Universität zu Köln

Paine, Scott N., Turner, David D. and Kuechler, Nils (2014). Understanding Thermal Drift in Liquid Nitrogen Loads Used for Radiometric Calibration in the Field. J. Atmos. Ocean. Technol., 31 (3). S. 647 - 656. BOSTON: AMER METEOROLOGICAL SOC. ISSN 1520-0426

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Abstract

An absorbing load in a liquid nitrogen bath is commonly used as a radiance standard for calibrating radiometers operating at microwave to infrared wavelengths. It is generally assumed that the physical temperature of the load is stable and equal to the boiling point temperature of pure N-2 at the ambient atmospheric pressure. However, this assumption will fail to hold when air movement, as encountered in outdoor environments, allows O-2 gas to condense into the bath. Under typical conditions, initial boiling point drift rates of order 25 mK min(-1) can occur, and the boiling point of a bath maintained by repeated refilling with pure N-2 can eventually shift by approximately 2 K. Laboratory bench tests of a liquid nitrogen bath under simulated wind conditions are presented together with an example of an outdoor radiometer calibration that demonstrates the effect, and the physical processes involved are explained in detail. A key finding is that in windy conditions, changes in O-2 volume fraction are related accurately to fractional changes in bath volume due to boiloff, independent of wind speed. This relation can be exploited to ensure that calibration errors due to O-2 contamination remain within predictable bounds.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Paine, Scott N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Turner, David D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kuechler, Nils UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-443849
DOI:	10.1175/JTECH-D-13-00171.1
Journal or Publication Title:	J. Atmos. Ocean. Technol.
Volume:	31
Number:	3
Page Range:	S. 647 - 656
Date:	2014
Publisher:	AMER METEOROLOGICAL SOC
Place of Publication:	BOSTON
ISSN:	1520-0426
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language PHASES; WATER Multiple languages Engineering, Ocean; Meteorology & Atmospheric Sciences Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/44384