Ocean optics research done “ in situ ” (from research vessels, small boats, or on docks and piers) supports research that uses satellite data. In situ optical measurements provide a way to: 1) calibrate satellite sensors when they are just beginning to collect data, 2) develop algorithms to derive products or variables like chlorophyll-a concentration, and 3) validate data products derived from satellites. Using satellite data, researchers estimate things like particle size, carbon, water quality, water clarity, and bottom type based on the color profile as seen by satellite; all of these estimations (aka models) must be validated by comparing them to optical measurements made in situ. In situ data are often available from publicly accessible data libraries like the SeaBASS data archive.