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

1. Marine Optical Buoy (MOBY): Support for Ocean Color Sensor Vicarious Calibration Presented by Menghua Wang

2. 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

3. 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.

4. 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

5. 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.

6. Simulation Results with Vicarious Calibration a’()= a() Inverse of Rayleigh Scattering After VC, calibration errors a’() for the visible bands are significantly reduced.

7. 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.

8. Marine Optical Buoy (MOBY)-VC Facility for Ocean Color Sensor From D. Clark

9. Radiance Time Series for MODIS Ocean Color Bands From D. Clark

10. 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.

11. 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).