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The Visible Imaging System (VIS) is a set of three low-light-level
cameras to be flown on the POLAR spacecraft of the Global Geospace
Science (GGS) program which is an element of the International
Solar-Terrestrial Physics (ISTP) campaign. Two of these cameras share
primary and some secondary optics and are designed to provide images of
the night-time auroral oval at visible wavelengths. A third camera is
used to monitor the directions of the fields-of-view of these sensitive
auroral cameras with respect to sunlit Earth. The auroral emissions of
interest include those from N2+ at
391.4 nm, OI at 557.7 and 630.0 nm, HI at 656.3 nm, and OII at 732.0 nm.
The two auroral cameras have different spatial resolutions. These
resolutions are about 10 km and 20 km from a spacecraft altitude of 8
Re. The time to acquire and telemeter a 256 × 256-pixel image is about 12
s. The primary scientific objectives of this imaging instrumentation,
together with the in situ observations from the ensemble of ISTP
spacecraft, are (1) quantitative assessment of the dissipation of
magnetospheric energy into the auroral ionosphere, (2) an instantaneous
reference system for the in situ measurements, (3) development of
a substantial model for energy flow within the magnetosphere, (4)
investigation of the topology of the magnetosphere, and (5) delineation
of the responses of the magnetosphere to substorms and variable solar
wind conditions.