FLASH-B + COBALD + LOAC

The balloon carried three instruments FLASH-B, COBALD and LOAC

The FLASH-B (FLuorescence Advanced Stratospheric Hygrometer for Balloon) instrument is a light-weighted Lyman-alpha hygrometer (~2 kg) developed by the Central Aerological Observatory, Dolgoprudny, Russia. The instrument is based on the fluorescent method, which uses the photodissociation of H2O molecules at a wavelength < 137 nm followed by the measurement of the fluorescence of excited OH radicals. The source of Lyman-alpha radiation (121.6 nm) is a hydrogen discharge lamp, while the detector of OH fluorescence at 308-316 nm is a Hamamatsu R647-P photomultiplier run in photon counting mode with a narrow band interference filter selecting the fluorescencespectral region. The intensity of the fluorescent light sensed by the photomultiplier is directly proportional to the water vapour mixing ratio under stratospheric conditions (10-150 hPa) with small oxygen absorption (3% at 50 hPa). The H2O measurement range is limited to pressures lower than ~300 hPa due to strong Lyman-alpha absorption in the lower troposphere. Measurements are only made at nighttime.

COBALD (Compact Optical Backscatter Aerosol Detector) is a lightweight backscatter sonde developed at ETH Zurich. With a total weight of approximately 550 g including batteries, the instrument can be flown on operational weather balloons. COBALD measures molecular, aerosol and cloud particle backscatter in the atmosphere from the ground to the level of balloon burst. Two LEDs with 250 mW optical power each emit light at wavelengths of 455 and 870 nm in the blue and near infrared spectral range. To register the backscattered light, a photodiode is placed between the LEDs, and the associated optics establishes an overlap region at distances larger than 0.5 m in front of the instrument. So far, the instrument is designed for applications during night-time only as solar radiation saturates the detector. The molecular number density is determined from temperature and pressure recorded simultaneously by the hosting radiosonde.

LOAC (Light Optical Aerosols Counter) is an optical particle/sizer counter developed by Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPCE-CNRS) from France. The system is light and compact enough to perform measurements not only at the surface but under all kinds of balloons in the troposphere and in the stratosphere. It performs observations at two scattering angles. The first one is around 12°, and is almost insensitive to the nature of the particles; the second one is around 60° and is strongly sensitive to the refractive index of the particles. By combining measurement at the two angles, it is possible to retrieve accurately the size distribution and to estimate the nature of the dominant particles (droplets, carbonaceous, salts and mineral particles) in several size classes. This speciation is based on calibration charts obtained in the laboratory.

LOAC is a modular instrument, for which some parts can be changed depending on the measurements conditions. For measurements under balloon or on the ground in low wind conditions, the aerosols are collected by a metal profiled inlet designed to optimize the sampling conditions when oriented in the wind direction. The particles are drawn up to the optical chamber through an isostatic tube by a small pump. The pump is connected to the exit of the optical chamber by a flexible plastic tube. For measurements in windy and rainy conditions, the inlet can be replaced by a total suspended particulate or TSP inlet rejecting rain droplets and particles greater than 100 µm. For long-duration measurements, the small pump can be replaced by a robust pump. The sampled air crosses a laser beam of 25 mW working at the wavelength 650 nm. The scattered light is recorded by two photodiodes at scattering angles of respectively 12º and 60º. Instead of using lenses to collect the light, the photons travel directly to the photodiodes through pipes, providing fields of view with a few degrees. The collecting area of the photodiodes is larger than the diameter of the pipes. This system prevents optical misalignment problems in case of vibrations and strong temperature variations like those encountered during atmospheric balloon flights.

To minimize its weight, the optical chamber is encased in plastic Delrin. The weight, including the pump, is of 350 grams.

Balloon launched on: 2/11/2013
Launch site: Meteorological Research Institute, Baurú, Sao Paulo, Brazil  
Balloon manufacturer/size/composition: Weather Balloon  
End of flight (L for landing time, W for last contact, otherwise termination time): 2/11/2013
Campaign: TRO-PICO  

This flight was part of the TRO-Pico campaign performed in Brazil between 2012 and 2013. It aims at studying deep convection in the tropics and more precisely, the impact of overshooting convection in the lower stratosphere on the stratospheric water budget, from the local to the continental scale.

• Balloon Soundings with COBALD ETH Zurich website
• LOAC website Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (Orleans)
• Optical fluorescent hygrosonde for balloon sounding (FLASH-B) Central Aerological Observatory (CAO) website
• TRO-pico campaign website University of Reims Champagne Ardenne