Diode Laser Hygrometer

Status

Status
Operational
Operated By
PI

The DLH has been successfully flown during many previous field campaigns on several aircraft, most recently ACTIVATE (Falcon); FIREX-AQ, ATom, KORUS-AQ, and SEAC4RS (DC-8); POSIDON (WB-57); CARAFE (Sherpa); CAMP2Ex and DISCOVER-AQ (P-3); and ATTREX (Global Hawk). This sensor measures water vapor (H2O(v)) via absorption by one of three strong, isolated spectral lines near 1.4 μm and is comprised of a compact laser transceiver and a sheet of high grade retroflecting road sign material to form the optical path. Optical sampling geometry is aircraft-dependent, as each DLH instrument is custom-built to conform to aircraft geometric constraints. Using differential absorption detection techniques, H2O(v) is sensed along the external path negating any potential wall or inlet effects inherent in extractive sampling techniques. A laser power normalization scheme enables the sensor to accurately measure water vapor even when flying through clouds. An algorithm calculates H2O(v) concentration based on the differential absorption signal magnitude, ambient pressure, and temperature, and spectroscopic parameters found in the literature and/or measured in the laboratory. Preliminary water vapor mixing ratio and derived relative humidities are provided in real-time to investigators.

Instrument Type
Measurements
Recent Missions
(P-3 Orion - WFF)
;
(DC-8 - AFRC)
;
(DC-8 - AFRC)
;
(P-3 Orion - WFF)
;
(P-3 Orion - WFF)
;
(WB-57 - JSC)
Point(s) of Contact
Range of Measurement
In situ
Measurement Sampling Rate
100.00 Hz
Weight
48.00 kg
Size
43.00 cm (L) x 33.00 cm (W) x 23.00 cm (H)
Power:
300.00 W
Has Pressurized Canisters? Yes
Location
Window 410L on DC-8; Zenith Port on P-3B; Left Wing Hatch on WB-57; Zone 25 on Global Hawk 872; SciFly Window on HU-25A.
Notes
DLH makes measurements using tunable diode laser absorption
Mission-Specific Writeups