SPOT archive imagery available through Airbus DS since the end of the mission in 2015 can now be accessed via the dedicated SWH website.
CNES has been working towards this transition since 2013, processing all of the imagery acquired by the five SPOT satellites to compile a comprehensive imagery database.
This work is not finished, but the database already contains more than 17 million scenes processed to level 1A (with radiometric corrections but not orthorectified).
Since June 2021, users can download SPOT imagery for free from an online catalogue developed by CNES.
To do so, simply create an account and agree to the terms of the ETALAB 2.0 licence. The SWH project/CNES must be credited in all downloaded images used.
More planned upgrades to further facilitate access and uptake of SPOT data include the ability to upload a file covering your specific area of interest. This feature should be available online by the end of this year. A free service for processing imagery to level 1C (orthorectified and values converted to top-of-atmosphere (TOA) reflectance) is also planned. A related website is already online for orthorectifying level 1A images.
Images are resampled in a map projection (currently UTM) at constant elevation using the simplified level 1A geometric model, without geocoding or use of a DEM. They are in digital numbers (DN) and 8-bit encoded.
This offers several advantages:
- product geometry is readily usable
- pixels are constant size (to allow for panoramic distortion)
- processing is extremely fast (2 to 4 seconds depending on product resolution)
The one drawback is that product geolocation performance is the same as for level 1A (about 500 m RMS for SPOT 1-2-3, 200 m for SPOT 4 and 50 m for SPOT5), a degree of error that basically equates to a constant displacement of the entire image and can be allowed for simply through a translation.