### Abstract

Monte Carlo reflectance simulations of three tropical cumulus congestus clouds reconstructed from Multiangle Imaging Spectroradiometer (MISR) data are compared to the domain-averaged MISR reflectance measurements. The goal of the comparison is to evaluate the nadir-view pixel cloud optical depth retrievals derived using plane-parallel radiative transfer theory, and the assumptions for vertically distributing the optical depth. Cloud heights are operationally retrieved using a stereo-imaging algorithm. The cloud heights and optical depths are at a 275 m spatial resolution, and for most simulations a vertical resolution of 250 m is applied. Five different but common three-dimensional cloud representations are assessed, using (1) a column vertical-mean volume extinction coefficient (β) value (the reference case), (2) a volume extinction coefficient proportional to the two-thirds power of height (the adiabatic assumption), (3) the adiabatic assumption at a 25 m vertical resolution, (4) a vertical-mean β retrieved from reflectances averaged over a (2.2 km)^{2} area, and (5) a vertical-mean β retrieved using off-nadir reflectances. An asymmetry about nadir in the observed reflectance means and skewnesses is not reproduced by any Monte Carlo simulation. The lack of symmetry can be related to differing proportions of unobscured sunlit and shadowed cloudy areas within the different views, even for these cases with viewing angles close to the perpendicular plane. The Monte Carlo simulations do not appear to capture the observed fraction of unobscured sunlit and shadowed cloudy areas, suggesting that radiatively significant cloud variability is occurring at scales smaller than the height field resolution of ±550 m. Results from the Monte Carlo simulation done at a higher vertical resolution are consistent with this. The cases examined also contain a nadir maximum in the observed reflectance skewnesses and a relative maximum for the observed nadir reflectances, attributed to the solar illumination of some optically thick cloud surfaces and to specular reflection pervading through the optically thin cloudy regions. This contrasts with previous modeling results that assume a Lambertian surface.

Original language | English (US) |
---|---|

Article number | 4626 |

Journal | Journal of Geophysical Research C: Oceans |

Volume | 108 |

Issue number | 20 |

DOIs | |

State | Published - Oct 27 2003 |

Externally published | Yes |

### Fingerprint

### Keywords

- 3-D radiative transfer
- Cumulus congestus
- MISR

### ASJC Scopus subject areas

- Geochemistry and Petrology
- Geophysics
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science
- Atmospheric Science
- Astronomy and Astrophysics
- Oceanography

### Cite this

*Journal of Geophysical Research C: Oceans*,

*108*(20), [4626]. https://doi.org/10.1029/2003JD003401

**On the angular radiance closure of tropical cumulus congestus clouds observed by the Multiangle Imaging Spectroradiometer.** / Zuidema, Paquita; Davies, Roger; Moroney, Catherine.

Research output: Contribution to journal › Article

*Journal of Geophysical Research C: Oceans*, vol. 108, no. 20, 4626. https://doi.org/10.1029/2003JD003401

}

TY - JOUR

T1 - On the angular radiance closure of tropical cumulus congestus clouds observed by the Multiangle Imaging Spectroradiometer

AU - Zuidema, Paquita

AU - Davies, Roger

AU - Moroney, Catherine

PY - 2003/10/27

Y1 - 2003/10/27

N2 - Monte Carlo reflectance simulations of three tropical cumulus congestus clouds reconstructed from Multiangle Imaging Spectroradiometer (MISR) data are compared to the domain-averaged MISR reflectance measurements. The goal of the comparison is to evaluate the nadir-view pixel cloud optical depth retrievals derived using plane-parallel radiative transfer theory, and the assumptions for vertically distributing the optical depth. Cloud heights are operationally retrieved using a stereo-imaging algorithm. The cloud heights and optical depths are at a 275 m spatial resolution, and for most simulations a vertical resolution of 250 m is applied. Five different but common three-dimensional cloud representations are assessed, using (1) a column vertical-mean volume extinction coefficient (β) value (the reference case), (2) a volume extinction coefficient proportional to the two-thirds power of height (the adiabatic assumption), (3) the adiabatic assumption at a 25 m vertical resolution, (4) a vertical-mean β retrieved from reflectances averaged over a (2.2 km)2 area, and (5) a vertical-mean β retrieved using off-nadir reflectances. An asymmetry about nadir in the observed reflectance means and skewnesses is not reproduced by any Monte Carlo simulation. The lack of symmetry can be related to differing proportions of unobscured sunlit and shadowed cloudy areas within the different views, even for these cases with viewing angles close to the perpendicular plane. The Monte Carlo simulations do not appear to capture the observed fraction of unobscured sunlit and shadowed cloudy areas, suggesting that radiatively significant cloud variability is occurring at scales smaller than the height field resolution of ±550 m. Results from the Monte Carlo simulation done at a higher vertical resolution are consistent with this. The cases examined also contain a nadir maximum in the observed reflectance skewnesses and a relative maximum for the observed nadir reflectances, attributed to the solar illumination of some optically thick cloud surfaces and to specular reflection pervading through the optically thin cloudy regions. This contrasts with previous modeling results that assume a Lambertian surface.

AB - Monte Carlo reflectance simulations of three tropical cumulus congestus clouds reconstructed from Multiangle Imaging Spectroradiometer (MISR) data are compared to the domain-averaged MISR reflectance measurements. The goal of the comparison is to evaluate the nadir-view pixel cloud optical depth retrievals derived using plane-parallel radiative transfer theory, and the assumptions for vertically distributing the optical depth. Cloud heights are operationally retrieved using a stereo-imaging algorithm. The cloud heights and optical depths are at a 275 m spatial resolution, and for most simulations a vertical resolution of 250 m is applied. Five different but common three-dimensional cloud representations are assessed, using (1) a column vertical-mean volume extinction coefficient (β) value (the reference case), (2) a volume extinction coefficient proportional to the two-thirds power of height (the adiabatic assumption), (3) the adiabatic assumption at a 25 m vertical resolution, (4) a vertical-mean β retrieved from reflectances averaged over a (2.2 km)2 area, and (5) a vertical-mean β retrieved using off-nadir reflectances. An asymmetry about nadir in the observed reflectance means and skewnesses is not reproduced by any Monte Carlo simulation. The lack of symmetry can be related to differing proportions of unobscured sunlit and shadowed cloudy areas within the different views, even for these cases with viewing angles close to the perpendicular plane. The Monte Carlo simulations do not appear to capture the observed fraction of unobscured sunlit and shadowed cloudy areas, suggesting that radiatively significant cloud variability is occurring at scales smaller than the height field resolution of ±550 m. Results from the Monte Carlo simulation done at a higher vertical resolution are consistent with this. The cases examined also contain a nadir maximum in the observed reflectance skewnesses and a relative maximum for the observed nadir reflectances, attributed to the solar illumination of some optically thick cloud surfaces and to specular reflection pervading through the optically thin cloudy regions. This contrasts with previous modeling results that assume a Lambertian surface.

KW - 3-D radiative transfer

KW - Cumulus congestus

KW - MISR

UR - http://www.scopus.com/inward/record.url?scp=36549052516&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=36549052516&partnerID=8YFLogxK

U2 - 10.1029/2003JD003401

DO - 10.1029/2003JD003401

M3 - Article

VL - 108

JO - Journal of Geophysical Research: Oceans

JF - Journal of Geophysical Research: Oceans

SN - 2169-9275

IS - 20

M1 - 4626

ER -