Computer program computes number of cloud-free elements in field-of-view and percentage of total field-of-view occupied by clouds. Human error is eliminated by using visual estimation to compute cloud statistics from aerial photographs

Liley, B.

Martin, C. D.

English

NASA Technical Reports Server

November 1971
	 Brief 71-10463 
NASA TECH BRIEF 
Goddard Space Flight Center
	 - 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
•	 be directed to the Technology Utilization Off i ce, NASA, Code KT, Washington, D.C. 20546. 
Cloud-Free Resolution Element Statistics Program 
The problem: 
To eliminate the human error inherent in using 
visual estimation to compute cloud statistics from 
aerial photographs. 
The solution: 
A computer program which computes the number 
of cloud-free elements in a field-of-view as a func-
tion of varying element size and computes the 
percentage of the total field-of-view occupied by 
clouds. 
How it's done: 
The program uses digital intensity data generated 
from the photograph by a spot scanner and trans-
ferred into six-bit words onto a magnetic tape. The 
intensity threshold for cloud background separation 
is selected, and the intensity data is used in con-
junction with this threshold to convert intensity 
levels into cloud and no-cloud integers. Roads and 
spurious points are eliminated by converting to 
zeros those cloud-scan lengths which are less than 
empirically determined values. Insignificant cloud
amounts are also eliminated. The accumulated cloud-
free resolution elements are normalized relative to 
the total number or resolution elements to obtain 
cloud-free percentages. 
Notes: 
1. This program is written in FORTRAN IV for 
use on the IBM-360 system. 
2. Requests for further information may be directed 
to:
COSMIC 
112 Barrow Hall 
University of Georgia 
Athens, Georgia 30601 
Reference: B71-10463 
Patent status: 
No patent action is contemplated by NASA. 
Source: C. D. Martin and B. Liley of

North American Rockwell Corp.

under contract to

Goddard Space Flight Center

(G SC- 11494) 
Category 09 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
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Cloud-free resolution element statistics program

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