An inverse-modelling approach for frequency response correction of capacitive humidity sensors in ABL research with small remotely piloted aircraft (RPA)

Abstract

Abstract. The measurement of water vapour concentration in the atmosphere is an ongoing challenge in environmental research. Satisfactory solutions exist for ground-based meteorological stations and measurements of mean values. However, carrying out advanced research of thermodynamic processes aloft as well, above the surface layer and especially in the atmospheric boundary layer (ABL), requires the resolution of small-scale turbulence. Sophisticated optical instruments are used in airborne meteorology with manned aircraft to achieve the necessary fast-response measurements of the order of 10 Hz (e.g. LiCor 7500). Since these instruments are too large and heavy for the application on small remotely piloted aircraft (RPA), a method is presented in this study that enhances small capacitive humidity sensors to be able to resolve turbulent eddies of the order of 10 m. The sensor examined here is a polymer-based sensor of the type P14-Rapid, by the Swiss company Innovative Sensor Technologies (IST) AG, with a surface area of less than 10 mm 2 and a negligible weight. A physical and dynamical model of this sensor is described and then inverted in order to restore original water vapour fluctuations from sensor measurements. Examples of flight measurements show how the method can be used to correct vertical profiles and resolve turbulence spectra up to about 3 Hz. At an airspeed of 25 m s −1 this corresponds to a spatial resolution of less than 10 m.

New Setup of the UAS ALADINA for Measuring Boundary Layer Properties, Atmospheric Particles and Solar Radiation

“…The sensor P14 has been well investigated in Wildmann et al [42], where a technique has been shown to reconstruct water vapor on the sensor surface by taking advantage of physical modeling. Furthermore, the limitations of this technique have been shown in Wildmann et al [42].…”

“…Furthermore, the limitations of this technique have been shown in Wildmann et al [42]. Because of these limitations, again a first order transfer function for humidity measurements is assumed, and ascents and descents were compared to determine time constants.…”

Quality assessment of MOZAIC and IAGOS capacitive hygrometers: insights from airborne field studies

“…After applying this function to the reference RH liquid time series, the ICH time series is reproduced for almost the complete cold flight sequence without getting worse in the warmer sequence of the flight. The remaining deviations might have their origins in calibration uncertainties, as well as in the potential deviations in the response time for conditions when the RH liquid is either increasing or decreasing (Wildmann et al, 2014) and uncertainties in the reference measurement.…”

Application of Different Turbulence Models Simulating Wind Flow in Complex Terrain: A Case Study for the WindForS Test Site

“…The overall endurance achieved with MASC is up to 90 min, which is associated with a flight distance of 135 km. MASC is standardly equipped with several subsystems specifically to measure the wind vector in three dimensions with a five-hole probe [35], air temperature with fast fine-wire probes [36], and humidity [37] with a capacitive sensor. The measurement equipment is able to resolve wind and temperature fluctuations up to 30 Hz and humidity fluctuations up to 3 Hz, all sampled with a rate of 100 Hz.…”