Free satellite images can be very useful. But you must take care. Giving away satellite images can happen for a number of political and economical reasons. His definition of free is:
Without a subjective filter when.
Without a subjective filter where.
There are two basic types of satellites. Geostationary weather satellites. These satellites always take pictures of the same area. A big advantage is that they can take images with high frequency as they’re always above the same area. USA satellites have quite some free image data. Japan fewer and with limitations. EU not.
The second type is that of the earth observation satellites. These fly over the north and south pole and they are synchronized with the sun. One “round” takes about 1.5 hours. This way they cover most/all of the earth every day.
VIIRS. Data available at https://worldview.earthdata.nasa.gov
MODIS. Nasa. The first really open satellite data. With a 15 year archive. This is the most often used one. (Also available at above url).
Landsat. US geological service. The most well-known one. This one has the greatest amount of data. It was not always free data. And the polar areas and the seas are missing.
They tried for 20 years to make it into a commercial venture, which didn’t work out. So it came back into governmental hands. Since 2008 all data is open.
Almost live images: https://www.mapbox.com/bites/00145
EU satellites? Traditionally there is no open data. But the landsat open data success prompted a re-thinking. So now there is the COPERNICUS program.
Sentinel tries to copy the landsat success. It now produces the most complete data set. But: it focuses on Europe, Africa and Greenland. There also is no data from before oktober 2016.
Data is available at https://scihub.copernicus.eu/
My name is Reinout van Rees and I work a lot with Python (programming language) and Django (website framework). I live in The Netherlands and I'm happily married to Annie van Rees-Kooiman.
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