An improved non-contact thermometer and hygrometer with rapid response

Previously (Underwood et al 2015 Meteorol. Appl. 22 830) we reported first tests of a device capable of simultaneous, non-contact, temperature and humidity (NCTAH) measurements in air. The device used an acoustic thermometer and a tuneable diode laser absorption spectrometer (TDLAS), a combination which should be capable of an extremely rapid response to changes in humidity as it does not require moisture in a solid-state matrix to equilibrate with the surrounding air. In this paper we report recent developments of the instrument focussed on reducing its response time so that it can be used as a reference instrument for assessing the response time of conventional humidity sensors. In addition, the interdependence of the temperature and humidity estimates is now accounted for in real-time using an iterative procedure, which eliminates the need for data post-processing.