Purpose of the flight and payload description
This flight transported two complementary instruments developed by the Laboratoire d'Optique Atmosphérique (LOA), Université des Sciences et Technologies de Lille in France.
BALLAD (BALloon Limb Aerosol Detection) was aimed at studying the scattering properties of the stratospheric aerosol by measuring the intensity (at 450, 600 and 850 nm) and the polarization (at 850 nm) of the Earth's limb, for a wide range of scattering angles. An inversion method of the radiances only, obtained in forward scattering, has been developped to retrieve the vertical profiles of the extinction coefficient and of an asymetry parameter of the aerosol. The objective of the instrument formed the Earth's limb image on a linear charge-coupled device (CCD) detector of 1728 pixels, the vertical FOV of the system was about 6°. A filter wheel, located between the objective and the detector, allowed multispectral radiance and polarization measurements to be performed. Two interference filters at 850 and 450 nm were dedicated to aerosol studies and a third channel centered at 600 nm was deployed for ozone detection. Three other filters centered at 850 nm were equipped with polaroids rotated by 60° with respect to one other to evaluate the linear degree of polarization of scattered light.
BALLAD was installed on board of the gondola with its optical axis, pointing approximately 2° below the balloon horizon. Combined with its large vertical FOV allowed observation of all the stratospheric layers, from the tropopause up to the balloon level, simultaneously with one exposure. The vertical resolution was about 350 m for a balloon ceiling at 30 km and a tangent height equal to 15 km. Measurements were carried out for solar elevation ranging from 2 to 10° and the rotation of the gondola around the vertical axis (1/3 rpm) permited BALLAD to observe Earth's limb for various azimuth angles (angular sampling 16°).
BOCCAD (Balloon OCCultation for Aerosol Detection) was built by LOA in 1994 to observe solar occultation through the atmosphere. It was planned to provide useful information for RADIBAL, and to provide a direct comparison with satellite measurements SAGE II and a POAM II. The objective formed the Sun's image on a CCD matrix of 244 by 550 pixels. The vertical and horizontal FOV of the instrument were 10° and 7.5° respectively. A filter wheel, located between the objective and the detector, allowed multispectral measurements to be performed. Three interference filters centered at 850, 780 and 443 nm were used for aerosol studies, and a fourth channel at 600 nm was dedicated to ozone detection. BOCCAD was installed on the same gondola as BALLAD and also operated at the balloon ceiling level. The gondola stoped rotating after the BALLAD measurements and the instrument pointed 2° below the balloon horizon so that the large FOV allowed observation of the whole occultation event. The measurements started when the solar elevation reached ca. 2° and the Sun's image could be obtained almost outside the atmosphere to provide a reference image in each channel. Typically about 300 images were formed successively in each channel during a sunset at high latitudes.
Details of the balloon flight
Balloon launched on: 10/12/1995 at 14:54 utc
Launch site: Centre de Lancement de Ballons CLBA, Aire Sur L'Adour, Landes, France
Balloon launched by: Centre National d'Etudes Spatiales (CNES)
Balloon manufacturer/size/composition: Zero Pressure Balloon model 50SF Zodiac - 50.000 m3
Balloon serial number: 50 SF Nº 3
End of flight (L for landing time, W for last contact, otherwise termination time): 10/12/1995 at ~ 18:00
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 3 h 2 m
Payload weight: 477 kgs
Gondola weight: 246 kgs