Re: Mars Pathfinder Stereo Camera...

[P3D John Ohrt <johrt@xxxxxxx>]

P3D Dr. George A. Themelis wrote:
> Is that a fancy description of anaglyph?

> I am lost here... What are stereo filters?  If these are colored
> filters for anaglyph images how come they are combined with the
> geologic filters?

I haven't been following the program that closely but I am familiar with
that style of design.  There are two separate optical paths imaged onto
different areas of the same CCD.  Each path has a 12 position filter
wheel.  Six filters are paired so there are six slots left in each
wheel.  Six slots in one wheel and five slots in the other wheel are
occupied with geological filters.  The last slot is a lens to provide a
closeup capability.

Since the system is a parallel view system, then is no need for for
anaglyph filters at the camera, but of course that doesn't mean you
couldn't use an anaglyph presentation at the display.

The stereo baseline is only 80 cm so I can't understand why the
atmospheric filters are paired unless the pairing permits the filters to
be subtly different.  In atmospheric work, it is sometimes desireable to
measure the narrowband intensity versus and extremely narrow band
intensity.  This permits you to better identify the intensity of a
single emission line from the broad band phenomena.  This is a pretty
basic capability though, and there may be more sophisitated science in
play than I am aware of.  (I used to provide the instrument, not do the
science.)

The CCD is controlled as a frame transfer device where one half of the
ccd is masked.  This permits you to send a rapid burst of 256 clocks to
move the current image under the mask where it can be readout at
leasure.  This technology is effectively an electronic shutter and
depending on ccd characteristics, exposures less than 1/1000 sec can be
used with extremely high precision and repeatability.  Much better than
mechanical shutters which are very failure prone, relatively speaking.

eg. The Wind Imaging Interferometer launched in September, 1991 uses an
identical basic design (dual-field frame transfer) and has been taking
images every 2 seconds or so since then and keeps right on ticking. 
Although a combined Canada(lead)/NASA/France experiment, the camera is
Canadian.  Guess that's why it wasn't mentioned :-)

Seriously, JPL among others were quite open with camera design
techniques and very helpful.  At the time, JPL had previously used the
same RCA device we were using and we were able to meet "frying ant"
qualification based on their tests.

The "frying ant" qualification confirms that the camera can survive an
indefinite exposure to full sun with the aperture wide open.

I'll try to find out more, but even last night any NASA site with Mars
info was paralyzed when I checked.

Regards,
--
John Ohrt,  Regina, SK, Canada
johrt@xxxxxxx


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