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Shixuan Pang and Hartmut Graßl

Abstract

A high-frequency Doppler sodar for precipitation measurements has been developed. Such a Doppler sodar (6–20 kHz) can almost always measure precipitation and turbulence spectra simultaneously. Therefore, the mean vertical wind and spectral broadening effects can be directly removed. As the acoustic refractive indices for ice and liquid water are almost the same, the acoustic retrieval of precipitation can also be applied to rain with small hail (e.g., diameter D < 10 mm) or large hail, but for the latter, neglecting the effects of different orientations and shapes of hailstones.

The authors’ single-board minisodar is based on the digital signal processing (DSP) technique. The first prototype has been continuously operated at a coastal weather station since 25 October 2002. For stratiform rain events, the minisodar showed good agreement with a Joss–Waldvogel disdrometer and an optical rain gauge. However, for convective heavy showers, the minisodar always observed higher rain rates.

The continuous, nonattended automatic operation of the minisodar has shown its capability for all kinds of precipitation measurements. The retrieval of precipitation rates for snow and graupel will be provided in a subsequent paper.

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Shixuan Pang, Hartmut Graßl, and Horst Jäger

Abstract

A common feature of all capacitance humidity sensors is their undesirable hysteresis effect due to the unequal adsorption and desorption of water vapor on the surfaces of their dielectric porous materials. To eliminate this error, an improved humidity sensor has been used composed of a commercial capacitive polymer sensor chip and an infrared (IR) radiation corrector emitting at a wavelength of 0.93 µm. The IR photons excite water molecule vibrations and destroy the bonds between water vapor and the material surface molecules, thus reducing residual hysteresis. Linearity is also improved, drift at high humidity is diminished, and response time is decreased.

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