PVO VENUS ONMS BROWSE SUPERTHERMAL OXYGEN 12 SECOND V1.0

These ions were observed in early orbitsduring measurements of the neutral density near periapsis, havean erratic and unpredictable signature, and occur at too high analtitude to be due to the neutral atmosphere. When the altitudeof periapsis increased above the point where sensible neutraldensity measurements could be made, the instrument was configuredspecifically to detect superthermal ions.

In general, for orbitnumbers 1 to 645, data were taken from the RPA mode. The gasbackground signal with the filament on is about a factor of 10less in this mode than in non-RPA mode, resulting in a lowerdetection threshold. For orbit numbers above 923, the instrumentwas deliberately configured with the filament off and non-RPAmode data was used.