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

Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010

Center for Satellite Applications and Research (STAR) Review 09 – 11 March 2010

Image:

MODIS Land Group,

NASA GSFC

March 2000

Image:

MODIS Land Group,

NASA GSFC

March 2000

Presented by

Menghua WangPresented by

Menghua Wang

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

Vicarious Calibration

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

Vicarious Calibration

22 Center for Satellite Applications and Research (STAR) Review

09 – 11 March 2010 Center for Satellite Applications and Research (STAR) Review

09 – 11 March 2010

Requirement, Science, and BenefitRequirement, 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



09 – 11 March 2010

Satellite Ocean Color Remote SensingSatellite Ocean Color Remote Sensing

10-2

10-1

400 500 600 700 800 900

Case 1, C = 0.1 mg/m3

Case 2, Sediment DominatedCase 2, Yellow Substance

Wavelength (nm)

TO

A R

efle

cta

nce

t(

)

(a)

M80 model, a(865) = 0.1

= 60o, = 45o, = 90o

0

10

20

30

40

50

400 500 600 700 800 900

Case 1, C = 0.1 mg/m3

Case-2, Sediment DominatedCase-2, Yellow Substance

Wavelength (nm)

% o

f TO

A t w

()

M80 model, a(865) = 0.1

= 60o, = 45o, = 90o

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.

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.



09 – 11 March 2010

Lunar Calibration for Characterization of Sensor Degradation

Lunar Calibration for Characterization of Sensor Degradation

SeaWiFS Looks at the Moon

Sensor Degradation

SeaWiFSSea-Viewing Wide-Field-of-view Sensor

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



09 – 11 March 2010

On-Orbit Vicarious CalibrationOn-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.



09 – 11 March 2010

Simulation Results with Vicarious Calibration

Simulation Results with Vicarious Calibration

0.01

0.1

1

400 500 600 700 800 900

a(865) = -15 a(865) = -10 a(865) = -5 a(865) = +5 a(865) = +10 a(865) = +15

( / 865)4

( / 865)3

Ra

tio a

'()

/ a

'(8

65

) (a

fte

r V

C)

Wavelength (nm)

a = 0.05

True aerosol is O99 O99 used for VC

(b)

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

a’()= a()

Inverse of Rayleigh Scattering



09 – 11 March 2010

Vicarious Calibration Requires Accurate Water-leaving Radiance Measurements

Vicarious Calibration Requires Accurate Water-leaving Radiance Measurements

Sensor-measured TOA Reflectance (or Radiance):

t = r + a + ra + twc + tw

Computed (Rayleigh)

Computed (Whitecap)

Predicted using models (Aerosols)

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

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.



09 – 11 March 2010

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

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

From D. Clark



09 – 11 March 2010

Radiance Time Series for MODIS Ocean Color Bands

Radiance Time Series for MODIS Ocean Color Bands

From D. Clark



09 – 11 March 2010

NOAA Support MOBY OperationNOAA 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.

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.



09 – 11 March 2010

Challenges and Path ForwardChallenges 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).

• 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).

Documents

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