Description of the payload
It is an advanced Fourier Transform Infra Red (FTIR) spectrometer specially tailored to the operation on a stratospheric balloon gondola. It allows precise limb emission sounding of chemical constituents related to the stratospheric ozone problem and the greenhouse effect. This method is appropriate to obtain vertical profiles of ozone and a considerable number of key radicals (NO, NO2), reservoir species (HNO3, N2O5, ClONO2, and HO2NO2) as well as source gases (CH4, N2O, H2O, CFC-11, CFC-12, CFC-22, CCl4, CF4, C2H6, and SF6) simultaneously, with an altitude resolution of 2 to 3 km.
The MIPAS-B experiment was also thought as precursor for a space version of MIPAS actually installed onboard ENVISAT.
The instrument is divided in five operational segments:
(1) the gondola,
(2) the line-of-sight (LOS) stabilization and reference system,
(3) the cryogenic spectrometer,
(4) the on-board electronics, and
(5) the ground control equipment
The gondola is a frame construction, developed by the Geneva Observatory, combining high stability and safety with relatively low weight and easy servicing.
The LOS system is based on a miniaturized inertial navigation system with embedded GPS (Global Positioning System) that provides the attitude and heading reference of the instrument frame needed for the control loop to maintain the LOS within 300 m at the tangent point. A CCD star camera takes images of stars in the direction of the LOS that are used as absolute reference.
The spectrometer consists of a three-mirror off-axis telescope, a double-pendulum interferometer, and a four channel liquid-He cooled infrared detector system. The heart of the instrument is the double pendulum interferometer, a modification of the classical Michelson set-up. The four-channel detector system allows the simultaneous coverage of the most important absorption bands of ozone-relevant molecules between 5.2 and 13.3 µm.
The analogue data is sampled on-board, mixed with the information of the other channels and the housekeeping data, and sent to ground via telemetry at a data rate of 250 kbit/s. An uplink connection of 1200 bit/s ensures full commandability of the instrument during flight.
On ground, the raw data is split up again and stored immediately in a data base. At the same time, housekeeping data and interferograms can be viewed and processed to allow on-line evaluation of measured data and of instrumental health.
Details of the balloon flight and scientific outcome
Launch site: Domingos Rego Aerodrome, Timón, Maranhao, Brazil
Balloon launched by: Centre National d'Etudes Spatiales (CNES)
Balloon manufacturer/size/composition: Zero Pressure Balloon model 400z Zodiac - 400.000 m3
Campaign: SCOUT 2008
Payload weight: 720 kgs
The balloon was launched by auxilliary balloon method at 22:23 local time on June 5, 2008.
The flight profile was managed perfectly by CNES team in close cooperation with the MIPAS principal investigator, taking advantage of the QBO wind system and the sunrise, allowing for a flight including several hours of observations at nigh-time, the transition period around sunrise and about 8 hours during day time.
The payload was separated from the balloon shortly before sunset on June 6 landing in the dense rain forest near Gonçalves Dias, Maranhao state. The recovery team needed to cut 35 trees before being able to recover the gondola and the flight train.
This was the flight # 16 of MIPAS-B2 and the second one to be carried out in the Tropics.
As piggy back payloads were included two others instruments in the gondola. TELIS (Terahertz and Submillimeter Limb Sounder) a 3 channel cryogenic heterodyne receiver developed by DLR with high sensitivity and stability, which like MIPAS is a limb sounder measuring reactive species, water isotopomers and some atmospheric tracers with a vertical resolution of about 2 km. The second one was mini-DOAS (OSAKAR) developed by the IUP Heidelberg, a two channel automated UV/vis Limb scanning spectrometer created to measure measure time dependent profiles of UV/vis absorbing atmospheric radicals.
The MIPAS-B instrument showed excellent performance. Data was acquired from about 23:00 local time until 14:00 local time of the following day. The observations started with a 3-D cloud survey followed by validation measurements of MIPAS on Envisat. The spatial coincidence was better than 100 km. In addition measurements were taken which match trajectories of SCIAMACHY and GOMOS and an MLS overpass. After the validation tasks, were performed several observations including measurements of convective outflow, deep convection, shallow convection and background TTL, sunrise sequences for the measurement of short-lived species as well as Nadir measurements.
TELIS experimented during ascent colder temperatures than expected causing a malfunction in the steering mechanism of the instrument limiting the angular range of observations to down looking ranges of 10 to 20 degrees. Therefore, no limb sounding and no deep space view for calibration could be done.
Finally, the measurements of both mini-DOAS's spectrometers started at ground but due to a malfunction of the computer the higher resolution instrument failed shortly after take-off. Therefore, only measurements of the lower resolving instrument were performed.
External references and bibliographical sources