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A Brief Introduction to (Ocean Color) Remote Sensing of Water Quality

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A Brief Introduction to (Ocean Color) Remote Sensing of Water Quality A brief introduction to (ocean color) remote sensing of water quality Jeremy Werdell Joel Scott, Ryan Vandermuelen NASA Goddard Space Flight Center Ocean Ecology Laboratory NASA Water Quality Workshop 27 September 2017 Why NASA? Why satellites? http://www.chesapeakebay.net routine data collection since 1984 12-16 cruises / year 49 stations 19 hydrographic measurements algal biomass Chesapeake Bay Program water clarity dissolved oxygen 1-day of MODIS-Aqua satellites complement in situ sampling with routine, synoptic, & consistent views of our critical marine ecosystems NASA Water Quality Workshop [email protected] 2 What is “ocean color”? clear water sediment-rich water ) l ( s r R Water Reflectance Water Spectral Wavelength (l) color the spectral distribution of reflected sunlight can be used to infer the contents of the water NASA Water Quality Workshop [email protected] 3 Measurements of ocean color are based on electromagnetic energy emitted by sunlight, transmitted through atmosphere, and reflected by Earth’s surface. Water-leaving Radiance, Lw AIR SEA SCATTERING (bb) Organic Matter There are two Detritus possible things that Phytoplankton can happen to a photon in water ABSORPTION (a) NASA Water Quality Workshop [email protected] 4 400 500 600 700 400 500 600 700 400 500 600 700 400 500 600 700 400 500 600 700 NASA Water Quality Workshop [email protected] 5 chlorophyll-a (algal biomass) Ocean color data products ) 3 - diffuse light attenuation dissolved organic matter a (mg m (water clarity, turbidity) absorption (runoff) - chlorophyll ratio of blue:green radiances and, many others, including: phytoplankton community composition (including HABs) particle size distributions (water composition) particulate (in)organic carbon (productivity) euphotic depth (visibility, water clarity) particle backscattering water temperature (MODIS, VIIRS) red light reflectance (sediment load) (sediment load) NASA Water Quality Workshop [email protected] 6 Steps for deriving ocean color data products from space the satellite views the spectral light SATELLITE field at the top-of-the-atmosphere TOP-OF-THE-ATMOSPHERE 1. remove atmosphere from total 3. spatially / temporally signal to derive estimate of light bin and remap the field emanating from sea surface satellite observations (remote sensing reflectance, Lw) SEA SURFACE the water signal is often less than 10% of the total signal measured by the satellite 2. relate spectral Lw to a chlorophyll-a concentration (or PHYTOPLANKTON geophysical product of interest) NASA Water Quality Workshop [email protected] 7 Different instruments & missions offer different capabilities Landsat 8 OLI, 26 Oct 2016, Queensland, Australia different algal groups (spectral bands) image artifacts dark ocean compared to bright targets atmospheric correction (spectral bands + instrument performance) temporal repeatability ground sample contamination distances by Sun glint NASA Water Quality Workshop [email protected] 8 Heritage & future missions NASA Water Quality Workshop [email protected] 9 Applications for water quality monitoring NASA Water Quality Workshop [email protected] 10 Towards demystifying the use of satellite ocean color data https://oceancolor.gsfc.nasa.gov NASA Water Quality Workshop [email protected] 11 Further demystifying the use of satellite ocean color data seadas.gsfc.nasa.gov https:// NASA Water Quality Workshop [email protected] 12 Thank you NASA Water Quality Workshop [email protected] 13.
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