Swot Data Products

Data Products for Hydrology

Four main products have been defined. The rawest is in NetCDF format, while the other three are in shapefile format, compatible with GISs. River- and lake-specific products are linked to a priori databases, which will be updated during the mission.

"River" products

Each river over 30 m wide is defined in an a priori database, either as a line along the centre of the river divided into sections about 10 km long, or as nodes every 200 m along this line. 

River products are provided according to these two types of breakdown, as defined in the a priori database: for the "node" product, with mean values around each node for parameters such as width, height, flooded area, etc., and for the "section" product the mean height, mean slope, mean flow, etc. on each of these river sections.

These products are provided for each satellite pass.

The "section" product is also provided by cycle, in which case the values of the variables are provided on each of the different passes that measured all or part of the section of the river in question during an entire satellite cycle (21 days). 

See a movie illustrating these products

Definition of river nodes
Definition of river nodes
Definition of a river section
Definition of a river section

"Lake" products

Water surfaces that are not known rivers, and that are more than one hectare in size, are treated as "lakes". 

The product for each individual satellite pass gives information (height, surface area, contour, etc.) for each observation of these surfaces. 

For each object that can be linked to an element of the a priori lakes database, the identification information is added.

The product for each cycle includes a median contour, and the average height of the lakes for passes when they were seen in their entirety (observations of only part of the lake are not taken into account). Other more complex scenarios (views of different parts of the lake at each passage) will be taken into account.

See a movie illustrating these products

Illustration of the definition of the contours of a lake (Figure courtesy of Y. Sheng)
Illustration of the definition of the contours of a lake (Figure courtesy of Y. Sheng)

"Raster" products

A "raster" product (see the example of the Po above) will be systematically generated from the "pixel cloud" product. It will be in NetCDF 2D format, will cover four point-cloud tiles (the 2 swaths and 120km along the ground track) and will come in two resolutions: 100m and 250m. The points of the pixel cloud will be plotted on a regular grid according to a Universal Transverse Mercator (UTM) projection. This will be a one-per-pass product.

It can also be generated on demand (via the data dissemination portal, TBC): 

  • format: NetCDF, GeoTiff, etc.,
  • variables,
  • resolution (>100m) and user-defined area, with a limit on the volume of the data to be downloaded.
Swot data simulated for a river: example of the Po (Italy)
Swot data simulated for a river: example of the Po (Italy)
Pixel cloud product on one of the swaths
Pixel cloud product on one of the swaths

"Pixel cloud" product 

This is the rawest product for land surfaces. A file, in NetCDF format, covers a tile, which corresponds to a swath on one of the two sides (left or right) over 60 km along the satellite's ground track.

The product provides longitude, latitude, height, pixel size and corrections for each point classified as water, for points on a buffer zone around these water zones as well as on systematically included areas (defined according to an a priori mask).

This product is generated for each pass of the satellite. 

(Left: raw pixel cloud – Right: improved geolocation)

Data Products for Oceanography

Oceanographic data over the open ocean are "low resolution", pre-processed on board.

The variables provided in the data and formats will be quite similar to the Geophysical Data Records existing today in conventional altimetry, but on swaths (so in two dimensions instead of along the track).

Several variants of these products will be distributed, in half orbits (tracks), at 2 x 2 km resolution, every 2 km, on a grid following the ground track:

  • SSH/SSHA "basic" products
  • wind / waves / sigma0 "Basic" product 
  • Expert products, with the information of the SSH/SSHA commodities, but also all the corrections, auxiliary data, etc. necessary for their calculation (note some additional corrections compared to conventional altimetry, in particular errors induced by the roll angle, and internal tides)

These three data sets being provided

  • on the actual ground track (which may vary by +/- 1 km from the theoretical orbit)
  • and also in variants projected on the theoretical ground track (therefore always stable from one cycle to the next).
  • A final expert dataset "SSH and Sigma0 Power and Variance", with a native resolution of one pixel of 500 m x 500 m every 250 m, will also be available.