Schematic diagram of the SAW frost-point hygrometer. Airflow is perpendicular to the plane of the diagram.
Signal attenuation and phase shift as a function of excitation frequency, near resonance, of the SAW device.
A sequence of frequency scans through the SAW resonance as progressively more water is condensed onto the active surface ( SAW devices). The scan shown in bold is for a dry surface and the vertical dotted line indicates a typical measurement frequency.
Calibration curves for two gold strip resistance thermometers on SAW devices. Straight-line fits are also shown, extended so that they are visible beyond the data points. For each of these two fits, .
Measured and calculated temperature-dependent shifts of the SAW device resonance frequency. Note that the shift is to lower frequency relative to room temperature. Digitization on the vertical axis is due to the resolution of the rf synthesizer chip.
Humidity profiles over Aberystwyth, Wales, on 19 October 2001 measured by three hygrometers, and the radiosonde ambient temperature profile. Inset: the water vapor volume mixing ratio (MR) derived from the SAW hygrometer measurements, temperature, and ozone partial pressure in the altitude range of .
Comparison of dew-/frost-point values measured by the SAW hygrometer and the radiosonde A-humicap (converted from relative humidity). Data from all nine flights using the SAW device are shown. The thin line indicates exact agreement and the bold line is a linear fit through the data points.
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