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Proceedings Paper

Z-domain numerical filter for removal of thermistor bolometer slow mode transients
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Paper Abstract

It is important to maintain measurements of Earth Radiation Budget parameters from orbit. Such measurements require broadband radiance detectors such as bolometers or thermopiles that rely on the conversion of radiant energy into heat. This heat conversion/conduction results in a thermal detector typically having an exponential time lag of a few milliseconds. However, it is found that there is often a far slower 'slow mode transient' response of around 300ms because the detector mounting material tends to rise in temperature as heat flows out of the detector to its surroundings. Hence this can cause the detector response to a constant input of radiance to continue increasing by a further 1%, for up to half a second after initial exposure. Using analysis of the heat flow out from a bolometer and through its mounting, the Laplace domain impulse response of the detector is derived that includes both first and second time constant effects. Transformation to the Z domain then allows design of a numerical filter to remove the second time constant effect while retaining that of the first time constant. Restoration of the ideal detector response is shown to be advantageous when applied to the output of thermistor bolometers onboard the Cloud's and the Earth's Radiant Energy System (CERES). It also allows more complete characterization of the response of such detectors using general calibration data. The design and use of such a filter is therefore highly applicable to any scanning bolometer or thermopile instrument with spurious slow mode effects.

Paper Details

Date Published: 22 August 2005
PDF: 7 pages
Proc. SPIE 5882, Earth Observing Systems X, 588213 (22 August 2005); doi: 10.1117/12.613981
Show Author Affiliations
Grant Matthews, Analytical Services and Materials (United States)
Kory Priestley, NASA Langley Research Ctr. (United States)
Peter Spence, Science Applications International Corp. (United States)

Published in SPIE Proceedings Vol. 5882:
Earth Observing Systems X
James J. Butler, Editor(s)

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