A stereoscopic imaging method for measuring the altitude of the near infrared airglow layer

A program for determining the altitude of the barycenter of the near-infrared emissive layer at the mesopause level has been undertaken. The objective is to measure the two geometric parameters of the emissive layer: its altitude and thickness in order to correlate these values with the parameters of the dynamic processes that propagate at those altitudes. A first set of correlated observations was obtained in September 2000. Two cameras were set in simultaneous operation at Pic du Midi Observatory (Hautes-Pyrénées, altitude 2860 m) and at Pic de Château-Renard (Hautes-Alpes, altitude 2989 m). The azimuths of the lines of sight were opposite along the line that joined the two observation points. The star images were removed using a numerical filter. Then the perspective inversion method developed by Pautet (Applied Optics 41, 823-831, 2002) was used to provide images of the emissive layer as seen by a virtual camera located vertically above the observation sites. The intensity correlation coefficient is computed for matched pixel blocks. The results for the night of September 8-9, 2000 will be presented. In the region where the fields of view of the cameras superimpose, the altitude for the maximum of the airglow intensity is 87.3 km. This value is the mean value for the altitude determinations. The median value is the same: 87.3 km. The emissive layer profile is retrieved with a height resolution of 0.2 km. The layer is located between the extreme altitudes of 85.4 and 89.9 km. A 2D chart representing the altitude of the layer barycenter is compared with a 2D representation of the emission intensity. In conclusion, a precise method for retrieving the near-IR airglow layer altitude with a precision of 0.2 km has been developed and will be used for measuring the altitude of the layer barycenter at different points of the wave field.