Astronomical observation through the NIR atmospheric emissive layer

International audienceThe emission of the upper atmosphere introduces an additional component into photometric observations of astronomical objects. In the I band for instance, the intensity of the atmospheric emission is of the order of 1 to 2 Imag20 per square arcsecond. The subtraction of this component is not easy because it varies during the night by as much as 50% and it is not homogeneous over the sky. A program aimed at understanding the main characteristics of the atmospheric emission was undertaken. A set of CCD images of the OH emission in the I band covering the sky was assembled in a panorama, it shows wide converging arches. An algorithm was developed in order to invert the perspective projection of the photographs. The result is a 2200 km wide view over Europe and Mediterranean Sea of the emission as seen from a virtual satellite. This image shows the presence of an extended wave field. A Fourier analysis allows to infer mean horizontal wavelength, mean temporal period and horizontal phase velocity. The atmospheric emission varies under the influence of atmospheric waves. A stereoscopic imaging program is currently under development to measure the amplitude and the energy of the atmospheric waves