The development and evaluation are reported of phase shift techniques based on the Fourier transform for the estimation of cloud motion from geosynchronous meteorological satellite photographs. An alternative approach to cloud motion estimation, involving thresholding, was proposed and studied

Lo, R. C.

Rosenfeld, A.

English

NASA Technical Reports Server

University of Maryland
College Park, Maryland 20742
Fourier transform techniques
for the inference of cloud motion
Final Technical Report
covering the period
October 1972-December 1974
NGR-21-002-378
Principal Investigators:
R. C. Lo 1
A. Rosenfeld
Computer Science Center w
The NASA Technical Officer for this grant is
Dr. Albert Arking, Code 911
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
* (NASA-CR-142077) FOURIER TRANSFORM N75-17041
,TECHNIQUES FOR THE INFERENCE OF CLOUD MOTION
,Final Technical Report, Oct. 1972 
- Dec.
1974 (Maryland Univ.) 5 p HC $3.25 CSCL 04B Unclas
--.. G3/47 09615
https://ntrs.nasa.gov/search.jsp?R=19750008969 2020-03-22T22:54:17+00:00Z
The main concern of this project was the development and
evaluation of phase shift techniques based on the Fourier trans-
form for the estimation of cloud motion from geosynchronous
meteorological satellite photographs. An alternative approach to
cloud motion estimation, involving thresh ldi ng, was also proposed
and studied ,Further details can ,be found in :th, 1fl i tng! abstracts
of he el rt t'en .6;1on pte  ec"t:
1. A study of the application of Fourier transforms to cloud
movement estimation from satellite photographs
R. C. Lo and J. A. Parikh
(Computer Science Center Technical Report 242)
May, 1973
A preliminary study of the application of Fourier
transforms to cloud motion estimation based on two successive
satellite photographs is conducted. The primary techniques
of cloud motion estimation developed are an analysis of the
cross-covariance function and a Fourier phase-difference tech-
nique. Computer programs utilizing these techniques are
developed.
Simulations of various changes of cloud features which
are often observed in the real atmosphere are made. The
cross-covariance and phase-difference techniques are applied
to these cases. The results are analyzed and discussed. Since
real cloud feature changes in the atmosphere can usually be
regarded as one or a combination of these simulated situations,
results from the present study are expected to be revealing
and beneficial to the analysis of real data applications.
Such applications and other further studies are planned.
2. Applications of Fourier transform methods of cloud movement
estimation to simulated and satellite photographs
R. C. Lo, J. Mohr and J. A. Parikh
(Computer Science Center Technical Report 292)
January, 1974
Spectral filters of different types and sizes are
applied to Fourier transforms of successive simulated and
real pictures in an attempt to isolate clouds of certain
types, and thus avoid the inaccuracy of Fourier transform
method estimates of cloud movement, caused by the presence
of a mixture of cloud motions in the pictures. -The- Fourier
transform methods utilized are a cross-correlatlon technique
and a phase shift technique. They are applied to the filtered
transforms for the estimation of cloud motion. The simulations
included in this report are designed to examine the abilities
and limits of the filtering technique. The real cases chosen
represent different typical cloud phenomena observed in the
atmosphere. The results obtained in each case are analyzed
and discussed.
3. Applications of enhancement and thresholding techniques to
Fourier transform cloud motion estimation
R. C. Lo and J. Mohr
(Computer Science Center Technical Report 326)
September, 1974
Two approaches have been developed to process pairs of
successive satellite photographs before they are utilized through
Fourier transform techniques to derive cloud motion estimates.
The purpose of this pre-processing is to obtain better cloud
motion estimates than those obtained from direct methods. The
first approach attempts to improve the definition of cloud
features in the satellite photographs. It accomplishes its
task by modifying the gray level histogram of the real picture
into an artificial frequency distribution which is defined
according to characteristics that are desired in the resultant
modified pictures. The second approach attempts to isolate cloud
motion by separating clouds of different types in the original
photographs. A threshold technique is utilized to
accomplish this purpose. The Fourier transform techniques are
then applied to pairs of pre-processed pictures for cloud
motion estimation. The results are analyzed and discussed.
4. An evaluation of Fourier transform techniques for cloud
motion estimation
A. A. Arking, R. C. Lo and A. Rosenfeld
(Computer Science Center Technical Report 351)
January, 1975
Two techniques based on the Fourier transfor"mwere
developed for the estimation of cloud motion from patrs of
pictures. They are the cross-correlation method and.the
phase shift method. They have been applied to simulated. and
real satellite data. Because of the restrictive assumptions
involved in these techniques, the results were not very
satisfactory. A frequency domain filtering technique and
an enhancement technique were then developed for the
improvement of the cloud motion estimates. The results of
their application are discussed, and suggestions for future
improvements are made.
5. The application of a thresholding technique in cloud motion
estimation from satellite observations
Robert C. Lo
(Computer Science Center Technical Report 357)
February 1975
One of the greatest difficulties in cloud motion estima-
tion from satellite photographs is the existence of mixtures
of clouds. A thresholding technique based on brightness
observations, using a non-linear least squares regression
approach, is presented in this study. The application of this
technique not only produces results consistent with those
obtained from other independent techniques, but also provides
information about the vertical wind profile. Further develop-
ment of an automatic method of estimating parameters which are
needed as input for the least squares regression approach is
also suggested. A preliminary study of a two-dimensional
thresholding technique based on bivariate frequency
distribution functions is also included in this report.
Results from this study are promising. Further de-
velopment of it should be pursued.


Fourier transform techniques for the inference of cloud motion

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