[X] My Assistant

[GregM]

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[edstrick]

A number of postings back, somebody was "dissing" the Pioneer Spin-Scan Multi-Polariimiter/Camera as a primitive camera. I'd like to come, a bit, to it's defense.

The camera was actually 3 instruments in one. It was a zodiacal light photometer/polarimiter. On it's way out to Jupiter and beyond, it repeatedly imaged the entire sky except near the sun in red and blue light with full polarization analysis abilities. The resolution was terrible, about 1 or 1 1/2 degrees, but they were mapping the skyglow of the solarsystem, not taking pictures. They proved that the backscattered glow from the zodiacal light disappeared as you went through the asteroid belt to undetectably low levels, and proved that the gegenshein <counterglow--a bright patch in the zodiacal light centered on zero degree phase angle> was a photometric effect, and not due to a dust-cloud orbiting the sun at say the earth's L2 point.

Processing the zodiacal photometry stuff involved mapping the pixels onto the celestial sphere, identifying detectible stars in each field of view, and subtracting the calculated starlight to get sky maps free from bright star contamination. The team doing this work never produces sky-map images from the data, and I've always wanted to see color/polarization maps of the sky from the Pioneers.


The cameras also took intermediate resolution spin-scan polarimetry maps of Jupiter and Saturn with the disks well resolved at a full range of phase angles, not available from earth. Again, the images were 2 color, with full polarization analysys. This provided large amounts of QUANTITATIVE information on light scattering by cloud particles in the upper troposphere and stratosphere, data that was not duplicated or improved on in any way by the Voyagers. This data was and continues to be of use in modeling the structure of the visible parts of these planet's atmospheres.

Finally, the best images from Pioneer 10 had resolution approaching Voyager's best. Pioneer took a picture with 60 km/pixel <if I recall> resolution at closest approach. It''s reproduced in the Journal of Geophysical Research's Pioneer 10 special issue. Radiation hits caused the gain of the camera <basically exposure> to shift a few times during the sequence, and the data has a strong periodic noise component possibly associated with radiation hitting the spinning spacecraft, but it couild and should have been restored and composited into a color image. Voyager's best resolutions on Jupiter were only some 15 to 20 km.

[dvandorn]

A number of postings back, somebody was "dissing" the Pioneer Spin-Scan Multi-Polariimiter/Camera as a primitive camera.  I'd like to come, a bit, to it's defense....

Oh, I wasn't saying they didn't do some amazing things with that instrument. My point was (and remains) that it was not primarily an imaging system, and because of that, it was unable to take anything like the total number of pictures a dedicated imaging system would have, and, indeed, the highest resolution Pioneer images I've ever seen, though they may have similar theoretical resolution to Voyager images, all appeared to retain aberrations and "blurring" factors that made them appear far less clear than the average Voyager image.

I suppose it's possible that I have never seen properly corrected and cleaned-up Pioneer images -- do you have any links for high-quality versions? (Beg, beg...)

-the other Doug