AquaVIT-4 : Participating instruments

Pico-Light H2O (GSMA/DT-INSU, PI: Pr. G. Durry, co-PI: Dr. M. Ghysels-Dubois, PM: Nadir Amarouche)

Pico-Light H2O (PI: G. Durry, co-PI: M. Ghysels-Dubois): Is the lightweight successor of Pico-SDLA H2O (Durry et al., 2008b; Ghysels et al., 2016).  Pico-SDLA H2O was tested against other hygrometers, both in flight and in an atmospheric simulation chamber (Behera Abhinna K. et al., 2018; Berthet et al., 2013; Durry et al., 2008a; Fahey et al., 2014; Ghysels et al., 2016; Korotcenkov, 2018). Pico-Light H2O is a tunable diode laser spectrometer which allows to measure in situ water vapor mixing ratio using direct absorption spectroscopy over a 1-m optical path in ambient air. It has been developed since 2017 by DT-INSU (Division Technique de l’INSU, UAR 855, Meudon, France) and GSMA (UMR CNRS 7331, Reims, France). The in situ mixing ratio is retrieved from the processing of recorded atmospheric spectra of two water vapor lines:  the 413←414 H216O line at 3802.96561 cm-1(troposphere), and the 202←101H216O line at 3801.41863 cm-1(upper troposphere and stratosphere). The novelty of Pico-Light H2O lies in its new electronics, lighter weight (2.7 kg), simpler mechanical structure, and improved energy management. The dramatic weight reduction made it possible to fly the instrument from a small rubber weather balloon. Such a hygrometer launched on small balloons could make frequent measurements in difficult meteorological conditions and at low cost.

The mean relative difference between Pico-Light and MLS v4.2 is 7.5% between 38 hPa and 100 hPa. Between 68 hPa and 146 hPa over Aire-sur-l’Adour, the mean difference is 10.8 %, similar to the mean bias reported in the same altitude range by (Yan et al., 2016) (mean bias: 11%). For altitudes higher than 19.6 km (<56 hPa), the mean bias between Pico-Light and MLS is larger than the one reported by (Yan et al., 2016), probably due to a moderate contamination of Pico-Light due to outgassing (see the discussion in section 6.2). For pressure levels greater than 100 hPa, differences can reach 80% due to the coarse vertical resolution of MLS. The measurement precision is of 277 ppbv for an integration time of 8 ms (unitary spectra) and 130 ppbv for an integration time of 1s.

Figure 1: a) Picture of Pico-Light H2O under rubber balloon on February 19, 2019 from the CNES Aire-sur-l’Adour balloon facility (southern france). b) Details of the hygrometer.
Figure 4: The Pico-Light H2O instrument with Nadir Amarouche (DT-INSU, right), Fabien Frérot (DT-INSU, in the middle) and Mélanie Ghysels-Dubois (GSMA, left).

References :

1- Durry, G., Amarouche, N., Joly, L. et al. Laser diode spectroscopy of H2O at 2.63 μm for atmospheric applications. Appl. Phys. B 90, 573–580 (2008).

2- Ghysels, M., Riviere, E. D., Khaykin, S., Stoeffler, C., Amarouche, N., Pommereau, J.-P., Held, G., and Durry, G.: Intercomparison of in situ water vapor balloon-borne measurements from Pico-SDLA H2O and FLASH-B in the tropical UTLS, Atmos. Meas. Tech., 9, 1207–1219,, 2016.

3- Ghysels, M., Durry, G., Amarouche, N., Samake, J.-C., Frérot, F., and Rivière, E. D.: A lightweight balloon-borne mid-infrared hygrometer to probe the middle atmosphere: Pico-Light H2O. Comparison with Aura-MLS v4 and v5 satellite measurements, Atmos. Meas. Tech. Discuss. [preprint],, in review, 2020.

SAWPhy hygrometer (LMD, PI: Dr. A. Hertzog):

SAWfPHY is a frost-point hygrometer developed at LMD (UMR CNRS 8539). The technique relies on the detection of a frost layer on the surface of a cooled mirror, leading to the determination of the air frost point temperature. Common frost point hygrometer use optical techniques to detect the frost layer. SAWfPHY uses the interaction between the frost layer and acoustic wave propagating at the surface of a quartz crystal. This technique, allows to detect layers 10 to 100 times thinner than with optical methods. The hygrometer is in operation since 2019 and is still under development. The detection principle of the instrument has been tested under open stratospheric balloon in Kiruna on April 2010 and March 2011. It is currently participating to the Stratéole-2 equatorial balloon campaign.

Figure 3: Picture of the SAWPhy hygrometer
Figure: The SAWfPhy instrument (right) next to pico-Light H2O at the bottom of the main vessel during AQUAVIT-4.

ALBATROSS (PI: Dr. B. Tuzson): 

The Quantum-Cascade Laser Absorption Spectrometer (QCLAS) is a compact instrument for balloon-borne measurements of water vapor in the upper troposphere and lower stratosphere (UTLS), developed at Empa. The instrument is based on direct laser absorption spectroscopy in the mid-IR spectrum (wavelength 6 μm),and relies on a segmented circular multipass cell (optical path length 6 m) that was specifically developed to meet the stringent requirements posed by the harsh environmental conditions of the UTLS. Quick response and minimal interference by water vapor outgassing from surfaces are achieved by an open-path approach. An elaborate thermal management system ensures excellent internal temperature stability despite of outside temperature variations of up to 80 K. With a total weight of 3.9 kg, the QCLAS is a fully independent system, operating autonomously for the duration of a balloon flight. The first two successful test flights were performed in December 2019 from the meteorological observatory of Lindenberg (Germany).

Figure 5 : Picture of the QCLAS hygrometer (EMPA, Switzerland).
Figure 6: The ALBATROSS instrument and Simone Brunamonti (EMPA) at AIDA during AQUAVIT-4.

References :

1- Graf, M., Emmenegger, L., and Tuzson, B.: Compact, circular, and optically stable multipass cell for mobile laser absorption spectroscopy, Opt. Lett., 43, 2434–2437,, 2018.

2- Graf, M., Scheidegger, P., Kupferschmid, A., Looser, H., Peter, T., Dirksen, R., Emmenegger, L., and Tuzson, B.: Compact and lightweight mid-infrared laser spectrometer for balloon-borne water vapor measurements in the UTLS, Atmos. Meas. Tech., 14, 1365–1378,, 2021.

NASA Langley Diode Laser Hygrometer (DLH) 

The NASA Langley Diode Laser Hygrometer (DLH) is an external, open-path near-infrared tunable diode laser absorption instrument which has flown on several aircraft over the past 25+ years. There are several versions of DLH, as they are designed and constructed specifically for each aircraft, but in general, each one consists of a transmitter/receiver and a quasi-retroreflector, between which is the two-pass optical absorption path. The DLH instrument which was used during AquaVIT-4 (DLH-WB) is the one which flies on the NASA WB-57F aircraft, a platform which can reach approximately 20 km altitude during research flights lasting up to 6 hours or more. The transceiver in the DLH-WB is mounted inside an airfoil-shaped fin which is mounted beneath the aircraft wing, and the retroreflective film is typically located on a thin antenna-like fin mounted beneath an instrument pod on the same wing. Optical paths on this aircraft have ranged from approximately 13 m to 18 m. For AquaVIT-4, the DLH-WB transceiver assembly (which also contains the laser itself and all data acquisition and control) was mounted outside the chamber in the cold zone, and the optical beam was passed through a custom-coated plane parallel window. The retroreflective film was mounted on the inside of a window blank on the opposite side of the chamber, resulting in a two-pass optical path in the chamger of approximately 9.4 m. The short path between the instrument transceiver window and the facility window was purged continuously with synthetic air. External heaters were added to the transceiver assembly to maintain a minimum temperature of approximately -20 degrees C while the instrument was unpowered during the overnight hours.

Figure: the NADA DLH instrument in the cold part, outside the main vessel, at AIDA together with Glenn Diskin (NASA Langley) during AQUAVIT-4