DESCARTES + µDIRAC + LABS + O3 SSS + H2O SAW + TDLAS

The SF series of multi-instrument balloon flights during HIBISCUS camapign were planned to be launched in late afternoon, and once reached float altitude left them to descend very slowly (0.5 meter per second or less) after their cooling at night for exploring the Tropical Tropopause Layer and the Upper Troposphere down to 12-14 km. The flight train was integrated by the following instruments:

DESCARTES stands for Détermination Et Séparation par Chromatographie lors de l'Analyse des Résultats des Traceurs Échantillonés dans la Stratosphère and was created for the measurement of long-lived trace gases (CFC-11, CFC-113, CCl4 and CH3CCl3) in the stratosphere by the University of Cambridge. The low weight of less than 20 kg and no need for telemetry make the instrument suitable for being launched on small balloons or fly as piggyback on larger balloons. The working principle is to let an amount of air pass through 16 sample tubes containing a Carboxen adsorbent. A valve allows only one tube at a time to be exposed to the air flow. Trace gases will then be trapped inside the sample tubes while the rest passes through. An on-board computer controls the sampling sequence, and also measures the flow of air, the pressure and temperature, the level of the batteries, and the state and position of the valve. After the flight, the data is downloaded from the computer, the sample sizes are determined and the sample box is connected to a gas chromatograph for quantification.

µDIRAC which stands for Determination In situ by Rapid Analytical Chromatography was designed by the University of Cambridge to measure halocarbons in the atmosphere. It evolved from the original design of other instruments named DESCARTES and DIRAC to meet the need for more flexible, autonomous, low power halocarbon analysis. It was originally designed for use on Montgolfier Infra Rouge (MIR) long duration balloons. However, it has proven versatile and has also been used in aircraft and ground-based deployments. The instrument is a temperature programmed gas chromatograph with electron capture detector (GC-ECD) that measures a range of halocarbons (including short-lived tracers having biogenic and anthropogenic sources) with measurement precision relative standard deviations ranging from ± 1% (CCl4) to ± 9% (CH3I).

LABS is a backscatter diode laser developed by the Istituto di Scienze dell'Atmosfera e del Clima (CNR-ISAC) and Ente Nazionale per le Nuove tecnologie, l'Energia e l'Ambiente (ENEA). It provides an in-situ measurement of the aerosol volume backscatter coefficient and aerosol depolarization at 532 nm. The aerosol volume backscatter coefficient detects the presence of aerosols in the air mass sampled, as well as a rough estimation of their quantity. The aerosol depolarization, being the ratio to what extent the main polarization of the laser is preserved in the backscattering process, gives information on the shape of the particles, and in some cases a coarse estimation of their dimensions as well.

The Surface Acoustic Wave (SAW) H2O sensor is a frost point hygrometer developed by the University of Cambridge that uses a surface acoustic wave (SAW) crystal instead of the classic cooled mirror and optical detector. The SAW crystal is placed, together with an accurate platinum resistance thermometer, onto a Peltier cooler. When cooled to the frost point, water vapour condenses onto the SAW surface, reducing the SAW oscillation frequency and amplitude, forming the basis of a feedback circuit. The temperature at which condensation occurs is then related to the ambient water vapour amount.

The Solid State Ozone Sensor (SSS O3) developed by the University of Cambridge consists of a thin tungsten oxide layer mounted on a small ceramic tile. When is heated to its operating temperature, oxygen vacancies, formed thermally at the oxide surface, create electron donor states, resulting in an increase in charge carrier concentration. Ozone molecules react filling the oxygen vacancies, thus decreasing the charge carrier concentration. Measuring the change in electrical resistance, lead to infer in a few seconds the ozone concentration. Its weight is less than 0.5 kg, excluding batteries.

The lightweight Tunable Diode Laser (TDLAS) developed by the National Physical Laboratory (NPL) uses near-infrared tunable diode lasers and an astigmatic Herriott cell to measure spectroscopic absorption over a pathlength of up to 101 m. The instrument is used for fast response measurements of atmospheric tracers on board balloons and aircrafts. The instrument was configured for water vapour measurements during HIBISCUS, using an all-metal gondola designed to minimise out-gassing. The measurements were made at a frequency of 0.7 Hz over three water vapour absorption lines.

Balloon launched on: 2/26/2004 at 20:00
Launch site: Meteorological Research Institute, Baurú, Sao Paulo, Brazil  
Balloon launched by: Centre National d'Etudes Spatiales (CNES)
Balloon manufacturer/size/composition: Zero Pressure Balloon model 3SF (heavy payload and short duration) 3.000 m3
Flight identification number: SF-3
End of flight (L for landing time, W for last contact, otherwise termination time): 2/27/2002
Campaign: HIBISCUS  

The SF3 mission was the last slow descent flight that was performed during the HIBISCUS campaign. The balloon was launched on 26 February at 17:00 local time and reached an altitude of 21.6 km shortly before sunset where it remained for about 1 hour before descending slowly for 3:45 hours down to 10 km.

• An overview of the HIBISCUS campaign Atmos. Chem. Phys., 11, 2309, 2011
• HIBISCUS campaign web site Laboratoire Atmosphères, Milieux, Observations Spatiales LATMOS