The LPMA instrument (Limb Profile Monitor of the Atmosphere) is a high spectral resolution Fourier transform spectrometer operating in absorption against the sun. The objective is to record limb atmospheric spectra in selected intervals from the thermal infrared to the near-infrared.
The instrument is composed by a commercial BOMEM DA2 spectrometer customized for balloon operations. A specially designed two detectors output optics enables to cover simultaneously two spectral regions making it possible to sample simultaneously the two interferograms detected during the same scan of the moving mirror and allowing to collect information on atmospheric species absorbing in widely different spectral regions.
In order to reach a good signal to noise ratio spectra performance, the interferometer must be feeded with a stable solar beam exactly aligned along the optical axis of the instrument. To be able to do this, two sub-systems of the gondola are needed:
- a primary pointing system initially developed by the Observatory of Geneva for astronomical payloads, controling the azimuth of the gondola and maintaining the sun in the field of view of the instrument even during ascent in the dense layers of the upper troposphere or lower stratosphere where this is a rather difficult achievement.
- a suntracker (also known as a heliostat) developed in cooperation with the Institut d'Electronique el de Micro-electronique du Nord performing the fine pointing of the acquisition mirror through 2 axes servo-controlled gimbal compensating for the residual motions of the payload and maintaining a jitter of the solar beam direction at the input of the interferometer of less than 1 arc min.
In addition it is possible to accomodate on the gondola another instrument of the class 30-50 kg wich can benefit from their good pointing capabilities. In this flight also was part of the scientific payload onboard the gondola the DOAS (Differential Optical Absorption Spectroscopy) consisting of 2 light intake telescopes for simultaneous Nadir and scanning Limb observations (the latter being mounted on an automated elevation scanner). The incoming light is conducted into two Ocean Optics USB-2000 spectrometers which are mounted into an evacuated and thermo-stated housing and controlled by a single board computer for data handling and storage.
The instrument was created to help in the validation of the SCHIAMACHY instrument onboard ENVISAT.
Balloon launched on: 3/19/1998 at 16:02
Launch site: Virgen del Camino Airport, León, Spain
Balloon launched by: Centre National d'Etudes Spatiales (CNES)
Balloon manufacturer/size/composition: Zero Pressure Balloon model 402z 400.000 m3
Balloon serial number: 402z Nº 73
End of flight (L for landing time, W for last contact, otherwise termination time): 3/19/1998 at ~ 19:20
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 3 h 15 m
Payload weight: 979 kgs
Gondola weight: 595 kgs
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