System employing digital space correlation to suppress false target signals in a point-target tracking device is a reliable method for discriminating a distant target from false targets in the field of view of an infrared detection system or tracking device

Maxwell, R. F., Jr.

English

NASA Technical Reports Server

Photc 
Signa tout 
December 1966
	 Brief 66-10622 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Point-Source Detection System Rejects Spatially Extended Radiation Sources 
Point Target
Photocell 
Detectors
MMMMMMMMMM 
mmmammmmmm 
MMMOMMMUMM 
an Mannen ø[UUøJ rnnnrn
Cloud
Search Field 
FIGURE 1	 FIGURE 2	 FIGURE 3 
The problem: 
To devise a reliable method for discriminating a 
distant (point source) target from false (spatially 
extended) targets in the field of view of an infrared 
detection system or tracking device. Various spatial 
discrimination methods (spatial filtration, pulse-length 
discrimination, area cancellation, and analog space 
correlation) that have been used to distinguish char-
acteristic differences between the signals from a point 
target and those from larger-area targets require 
generally complex circuitry and are not entirely suit-
able for tracking a reentering space vehicle. 
The solution: 
A system employing digital space correlation to 
suppress false target signals in a point-target tracking 
device. 
How it's done: 
The search field (Figure 1), containing the point 
target to be tracked and a cloud representing an
extended-area false target, is divided into a matrix 
of rows and columns of elemental fields of view. As 
shown in Figure 2, digital values are assigned to the 
matrix elements. That is, the elements containing 
no target radiation are designated by zeroes, and the 
elements in which target radiation appears are des-
ignated by ones. In accordance with the method 
described below, adjacent elements (such as those 
corresponding to the cloud) having targets are 
eliminated. Only the individual element corresponding 
to the point target is accepted. 
Photocells mounted in a column are moved across 
the field matrix to scan the elements sequentially. 
When target radiation of sufficient intensity (above a 
threshold value) impinges on a photocell that is 
sampling a particular matrix element, the photocell 
will emit a signal pulse. If no radiation, or only a 
very low amount of radiation impinges on the photo-
cell, the cell's output will be rejected. The pulses 
are fed to an or gate and to a delay line having seven 
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19660000620 2020-03-11T17:46:06+00:00Z
outputs that are also applied to the or gate (Figure 3). 
The output from the or gate is applied to the inhibit 
input of an inhibit gate, and an eighth signal output 
from the delay line is coupled to the signal input of 
the inhibit gate. When there is a signal correspondence 
between one input to the or gate and the signal out-
put from the delay line to the inhibit gate, no signal 
will pass through the inhibit gate. This correspond-
ence occurs only for signals from photocells that 
sample an array of adjacent matrix elements inter-
cepting an extended area target. 
Note: 
Inquiries concerning this system and modifications 
that will resolve certain ambiguous cases may be di-
rected to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B66-10622
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: R. F. Maxwell, Jr.

of Westinghouse Electric Corporation

under contract to

Goddard Space Flight Center

(GSFC-486) 
Brief 66-10622	 Category 01


Point-source detection system rejects spatially extended radiation sources

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server