Discretized thermodynamic imaging for the measurement of precipitation and winds

Abstract. Precipitation and winds impart spatially and temporally variable thermodynamic signatures on surfaces. Here, we describe two new hotplate sensors, the DTI-pm and DTI-de, that sample energy flows using a discretized thermodynamic imaging (DTI) principle. Unlike prior single-element hotplate devices, DTI measurements are obtained at sufficiently high spatial resolution to separate component thermodynamic signatures. The DTI-pm is a sensor array of individually controlled micro-hotplates, each using pulse-width modulation to maintain a constant elevated temperature of each sensor element, measuring the power required to do so. The DTI-de uses an infrared camera that passively monitors radiative temperatures on a heated metal plate by exploiting the differential emissivity between metal and water; heat transfer physics is used to infer the power of thermodynamic cooling. Both techniques are shown here to be capable of measuring with exceptionally high accuracy and precision a wide range of precipitation characteristics, including mass, size, and the density of individual multi-phase hydrometeors, as well as continuous bulk precipitation rates and snow density. The DTI-de achieves a spatial resolution of 0.2 mm with a mass sensitivity of 1 µg, while the DTI-pm provides a spatial resolution of 1 mm and a mass sensitivity of 0.5 µg. Preliminary results suggest the potential for the DTI-pm and DTI-de to concurrently measure wind speed and direction.