Multispectral analysis of nighttime low clouds over the ocean.
Authors
Dykes, James D.
Subjects
Low cloud analysis
Radiative transfer
Fog
Satellite imagery
Radiative transfer
Fog
Satellite imagery
Advisors
Wash, Carlyle H.
Date of Issue
1991
Date
March 1991
Publisher
Monterey, CA; Naval Postgraduate School
Language
en_US
Abstract
Multispectral imagery is used for the analysis of nighttime low clouds whose
cloud top temperatures are similar to that of the ocean surface. At night
AVHRR channel 3 (3.7 pm) and channel 4 (10.8 /^m) brightness temperature
differences distinguish the presence of low stratus and fog from the ocean surface
improving upon the channel 4 analysis alone. However, the effect of moisture
attenuation in channel 4 offsets this temperature difference and impact thresholds
which determine low cloud extent. Radiative transfer simulations using different
moisture profiles helped to determine threshold adjustment. This thesis uses one
of two sets of thresholds depending on moisture extent in an enhancement scheme
to discriminate clear areas, and scattered, broken and overcast clouds on different
summertime imagery cases over the ocean. Two cases are illustrated thoroughly
and the technique was also applied to eight other cases. Results agreed for the
most part with surface observations and visible GOES from the previous day.
The multi-channel technique improved most or all deficiencies of the single
channel analysis in all the cases except one where only some deficiencies were
improved. The color enhancement provides a clear, qualitative picture of
nighttime low cloud.
Type
Thesis
Description
Series/Report No
Department
Department of Meteorology
Organization
Naval Postgraduate School (U.S.)
Identifiers
NPS Report Number
Sponsors
Funder
Format
42 p.;28 cm.
Citation
Distribution Statement
Approved for public release; distribution is unlimited.
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.