 synergy data is provided. Besides Sentinel-3 data, Sentinel-1 and Sentinel-2 is provided too.
  https://scihub.copernicus.eu/
EUMETSAT/Copernicus Online Data Access
  The EUMETSAT/Copernicus service provides Sentinel-3 data at Level-1 and Level-2 water data. https://view.eumetsat.int
DIAS cloud environments
  The Copernicus Data and Information Access Service (DIAS) cloud environments provide processing resources, tools and complimentary data sources at commercial conditions to further facilitate the access to Sentinel data.
  - https://creodias.eu
  - https://mundiwebservices.com
  - https://www.onda-dias.eu
  - https://sobloo.eu/index.html
NASA/OBPG Distributed Active Archive Center for satellite Ocean Biology
  The service provided by the NASA's Ocean Biology Processing Group distributes Sentinel-3 data at Level-1 and Level-2. https://oceancolor.gsfc.nasa.gov/data/overview/

## References

Sentinel Online
  Sentinel Online provides various resources about the Sentinel platforms, the data and tools to work with it.
  https://sentinel.esa.int/web/sentinel/home