Instrument Information
IDENTIFIER urn:nasa:pds:context:instrument:pvo.ocpp::1.2
NAME Pioneer Venus Cloud Photopolarimeter
TYPE Polarimeter
DESCRIPTION The Cloud Photopolarimeter (OCPP) used a simplified version of the Imaging Photopolarimeter (IPP) flown on Pioneers 10 and 11 to provide low-resolution, four-color maps of the Venusian cloud cover with a high-resolution imaging capability near apocenter. The principal objective of this investigation was to determine the properties of the clouds and haze (both vertical and horizontal particle distribution), cloud particle size and refractive index, the cloud-top height, and the number density of particles. The instrument consists of a 3.7 cm Cassegrain telescope with a 15.7 cm focal length, backed by a 16 position filter wheel. The imaging mode has a 365-nm filter, a 0.4 x 0.45 mrad aperture field of view, and a single detector that feeds into the imaging channel. It can provide scan lines containing 1016 8-bit measurements of intensity (radiance), with a resolution of 30 km at the subspacecraft point. Approximately 3.5 hours are required to image the full planetary disk, or five full images in the roughly 18 hours of the orbit centered on apoapsis. The channel is sampled every 0.488 ms (0.610 ms low sample rate), absolute radiometric accuracy is 5%. The photopolarimetry mode uses four passband filters centered at 270 nm (far ultraviolet), 365 nm (ultraviolet), 550 nm (visible), and 935 nm (near infrared), with three half-wave retarder positions on the filter wheel for each of these. The field of view is 6.5 x 8 mrad, giving a resolution of 250 - 500 km at the subsatellite point. A Wollaston prism splits the output into two detectors, which are sampled simultaneously every 9.52 ms (28.6 ms low sample rate), with 11 bit a/d conversion, and an absolute radiometric accuracy of 5%. The limb-scan mode, used at the orbiter?s periapsis, uses a 690 nm filter with a 0.3 x 0.35 mrad field of view aperture and a single detector that feeds into the limb-scan channel, with a sampling every 0.310 ms (0.397 ms low sample rate) with 8 bit conversion, absolute radiometric accuracy is 5%. There is a calibration lamp for periodic calibration checks, which can view 0 to 145 degrees from the spacecraft spin axis by using the 5 rpm spin of the spacecraft. It uses a first in/first out 8192 bit memory (3072 bit section for photopolarimetry mode). The data format is 56 bits of status information followed by 8136 bits of data.
MODEL IDENTIFIER
NAIF INSTRUMENT IDENTIFIER
SERIAL NUMBER not applicable
REFERENCES Travis, L. D., et al., Orbiter cloud photopolarimeter investigation, Science, 203, No. 4382, 781-785, Feb. 1979.

Travis, L. D., et al., Cloud images from the Pioneer Venus Orbiter, Science, 205, No. 4401, 74-76, July 1979.

Rossow, W. B., et al., Cloud morphology and motions from Pioneer Venus images, J. Geophys. Res., 85, No. A13, 8107-8128, Dec. 1980.

Kawabata, K., et al., Cloud and haze properties from Pioneer Venus polarimetry, J. Geophys. Res., 85, No. A13, 8129-8140, Dec. 1980.