Where can I download freely available images for night from for South Asian region?
There are DMSP-OLS Nighttime Lights Time Series data that can be download from NOAA website. The files are:
Cloud-free composites made using all the available archived DMSP-OLS smooth resolution data for calendar years. In cases where two satellites were collecting data - two composites were produced. The products are 30 arc second grids, spanning -180 to 180 degrees longitude and -65 to 75 degrees latitude.
Which means it covers South Asian region.
There is another question addressing this topic, maybe it can give you som extra information.
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