ISIS-II Scanning Auroral Photometer.

The ISIS-II dual wavelength scanning auroral photometer is designed to map the distribution of auroral emissions at 5577 A and 3914 A over the portion of the dark earth visible to the spacecraft. A combination of internal electronic scanning and the natural orbital and rotational motions of the spacecraft causes a dual wavelength photometer to be scanned systematically across the earth. The data will be reproduced directly in the form of separate pictures representing emissions at each wavelength, which will be used to study the large-scale distribution and morphology of auroras, to study the ratio of 3914-A and 5577-A emissions thought to depend upon the energies of exciting particles), and to compare with results from other instruments on board the spacecraft and on the ground. The Red Line Photometer experiment on the same spacecraft is described in an accompanying paper by Shepherd et al. [Appl. Opt. 12, 1767 (1973)]. The instrument can be thought of as the photometric equivalent of an all-sky color camera which will view the aurora from above instead of below and with a much wider vantage point unobstructed by cloud and haze. In one satellite pass, the instrument will be capable of surveying (in one hemisphere) the entire polar region in which auroras normally occur.

ISIS-II Atomic Oxygen Red Line Photometer.

One of the new features of the ISIS-II spacecraft, fourth in the Alouette/ISIS series, is the inclusion of two optical instruments. The scanning auroral photometer is described by Anger et al. in a companion paper [Appl. Opt. 12, 1753 (1973)]. The red line photometer described here is similar in concept; it is designed to map the global distribution of the 01 6300-A emission with a spatial resolution of about 100 km, a measurement accuracy of 10%, and a detection threshold of 10 R. The objective is to delineate the various processes leading to the excitation of O((1)D) in the airglow and aurora by observing the global variation and by comparison with data from other instruments on board the same spacecraft. The device is now operating successfully in orbit, and detailed orbital performance characteristics will appear in a later publication.