Radiometer may be used either with an f/16 telescope to measure thermal radiation from the surface of the dark moon or with a short-range optical system to measure thermal radiation from laboratory samples

Bird, A. N.

English

NASA Technical Reports Server

November 1967	 .	 Brief 67-10422 
'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. 
Infrared Radiometer 
A radiometer has been designed and constructed for 
use either with an f/16 telescope to measure thermal 
radiation from the surface of the dark moon or with 
a short-range optical system to measure thermal ra-
diation from laboratory samples. 
The basic scheme of the radiometer is the same 
whether it is mounted on a telescope or used with a 
laboratory optical system. Radiation from the col-
lecting optics is focused on a plate that has a 0.5-
mm-diameter aperture. Gold-coated mirrors are used 
to image the aperture on the thermal detectors, two 
gallium-doped germanium bolometers. The focal 
number of the radiometer optical system is f/16. To 
reduce background radiation, both the aperture plates 
and the optics can be cooled with liquid nitrogen to 
a temperature of approximately 1000 K. To provide 
continuous calibration, the radiometer has two in-
ternal calibration sources. A gold-coated chopper 
changes the direction of view of each detector so 
that each responds first to the incoming radiation 
then to one of the internal calibration sources. A 
magnetic pickup is used to sense the phase of the 
chopper and to provide a signal for demodulating the 
output from each detector. The signals from the two 
detectors are added in phase to produce an increased 
signal-to-noise ratio. Theoretically, the two-de-
tector system has a signal-to-noise ratio 1.4 times 
greater than that of a single detector system. The 
actual gain will depend on the similarity of tht sig-
nal and noise characteristics of the individual de-
tectors and on the precision of the alignment of the
optical system. The two detectors used in the radiom-
eter were well matched and had signal and noise char-
acteristics that differed only by a few percent. 
The spectral range of the radiometer is limited by 
the-transmission of the window that is mounted on the 
detector dewar and by the band pass of the interfer-
ence filter. The interference filters can be changed 
so that different band-pass filters can be used for 
making measurements in any spectral region up to the 
cutoff wavelength of the window. 
Notes: 
I. The radiometer has not yet been completely 
evaluated. 
2. Inquiries concerning this instrument may be di-
rected to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B67-10422 
Patent status: 
Inquiries about obtaining rights for the commer-
cial use of this invention may be made to NASA, 
Code GP, Washington, D. C. 20546. 
Source: A. N. Bird
of Southern Research Institute 
under contract to
Marshall Space Flight Center 
(M FS- 13373) 
Category 01 
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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Infrared radiometer

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