HAI, a new airborne, absolute, twin dual-channel, multi-phase TDLAS-hygrometer: background, design, setup, and first flight data
The novel Hygrometer for Atmospheric Investigation (HAI) realizes a unique concept for simultaneous gas-phase and total (gas-phase + evaporated cloud particles) water measurements. It has been developed and successfully deployed for the first time on the German HALO research aircraft. This new instr...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-01-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/10/35/2017/amt-10-35-2017.pdf |
| Summary: | The novel Hygrometer for Atmospheric
Investigation (HAI) realizes a unique concept for simultaneous
gas-phase and total (gas-phase + evaporated cloud particles) water
measurements. It has been developed and successfully deployed for the first
time on the German HALO research aircraft. This new instrument combines
direct tunable diode laser absorption spectroscopy (dTDLAS) with a
first-principle evaluation method to allow absolute water vapor measurements
without any initial or repetitive sensor calibration using a reference gas
or a reference humidity generator. HAI contains two completely independent
dual-channel (closed-path, open-path) spectrometers, one at 1.4
and one at 2.6 µm, which together allow us to cover the entire
atmospheric H<sub>2</sub>O range from 1 to 40 000 ppmv with a single instrument.
Both spectrometers each comprise a separate, wavelength-individual
extractive, closed-path cell for total water (ice and gas-phase)
measurements. Additionally, both spectrometers couple light into a common
open-path cell outside of the aircraft fuselage for a direct, sampling-free,
and contactless determination of the gas-phase water content. This novel
twin dual-channel setup allows for the first time multiple self-validation
functions, in particular a reliable, direct, in-flight validation of the
open-path channels. During the first field campaigns, the in-flight
deviations between the independent and calibration-free channels (i.e.,
closed-path to closed-path and open-path to closed-path) were on average in
the 2 % range. Further, the fully autonomous HAI hygrometer allows
measurements up to 240 Hz with a minimal integration time of 1.4 ms. The
best precision is achieved by the 1.4 µm closed-path cell at 3.8 Hz
(0.18 ppmv) and by the 2.6 µm closed-path cell at 13 Hz (0.055 ppmv).
The requirements, design, operation principle, and first in-flight
performance of the hygrometer are described and discussed in this work. |
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| ISSN: | 1867-1381 1867-8548 |