Marine optical buoy moby support for ocean color sensor vicarious calibration
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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

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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

      • 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

  • 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

SeaWiFSSea-ViewingWide-Field-of-viewSensor

SeaWiFS Looks at the Moon

Sensor Degradation

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


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

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

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.


Marine Optical Buoy (MOBY)-VC Facility for Ocean Color Sensor

From D. Clark


Radiance Time Series for MODIS Ocean Color Bands

From D. Clark


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

  • 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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