Balloon-borne optical spectrometer

• Institut für Umweltphysik (IUP), University of Heidelberg, Germany

The research at IUP-Heidelberg addresses the composition, photochemistry, and climate of the lower (troposphere) and middle atmosphere (stratosphere).

A particular focus of research involves the deployment of optical spectrometers on research aircraft, balloons and satellites.

In this context, a novel mini-DOAS (Differential Optical Absorption Spectrometer, size (260×260×310 mm³) has been designed for low weight (<7 kg) and low power consumption (7.5 W), necessary in automated balloon-borne measurements. Here, a particular emphasis has been put on stable optical imaging and large signal to noise ratio for light detection, features found to be necessary for the detection of low abundant UV/vis absorbing atmospheric trace gases (Ozone, NO2, BrO, OClO, IO, O4, H2O).
The dual channel mini-DOAS instrument consists of 5 major parts:

1. light intake telescopes
2. glass fibre bundles which conduct the skylight from the telescopes into the spectrometers
3. optical spectrometers
4. evacuated and temperature stabilized housing
5. single board computer for data handling and storage.

Data handling and storage of the mini-DOAS instrument is performed by a single board PC (Cool RoadRunner II with AMD Geode GX1 at 200MHz) which is equipped with a flash memory card. The allocated data are transferred from the spectrometers to the PC via a USB data transfer connection, which allows a data transmission rate fast enough to record single optical spectra every 25 ms (Data rate 1.5 MB/s). The PC can alternatively be operated under the operational systems Windows or Linux using lab-owned DOASIS or XDOAS software packages, respectively. Both software tools support the automatic adjustment of the signal integration time, the recording and storage of the measured spectra and the control of a limb scanning stepper motor.

As of July 2005, the mini-DOAS instrument has already been successfully deployed on 8 stratospheric flights performed from several launch sites ranging from the arctic to the tropics. During such applications the ambient conditions may considerably vary, from +40°C to -40°C encountered at the ground (p = 1023 mbar), to -80°C in the lowermost stratosphere (10 - 20 km, p = 70 - 200 mbar), and -20°C at maximum flight altitude (39 km, or p = 3 mbar). This variety of ambient conditions evidently stresses the mechanical and electronic components of the instrument.

A detailed description of the instrument can be found at:
http://www.copernicus.org/EGU/acp/acp/5/1409/acp-5-1409.pdf
and information about the IUP research at:
http://www.iup.uni-heidelberg.de/institut/forschung

• back