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A combined non-contact acoustic thermometer and infrared hygrometer for atmospheric measurements.

Underwood, R; Gardiner, T; Finlayson, A; Few, J; Wilkinson, J; Bell, S A; Merrison, J*; Iverson, J J*; de Podesta, M (2015) A combined non-contact acoustic thermometer and infrared hygrometer for atmospheric measurements. Meteorological Applications, 22. pp. 830-835.

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Temperature and humidity measurements in the upper atmosphere are of critical importance for understanding the climate of the Earth. However such measurements are difficult for several reasons. Firstly, measurements are typically made on a rising sonde which carries moisture upwards with it, compromising measurements in the dry stratospheric environment. Secondly, the difference in the time-constants of thermometers and hygrometers on a rising sonde leads to difficulties in determining the extent of saturation of the air - a critical variable for understanding cloud formation. Finally the effects of insolation and the poor thermal contact with the air compound the other measurement problems.

To address these issues we have designed a new combined temperature and humidity sensor which makes rapid measurements in approximately 10 litres of air of without requiring thermal contact.

The temperature measurements are made using an acoustic interferometer which is servo-controlled at around 15 kHz to keep a fixed number of wavelengths in the measurement volume. The volume being measured is that between a parabolic dish 20 cm in diameter and an acoustic mirror 50 cm away. These elements are held together in a carbon-fibre open frame.

Humidity measurements are made using a Tuneable Diode Laser Absorption Spectrometer (TDLAS) which interrogates the same volume of air through holes in the mirror and parabola.

Here we report tests on the device at NPL at a pressure of 1 atmosphere, and from simulated ascents through the atmosphere at the MARS Simulation facility at the University of Aarhus, Denmark.

Item Type: Article
Keywords: Climate, Temperature, Hygrometer, Moisture, atmosphere, stratosphere.
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Identification number/DOI: 10.1002/met.1513
Last Modified: 02 Feb 2018 13:13
URI: http://eprintspublications.npl.co.uk/id/eprint/7003

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