SPIRALE is a spectrometer with six tunable diode lasers dedicated to in situ measurements of trace compounds in the upper troposphere and the stratosphere up to 35 km altitude.
The 6 laser beams circulate in a multipass HERRIOTT cell located below the gondola. The lower mirror of the two-mirror cell is fixed at the top of a deployable mast. The distance between mirror is about 3.50 m. Given the curvature of the two identical mirrors, two stable optical configuration can be used : first 86 reflections and 300 m optical path, second 156 reflections and 554 m optical path, by moving the lower mirror 5 mm up.
The mast is deployed during the flight to have the first measurements at the tropopause. Around the instrument, a rigid metal frame encompasses it, in order to have a instrument-safe landing.
Inside the instrument, three liquid nitrogen cryostats, hold the six diode lasers and the 12 detectors.
Vertical profiles of concentrations of a great number of species like O3, CH4, CO, CO2, N2O, HNO3, NO2, NO, HCl, HOCl, H2O2, and COF2, are measured with a very high vertical resolution, a high sensitivity and a high precision.
Also was included in the gondola a piggy back experiment called STAC (Stratospheric and Tropospheric Aerosols Counter). It is an optical counter which can detect low particle concentrations, giving particle number densities and size distributions. Due to its small size, it can be mounted onboard various balloon-borne gondolas. The particles are drawn through a light beam emitted by a laser diode at 780 nm, and scattered light is received by a photodetector at a scattering angle of 70º. The number concentrations are calculated from the count rate of the photoelectric pulses received.
Launch site: European Space Range, Kiruna, Sweden
Balloon launched by: Centre National d'Etudes Spatiales (CNES)
Balloon manufacturer/size/composition: Zero Pressure Balloon
The balloon launch was successfully performed at 16:58 UT on January 20th 2006 by dynamic method assisted by an auxiliary balloon.
After reach float altitude of 27 km and a flight of 3.5 hours the balloon was taken down and the payload landed near the village of Lannavaara, in the north part of Sweden. The gondola structure was damaged during the landing without however affecting the instrument.
The recovery of the balloon and payload took place on 21 January by helicopter.
During this flight measurements were performed during the ascent of the balloon (from 10 to 27 km). This enabled the scientific team to measure simultaneously vertical profiles of O3, N2O, HNO3, and HCl mixing ratios and aerosols, with a very high vertical resolution of a few meters. Characteristic features of depletion linked to Polar Stratospheric Cloud formation were observed on the HCl and HNO3 profiles.