Detection of calibration drifts in spaceborne microwave radiometers using a vicarious cold reference

Authors
Citation
Cs. Ruf, Detection of calibration drifts in spaceborne microwave radiometers using a vicarious cold reference, IEEE GEOSCI, 38(1), 2000, pp. 44-52
Citations number
21
Categorie Soggetti
Eletrical & Eletronics Engineeing
Journal title
IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING
ISSN journal
01962892 → ACNP
Volume
38
Issue
1
Year of publication
2000
Part
1
Pages
44 - 52
Database
ISI
SICI code
0196-2892(200001)38:1<44:DOCDIS>2.0.ZU;2-U
Abstract
The coldest possible brightness temperatures observed by a downward-looking microwave radiometer from space are often produced by calm oceans under cl oud-free skies and very low humidity. This set of conditions tends to occur with sufficient regularity that an orbiting radiometer will accumulate a u seful number of observations within a period of a few days to weeks. Histog rams of the radiometer's coldest measurements provide an anchor point again st which very small drifts in absolute calibration can be detected. This te chnique is applied to the TOPEX microwave radiometer (TMR), and a statistic ally significant drift of several tenths of a Kelvin per year is clearly de tected in one of the channels. TMR housekeeping calibration data indicates a likely cause for the drift, as small changes in the isolation of latching ferrite circulators that are used in the onboard calibration-switch assemb ly. This method cars easily be adapted to other microwave radiometers, espe cially imagers operating at frequencies in the atmospheric windows, In addi tion to detecting long-term instrument drifts with high precision, the meth od also provides a means for cross-calibrating different instruments, The c old reference provides a common tie point, even between sensors operating a t different polarizations and/or incidence angles.