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Marine Optical Buoy (MOBY): Support for Ocean Color Sensor Vicarious Calibration. Presented by Menghua Wang. Requirement, Science, and Benefit. Requirement/Objective Ecosystems Protect, restore and manage the use of coastal and ocean resources through ecosystem-based management

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marine optical buoy moby support for ocean color sensor vicarious calibration

Marine Optical Buoy (MOBY): Support for Ocean Color Sensor Vicarious Calibration

Presented by

Menghua Wang

requirement science and benefit
Requirement, Science, and Benefit

Requirement/Objective

  • Ecosystems
    • Protect, restore and manage the use of coastal and ocean resources through ecosystem-based management
      • Healthy and productive coastal and marine ecosystems that benefit society
      • Advancing understanding of ecosystems to improve resource management
      • A well informed public that acts as a steward of coastal and marine ecosystems
  • Weather and Water
    • Serve society’s needs for weather and water information
      • Better, quicker, and more valuable weather and water information to support improved decisions
      • Increase lead time and accuracy for weather and water warnings and forecasts
      • Improve predictability of the onset, duration, and impact of hazardous and high-impact severe weather and water events

Science

  • How to provide accurate water optical, biological, and biogeochemical property data in coastal and inland regions from satellite measurements?

Benefit

  • Protect and monitor our ocean resource
  • Improve water resources forecasting capabilities
  • Protect and monitor water resources
  • Understand the effect of environmental factors on human health and well-being
satellite ocean color remote sensing
Satellite Ocean Color Remote Sensing
  • Ocean Color Remote Sensing: Derive the ocean water-leaving radiance spectra by accurately removing the atmospheric and surface effects.
  • Ocean properties can then be derived from the ocean water-leaving radiance spectra.
  • At satellite altitude usually ~90% of sensor-measured signal over ocean comes from the atmosphere & surface
    • It is crucial to have accurate atmospheric correction and sensor calibration.
    • 0.5% error in the TOA radiance corresponds to possible of ~5% in the derived ocean water-leaving radiance.
    • We need ~0.1% sensor calibration accuracy.
    • On-orbit vicarious calibration is necessary.
lunar calibration for characterization of sensor degradation
Lunar Calibration for Characterization of Sensor Degradation

SeaWiFSSea-ViewingWide-Field-of-viewSensor

SeaWiFS Looks at the Moon

Sensor Degradation

From http://oceancolor.gsfc.nasa.gov

on orbit vicarious calibration
On-Orbit Vicarious Calibration
  • For ocean color remote sensing, post-launch vicarious calibration is necessary for visible bands.
  • Vicarious Calibration:Calibration of whole system: Sensor + Algorithms
    • Account for (by direct measurement or prediction) all of the components of the TOA radiance and
    • Compare the results with the sensor-measured radiance.
  • Sensor-measured reflectance:t(meas) = [1 + a()] t a()--Calibration error
  • After vicarious calibration: t(V) = [1 + a’()] t a’()--Calibration error
  • It is found (Wang and Gordon, 2002) that a’() depends only on the longest wavelength of a()(e.g., 865 nm, a()).
  • Thus, a’() for the visible bands can be significantly reduced after on-orbit vicarious calibration.

Wang, M. and H. R. Gordon, “Calibration of ocean color scanners: How much error is acceptable in the near-infrared,” Remote Sens. Environ., 82, 497-504, 2002.

simulation results with vicarious calibration
Simulation Results with Vicarious Calibration

a’()= a()

Inverse of Rayleigh Scattering

After VC, calibration errors a’() for the visible bands are significantly reduced.

vicarious calibration requires accurate water leaving radiance measurements
Vicarious Calibration Requires Accurate Water-leaving Radiance Measurements

Computed (Rayleigh)

Predicted using models (Aerosols)

Computed (Whitecap)

Measured at vicarious calibration site, e.g., MOBY

Sensor-measured TOA Reflectance (or Radiance):

t = r + a + ra + twc + tw

  • It has been demonstrated that VC is necessary for producing accurate satellite ocean color products.
  • Post-launch vicarious calibration has been carried out for SeaWiFS and MODIS, and will also be carried out for the MERIS.
  • We are currently working on implementing the vicarious calibration method for routinely deriving the gains for the MODIS-Aqua data products.
noaa support moby operation
NOAA Support MOBY Operation
  • MOBY data have been used for vicarious calibration of ocean color satellite sensors SeaWiFS and MODIS, as well as in support for calibration for various other international ocean color sensors.
  • SeaWiFS and MODIS-Aqua have been producing high quality global open ocean color products.
  • MOBY data will be needed in support for the on-orbit vicarious calibration for NPOESS/VIIRS for generating global ocean color products.
  • NOAA will need to build End-to-End ocean color data processing capability, including sensor calibration capability using MOBY data.
challenges and path forward
Challenges and Path Forward
  • Science challenges
    • Providing accurate and consistent in situ data measurements for calibration and validation of ocean color products.
  • Next steps
    • Develop next generation instrument (new MOBY) for satellite sensors calibration.
  • Transition Path
    • Development of techniques for routine calibration applications for ocean color satellite sensors (both US and international).
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