Datensatz

Zusammenfassung

This paper describes a tunable diode laser based dual channel photoacoustic (PA)
humidity measuring system called WaSul-Hygro primarily designed for aircraft based
environment research. It is calibrated for total pressures and water vapor (WV) vol-
5 ume mixing ratios (VMRs) possible during airborne applications. WV VMR is calculated
by using pressure dependent calibration curves and a cubic spline interpolation
method. Coverage of the entire atmospheric humidity concentration range which might
be encountered during airborne measurements is facilitated by applying an automated
sensitivity mode switching algorithm. The calibrated PA system was validated through
10 laboratory and airborne inter-comparisons, which proved that the repeatability, the estimated
accuracy and the response time of the system is 0.5 ppmV or 0.5% of the
actual reading (whichever value is the greater), 5% of the actual reading within the
VMR range of 1–12 000 ppmV and 2 s, respectively. The upper detection limit of the
system is about 85 000 ppmV, limited only by condensation of water vapor on the walls
15 of the 318 K heated PA cells and inlet lines. The unique advantage of the presented system is its applicability for simultaneous water vapor and total water volume mixing ratio measurements.