Toufic-Michel Hawat Lab. de Physique Molecular et Applicationssis (Lebanon) Claude Camy-Peyret LPMA/Univ. Pierre et Marie Curie (France) Roger J. Torguet Inst. d'Electronique/Micro-electronique (France)
A heliostat is designed and built to track the sun for optical remote sensing of the stratosphere from a balloon-borne pointed gondola. The tracking mechanism is controlled by two direct torque motors used to drive a single flat acquisition mirror. A horizontal turntable, rigidly attached to the azimuth drive, supports the elevation assembly. A position sensor receiving a small part of the solar beam reflected off the main acquisition mirror is used for fine servo control. Using a CCD camera prepointing of the acquisition mirror is achieved when the sun is in the field of view of the heliostat. This system is coupled with a high- resolution (0.02-cm-1) Fourier transform IR (FTIR) spectrometer to retrieve stratospheric trace species concentration profiles. The suntracker directs the solar radiation in a stable direction along the spectrometer optical axis. The pointing precision is 1 arcmin from a stratospheric gondola, which has static and dynamic angular excursions up to 6 deg. The heliostat coupled to the Limb Profile Monitor of the Atmosphere (LPMA) instrument performs successfully on several balloon flights. The description, ground tests, and balloon flight results of the suntracker are presented.