A portable laser absorption sensor for quantitative measurement of ambient temperature and humidity

Abstract

A portable and sensitive laser absorption sensor is developed for quantitative measurement of ambient temperature and humidity. The H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O absorption lines in the combination and overtone bands were comprehensively investigated and a promising line pair (7181.16 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 7185.60 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) was selected to ensure sensitive measurement with high accuracy and low uncertainty within the temperature range of 0-30 °C. A single distributed feedback laser near 1392 nm was used to access the selected line pair. Scanned wavelength direct absorption spectroscopy was used for temperature and humidity measurement. A Multi-line Vogit-fitting strategy was adopted to reduce the fractional fitting residual. The sensor performance was firstly evaluated numerically at different noise levels (0-10%) and then demonstrated experimentally under the temperature range of 0-30 °C and relative humidity range of 10-50 %. The temperature and humidity as measured with the laser sensor were in good agreement with those from the negative temperature coefficient (NTC) thermistor and commercial hygrometer, respectively. The sensor was then applied to perform in situ and real-time measurements of ambient temperature and humidity outside the lab. With a time response of 1s, the sensor demonstrated a precision (uncertainty) of 0.150.2 °C (0.09-0.2 °C) and 0.5-1 % (0.25-0.8%) for temperature and relative humidity, respectively. The sensor is expected to have potential applications in the vehicle wind tunnel and environmental monitoring.