• Barker, H. W., 1994: Solar radiative transfer for wind-sheared cumulus cloud fields. J. Atmos. Sci.,51, 1141–1156.

  • ——, and J. A. Davies, 1992: Solar radiative fluxes for stochastic, scale-invariant broken cloud fields. J. Atmos. Sci.,49, 1115–1126.

  • Bohren, C. F., and D. R. Huffman, 1983: Absorption and Scattering of Light by Small Particles. John Wiley, 530 pp.

  • Bréon, F.-M., 1992: Reflectance of broken cloud fields: Simulation and parameterization. J. Atmos. Sci.,49, 1221–1232.

  • Busygin, V. P., N. A. Yevstratov, and Y. M. Feigel’son, 1973: Optical properties of cumulus clouds, and radiant fluxes for cumulus cloud cover (English translation). Izv. Acad. Sci. USSR, Atmos. Oceanic Phys.,9, 1142–1151.

  • Cahalan, R. F., W. Ridgway, W. J. Wiscombe, T. L. Bell, and J. B. Snider, 1994: The albedo of fractal stratocumulus clouds. J. Atmos. Sci.,51, 2434–2455.

  • Coakley, J. A., Jr., 1991: Reflectivities of uniform and broken layered clouds. Tellus,43B, 420–433.

  • ——, and F. P. Bretherton, 1982: Cloud cover from high-resolution scanner data: Detecting and allowing for partially filled fields of view. J. Geophys. Res.,87, 4917–4932.

  • ——, and D. G. Baldwin, 1984: Toward the objective analysis of clouds from satellite imagery data. J. Climate Appl. Meteor.,23, 721–730.

  • ——, and R. Davies, 1986: The effect of cloud sides on reflected solar radiation as deduced from satellite observations. J. Atmos. Sci.,43, 1025–1035.

  • Davies, R., 1978: The effect of finite geometry on the three-dimensional transfer of solar irradiance in clouds. J. Atmos. Sci.,35, 1712–1725.

  • ——, 1984: Reflected solar radiances from broken cloud scenes and the interpretation of scanner measurements. J. Geophys. Res.,89, 1259–1266.

  • ——, 1994: Spatial autocorrelation of radiation measured by the Earth Radiation Budget Experiment: Scene inhomogeneity and reciprocity violation. J. Geophys. Res.,99, 20879–20887.

  • Deirmendjian, D., 1969: Electromagnetic Scattering on Spherical Polydispersions. Elsevier, 290 pp.

  • Di Girolamo, L., and R. Davies, 1997: Cloud fraction errors caused by finite resolution measurements. J. Geophys. Res.,102, 1739–1756.

  • Frulla, L. A., J. A. Milovich, and D. A. Gagliardini, 1995: Illumination and observation geometry for NOAA-AVHRR images. Int. J. Remote Sens.,16, 2233–2253.

  • Hale, G. M., and M. R. Querry, 1973: Optical constants of water inthe 200-nm to 200-μm wavelength region. Appl. Opt.,12, 555–563.

  • Kidwell, K. B., 1994: NOAA polar orbiter data users guide. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Environmental Satellite, Data and Information Service, National Climatic Data Center, Satellite Data Services Division, 250 pp. [Available from Federal Office Building ;ns3, Room G-233, Washington, DC 20233.].

  • Klein, S. A., and D. L. Hartmann, 1993: The seasonal cycle of low stratiform clouds. J. Climate,6, 1587–1606.

  • Kneizys, F. X., E. P. Shettle, L. W. Abreu, J. H. Chetwynd Jr., G. P. Anderson, W. O. Gallery, J. E. A. Selby, and S. A. Clough, 1988:Users guide to LOWTRAN 7. Rep. AFGL–TR–88–0177, 137 pp. [Available from Phillips Laboratory, Geophysics Directorate, PL/GPOS, 29 Randolph Rd., Hanscom AFB, MA 01731-3010.].

  • Kobayashi, T., 1993: Effects due to cloud geometry on biases in the albedo derived from radiance measurements. J. Climate,6, 120–128.

  • Loeb, N. G., 1997: In-flight calibration of NOAA AVHRR visible and near-IR bands over Greenland and Antarctica. Int. J. Remote Sens.,18, 477–490.

  • ——, and R. Davies, 1996: Observational evidence of plane parallel model biases: Apparent dependence of cloud optical depth on solar zenith angle. J. Geophys. Res.,101, 1621–1634.

  • ——, and ——, 1997: Angular dependence of observed reflectances:A comparison with plane parallel theory. J. Geophys. Res.,102, 6865–6881.

  • ——, T. Várnai, and R. Davies, 1997: The effect of cloud inhomogeneities on the solar zenith angle dependence of nadir reflectance. J. Geophys. Res.,102, 9387–9395.

  • McKee, T. B., and S. K. Cox, 1974: Scattering of visible radiation by finite clouds. J. Atmos. Sci.,31, 1885–1892.

  • Minnis, P., 1989: Viewing zenith angle dependence of cloudiness determined from coincident GOES East and GOES West data. J. Geophys. Res.,94, 2303–2320.

  • ——, and E. F. Harrison, 1984: Diurnal variability of regional cloud and clear-sky radiative parameters derived from GOES data. Part II: November 1978 cloud distributions. J. Climate Appl. Meteor.,23, 1012–1051.

  • ——, P. W. Heck, D. F. Young, C. W. Fairall, and J. B. Snider, 1992:Stratocumulus cloud properties derived from simultaneous satellite and island-based instrumentation during FIRE. J. Appl. Meteor.,31, 317–339.

  • Oreopoulos, L., and R. Davies, 1998: Plane parallel albedo biases from satellite observations. Part I: Dependence on resolution and other factors. J. Climate, in press.

  • Rossow, W. B., 1989: Measuring cloud properties from space: A review. J. Climate,2, 201–213.

  • ——, L. C. Garder, and A. A. Lacis, 1989: Global, seasonal cloud variations from satellite radiance measurements. Part I: Sensitivity of analysis. J. Climate,2, 419–458.

  • Shenk, W. F., and V. V. Salomonson, 1972: A simulation study exploring the effects of sensor spatial resolution on estimates of cloud cover from satellites. J. Appl. Meteor.,11, 214–220.

  • Singh, S. M., and A. P. Cracknell, 1986: The atmospheric effects for SPOT using AVHRR channel-1 data. Int. J. Remote Sens.,7, 361–377.

  • Sprent, P., 1989: Applied Nonparametric Statistical Methods. Chapman and Hall Limited, 259 pp.

  • Stamnes, K., S.-C. Tsay, W. Wiscombe, and K. Jayaweera, 1988: Numerically stable algorithm for discrete-ordinate-method radiative transfer in multiple scattering and emitting layered media. Appl. Opt.,24, 2502–2509.

  • Stuhlmann, R., P. Minnis, and G. L. Smith, 1985: Cloud bidirectional reflectance functions: A comparison of experimental and theoretical results. Appl. Opt.,24, 396–401.

  • Taylor, V. R., and L. L. Stowe, 1983: Reflectance characteristics of uniform earth and cloud surfaces derived from Nimbus 7 ERB. J. Geophys. Res.,89, 4987–4996.

  • Várnai, T., 1996: Reflection of solar radiation by inhomogeneousclouds. Ph.D. thesis, McGill University, 146 pp. [Available from McGill University, 805 Sherbrooke Street West, Montreal, PQ, H3A 2K6 Canada.].

  • Warren, S. G., C. J. Hahn, J. London, R. M. Chervin, and R. L. Jenne, 1988: Global distribution of total cloud cover and cloud type amounts over the ocean. NCAR Tech. Note TN-317+STR, Boulder, CO, 42 pp. plus 170 maps.

  • Wendling, P., 1977: Albedo and reflected radiance of horizontally inhomogeneous clouds. J. Atmos. Sci.,34, 642–650.

  • Wielicki, B. A., and R. M. Welch, 1986: Cumulus cloud properties derived using Landsat satellite data. J. Climate Appl. Meteor.,25, 261–276.

  • ——, and L. Parker, 1992: On the determination of cloud cover from satellite sensors: The effect of sensor spatial resolution. J. Geophys. Res.,97, 12799–12823.

  • Ye, Q., and J. A. Coakley Jr., 1996: Biases in earth radiation budget observations. Part 2: Consistent scene identification and anisotropic factors. J. Geophys. Res.,101, 21253–21263.

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Inference of Marine Stratus Cloud Optical Depths from Satellite Measurements: Does 1D Theory Apply?

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  • 1 College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon
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Abstract

The validity of plane-parallel (1D) radiative transfer theory for cloudy atmospheres is examined by directly comparing calculated and observed visible reflectances for one month of Global Area Coverage Advanced Very High Resolution Radiometer satellite observations of marine stratus cloud layers off the coasts of California, Peru, and Angola. Marine stratus are an excellent testbed, as they arguably are the closest to plane-parallel found in nature. Optical depths in a 1D radiative transfer model are adjusted so that 1D model reflectances match those observed at nadir on a pixel-by-pixel basis. The 1D cloud optical depth distributions are then used in the plane-parallel model to generate reflectance distributions for different sun–earth–satellite viewing geometries. These reflectance distributions are directly compared with the observations. Separate analyses are performed for overcast and broken cloud layers as identified by the spatial coherence method.

When 1D reflectances are directly compared with observations at different view angles, relative differences are generally small (≲10%) in the backscattering direction for solar zenith angles ≲60° and show no systematic view angle dependence. In contrast, 1D reflectances increase much more rapidly with view angle than the observed reflectances in the forward-scattering direction. Relative differences in the forward-scattering direction are ≈2–3 times larger than in the backscattering direction. At solar zenith angles ≳60°, the 1D model underestimates observed reflectances at nadir by 20%–30% and overestimates reflectances at the most oblique view angles in the forward scattering direction by 15%–20%. Consequently, when inferred on a pixel-by-pixel basis, nadir-derived cloud optical depths show a systematic increase with solar zenith angle, both for overcast and broken cloud layers, and cloud optical depths decrease with view angle in the forward scattering direction. Interestingly, in the case of broken marine stratocumulus, the common practice of assuming that pixels are overcast when they are not mitigates this bias to some extent, thereby confounding its detection. But even for broken clouds, the bias remains.

Because of the nonlinear dependence of cloud albedo on cloud optical depth, errors in cloud optical depth lead to large errors in cloud albedo—and therefore energy budget calculations—regardless of whether cloud layers are overcast or broken. These findings suggest that as a minimum requirement, direct application of the plane-parallel model approximation should be restricted to moderate–high sun elevations and to view angles in the backscattering direction. Based on Monte Carlo simulations, the likely reason for the discrepancies between observed radiances and radiances calculated on the basis of 1D theory is because real clouds have inhomogeneous (i.e., bumpy) tops.

* Current affiliation: Center for Atmospheric Sciences, Hampton University, Hampton, Virginia.

Corresponding author address: Dr. Norman G. Loeb, Mail Stop 420, NASA Langley Research Center, Hampton, VA 23681.

Abstract

The validity of plane-parallel (1D) radiative transfer theory for cloudy atmospheres is examined by directly comparing calculated and observed visible reflectances for one month of Global Area Coverage Advanced Very High Resolution Radiometer satellite observations of marine stratus cloud layers off the coasts of California, Peru, and Angola. Marine stratus are an excellent testbed, as they arguably are the closest to plane-parallel found in nature. Optical depths in a 1D radiative transfer model are adjusted so that 1D model reflectances match those observed at nadir on a pixel-by-pixel basis. The 1D cloud optical depth distributions are then used in the plane-parallel model to generate reflectance distributions for different sun–earth–satellite viewing geometries. These reflectance distributions are directly compared with the observations. Separate analyses are performed for overcast and broken cloud layers as identified by the spatial coherence method.

When 1D reflectances are directly compared with observations at different view angles, relative differences are generally small (≲10%) in the backscattering direction for solar zenith angles ≲60° and show no systematic view angle dependence. In contrast, 1D reflectances increase much more rapidly with view angle than the observed reflectances in the forward-scattering direction. Relative differences in the forward-scattering direction are ≈2–3 times larger than in the backscattering direction. At solar zenith angles ≳60°, the 1D model underestimates observed reflectances at nadir by 20%–30% and overestimates reflectances at the most oblique view angles in the forward scattering direction by 15%–20%. Consequently, when inferred on a pixel-by-pixel basis, nadir-derived cloud optical depths show a systematic increase with solar zenith angle, both for overcast and broken cloud layers, and cloud optical depths decrease with view angle in the forward scattering direction. Interestingly, in the case of broken marine stratocumulus, the common practice of assuming that pixels are overcast when they are not mitigates this bias to some extent, thereby confounding its detection. But even for broken clouds, the bias remains.

Because of the nonlinear dependence of cloud albedo on cloud optical depth, errors in cloud optical depth lead to large errors in cloud albedo—and therefore energy budget calculations—regardless of whether cloud layers are overcast or broken. These findings suggest that as a minimum requirement, direct application of the plane-parallel model approximation should be restricted to moderate–high sun elevations and to view angles in the backscattering direction. Based on Monte Carlo simulations, the likely reason for the discrepancies between observed radiances and radiances calculated on the basis of 1D theory is because real clouds have inhomogeneous (i.e., bumpy) tops.

* Current affiliation: Center for Atmospheric Sciences, Hampton University, Hampton, Virginia.

Corresponding author address: Dr. Norman G. Loeb, Mail Stop 420, NASA Langley Research Center, Hampton, VA 23681.

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