A radiation model was developed for retrieving cloud visible optical depth,
droplet effective radius, and cloud top emission temperature using AVHRR satellite
observations at 0.63, 3.7, and 11 ��m. The model was used to determine the sensitivity
of the retrieved properties to various approximations often employed in such retrievals.
Droplet effective radius appears to be the most sensitive to the commonly used
approximations. Cloud properties retrieved using a 16-stream scheme were within ��5%
of those retrieved using a 148-stream scheme. Cloud properties retrieved using double
Henyey-Greenstein phase functions were within ��10% of those retrieved using Mie
scattering. The retrieved cloud properties were used to investigate biases that arise when
partly cloudy pixels were assumed to be overcast and biases that arise due to oblique
satellite view angles. On average, cloud visible optical depths retrieved for partly cloudy
pixels were 40-60% of those retrieved for overcast pixels. Likewise, cloud liquid water
paths were 30-50%, droplet effective radii were 1-3 ��m smaller, and cloud top emission
temperatures were 2-4K larger. Cloud visible optical depths retrieved at 60�� satellite
zenith angles were 60-70% of those retrieved at nadir. The retrieved droplet effective
radii and cloud top emission temperatures varied little with changing satellite zenith
angle. For March 1989, cloud optical depths and cloud emission temperatures retrieved
for pixels overcast by single-layer, low-level clouds were negatively correlated. Cloud
optical depth, liquid water path, and droplet effective radius were positively correlated
with the sea surface-cloud top temperature difference.
The retrieved cloud properties were also compared for the spatial coherence,
CLAVR (Clouds from AVHRR), and a threshold method based on International Satellite
Cloud Climatology Project procedures. For regions containing single-layered cloud
systems, fractional cloud cover and cloud brightness temperatures derived by the
ISCCP-like threshold method were systematically larger than those derived by the
spatial coherence method, whereas cloud reflectivities were systematically smaller.
Cloud reflectivities and brightness temperatures derived by CLAVR and the spatial
coherence method were in better agreement. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/31695 |
| Date | 05 August 1997 |
| Creators | Chang, Fu-Lung |
| Contributors | Coakley, James A. Jr |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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