WINDII Instrument Description

WINDII is fundamentally a CCD camera, directed towards the earth's limb, with the bottom of the image at about 80 km and the top near 300 km above the earth's surface. There are two fields of view, one placed azimuthally 45 degrees away from the spacecraft velocity vector and the other 135 degrees away, providing vector winds along a track off to one side of the spacecraft. A Michelson interferometer placed in the optical path is stepped in optical path difference as a sequence of images is acquired. Since the Michelson output corresponding to a narrow line is a cosinusoid as the path difference is stepped, each pixel provides a cosinusoid in intensity whose phase gives the wind velocity for that pixel and whose modulation depth gives the atmospheric temperature.

The uniqueness of WINDII resides in the Michelson interferometer, a solid assembly of cemented glasses which form a rugged, achromatic and thermally compensated unit. The highly demanding fabrication was accomplished by Jeff Wimperis of Interoptics, with beamsplitter coatings designed by George Dobrowolski of NRC, and imaging lenses designed by Ian Powell of NRC that were fabricated at Leitz in Midland, Ontario. AIT (Advanced Information Technologies) Corporation was the prime contractor responsible for the provision of the entire system, working under contract to the CSA, and CAL Corporation was the principal subcontractor responsible for the execution of the flight unit.

The performance of WINDII in orbit has exceeded all expectations. It is extremely stable, very sensitive, and is providing wind measurements that exceed the design goal of 10 metres per second. Because of the variety of emissions viewed, an excellent baffle which permits viewing day and night, and a very good calibration system including a Helium-Neon laser (both provided by France), the quality and coverage far surpass any previous optical measurements made of this region. The dataset of more than 25 million images provides a baseline description of the upper atmosphere that will be studied for decades, as no equivalent successor is in sight.

WINDII being integrated to the Upper Atmosphere Research Spacecraft

Solar Terrestrial Physics Laboratory

Last update: February 23, 2000 by Alain Soltesz