Visualizing the vegetation dynamics in Africa

The Global Imagery Browse Services is an API provided by the NASA to access its vast collection of Earth Observation products.

It’s convenient to use the Worldview online data browser to get the right URL template. Just click on « Take a snapshot » and copy the URL. For example the following URL allows you to download a jpeg picture of the Terra MODIS NDVI in December 2002 over Africa:

By looping on the « TIME » parameter (in a bash script using wget) you can get every monthly products from 2001 to 2020, and make this animation ( using ffmpeg). The « & » symbol in the end of the line sends the download requests in parallel (don’t abuse of it).

for yy in $(seq 2001 2020)
do
  for mm in 01 02 03 04 05 06 07 08 09 10 11 12
  do
   wget "https://wvs.earthdata.nasa.gov/api/v1/snapshot?REQUEST=GetSnapshot&BBOX=-36.03751831054688,-18.663024902343757,37.77621459960939,52.163305664062506&CRS=EPSG:4326&LAYERS=Coastlines,MODIS_Terra_L3_NDVI_Monthly&WRAP=x,day&FORMAT=image/jpeg&WIDTH=806&HEIGHT=840&TIME=$yy-$mm-01T00:00:00Z" -O $yy-$mm.jpg &
  done
done

You can also download the images as Geotiff if you wish to combine them with other geospatial data.

Each layer comes with a specific colormap that is consistent with the product. In addition you can download a stack of multiple layers with different opacities, for example you can overlay the MODIS « fire » layer on the « NDVI » layer.

Note: this article was updated on 25 Jan 2021.