Basics of satellite remote sensing: 3) How do I access satellite data?

If you think finding, downloading, and analyzing satellite data is confusing, you’re not alone. The different satellites, sensors, and websites to retrieve data is overwhelming and I think somewhat user prohibiting. A quick Google search might lead to what you’re looking for, but in my experience it’s led to even more confusion and questions. Therefore, I would like to devote this blog to explain how to access the appropriate type of satellite imagery. Since my focus is on ocean color satellites, it might be best to inquire from someone else the best satellite data for terrestrial or meteorological uses.

Before searching for satellite imagery, there are a few questions you should answer:

  • What are trying to get satellite imagery of?
    • Do you want global coverage? Or are you looking at a particular estuary or lake? The spatial resolution (i.e. the size of the pixels) will matter.
  • How much time do you have?
    • Do you want to get quick image in an hour or less? Do you want to bulk download imagery for multiple dates? If you’re only worried about visualizing imagery, downloading big files might not be necessary.
  • What type of data do you want?
    • Do you simply want to view satellite images of a particular area on your computer? Do you want to download the matrix of values as a netCDF file? Or do you want to download a GeoTIFF to pull into GIS? This will determine what website or program to use. There are some websites solely for downloading, some that are user-friendly for visualizing, and some programs that have advanced capabilities for analyzing and manipulating.
  • Do you care about satellite processing parameters?
    • Will the standard satellite processing parameters (e.g. atmospheric correction, chlorophyll algorithms) be appropriate for your work? Or do you want to process the imagery on your own? This will determine what level satellite imagery you get. Level 0 or 1 is usually top-of-atmosphere (TOA) radiance while Level 2, 3, and sometimes 4 is bottom-of-atmosphere (BOA) radiance, meaning satellite imagery has been processed to eliminate the effects of atmosphere on the water/land leaving signal. Sometimes, standard satellite chlorophyll algorithms lead to erroneous results in some water types which is why researchers process imagery using other bio-optical algorithms.



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