4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

Effect of Ocean Surface Roughness onRadiative Transfer in Atmosphere and

Ocean

Zhonghai Jin1, Thomas Charlock2, Ken Rutledge1

1 Analytical Services & Materials, Inc., Hampton,VA 23666

2 Atmospheric Sciences Division, NASA LangleyResearch Center, Hampton, VA 23681

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

Monte Carlo or ray tracing technique is usually used toconsider the ocean surface roughness for radiativetransfer, which is relatively easy to be implemented incode but is computationally expensive.

We use an analytical technique (the discrete-ordinatemethod) for this problem. Analytical solution is moreefficient and has no statistical fluctuation as in MonteCarlo method, but is hard to be implemented in code.

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

The analytical solution has been implemented into theCoupled DIScrete-Ordinate Radiative Transfer (CDISORT)code. Using CDISORT as the radiative transfer solver, aCoupled Ocean-Atmosphere Radiative Transfer (COART)has been developed.

Because CDISORT included the refractive index and nowincludes the surface roughness parameters, COART treatsthe ocean strata just as additional atmospheric layers withdifferent optical properties.

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

COART is online at http://www-cave.larc.nasa.gov/cave/

Find it by searching “COART model” or “Atmopshere-ocean radiative transfer model”.

COART can calculate the spectral and broadband radiances,including the water-leaving radiance, and fluxes at anylevels in atmosphere and ocean, but we will show only someresults closely related to ocean surface roughness here.

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

Figure 1. Modelsimulated upwellingradiance field at thetop of atmosphere(TOA) and thedownwelling radiancefield at depths of 10 mand 50 m in the oceanfor wind speeds of 3, 6and 10 w/s and forthree wavelengthspectra, respectively.

SZA = 40o

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

Figure 2. Effects ofsurface roughness onradiancedistributions inprincipal planearound the reflectedsolar beam directionin atmosphere andthe refracted solardirection in ocean.

SZA = 40o

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

Figure 3. Comparison of modeled and measuredradiances as a function of sun-glint angle.

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

Figure 4. Modeledsimulated upwellingirradiance inatmosphere anddownwellingirradiance in theocean for differentwind speeds anddifferentwavelengths.

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

Figure 5. Effects of wind speed on ocean surface albedo. Theleft panel shows the modeled and measured surface albedo

in three days. The right panel shows the corresponding windspeeds observed in these days. Different colors are for

different days.

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

Figure 6. Effects ofwave shadowing andmultiple scatteringbetween surface facetson the calculatedsurface albedo.

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

¬ Ocean surface roughness effects, including wave shadowingand multiple scattering between surface facets, are treatedanalytically and accurately in radiative transfer solutions.

¬ Model simulations show that the ocean surface roughness hassignificant effects on the upward radiation field in atmosphereand downward radiation in ocean, particularly, the sunglintpattern and ocean surface albedo.

¬ As surface roughness or wind increases, the sunglint regionbroadens and the surface albedo decreases, but thetransmission to ocean increases.

Summary

4th CERES-II Science Team MeetingRadisson, Hampton, VA.

November 1-3, 2005

¬ The transmitted radiance field in ocean is highly anisotropicand this anisotropic feature rapidly decreases as surface windincreases and as depth in ocean increases.

¬ Down deeper into ocean, optical properties of ocean becomemore important than surface roughness to radiation field.

¬ The effects of surface roughness on radiation also greatlydepend on wavelength and solar elevation. They aresignificantly smaller at high sun conditions for all spectrum.

¬ Model results are consistent with measurements.