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About Mars, the "Greenish" Planet.
| About Mars, the "Greenish" Planet. [message #33440] |
Sat, 04 January 2003 06:41 |
rgregoryclark
Messages: 1
Registered: January 2003
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Junior Member |
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I'm looking for the NASA PDS programs to perform the image corrections
described here:
"Images were acquired by the Viking Orbiters at approximately eight
second intervals. In this time
period, the viewing geometry changed enough so that the individual
images that make up the color set can not be properly registered
unless
the images are geometrically rectified. The brightness of pixels in an
image could be adjusted by choosing an exposure duration from a set of
values between 0.003 to 2.66 seconds. The brightness values could also
be adjusted by using a combination of three mode parameters: gain,
offset, and light flood. The gain parameter specified the sensitivity
of a VIS camera to light incident on the vidicon. There were two gain
settings: 'low' and 'high'. The high gain mode had twice the
sensitivity as the low gain mode. Thus, the low gain mode expanded the
dynamic range of the camera by 100%. The exposure duration and the
expected light level of a scene were the deciding factors for choosing
high or low gain modes for an imaging sequence."
And:
"(1) Viking Orbiter images can be radiometrically calibrated by
converting the digitized signal received from the camera (DN value)
into
a quantity that is proportional to the radiance reaching the sensor
[2, 3, 4]. Each Viking Orbiter VIS camera was calibrated before
flight.
In addition, changes in the calibration over time have been estimated
from analyses of images of deep space and dust storms. The radiometric
calibration procedure applies additive and multiplicative corrections
that account for the varying sensitivity of the vidicon across the
field of view and over time. The calibrated values are proportional to
radiance factor, which is defined as the ratio of the observed
radiance to the radiance of a normally illuminated lambertian
reflector of unit
reflectance at the same heliocentric distance.
(2) Geometric calibration of Viking Orbiter EDR images removes
electronic distortions and transforms the point perspective geometry
of the original image into a map projection [3, 4]. The electronic
distortions are barrel-shaped distortions from the electron beam
readout and complex distortions from interactions between the charge
on the vidicon face plate and the electron beam. The electronic
distortions are modeled by comparing the predicted locations of
undistorted reseau marks with the actual locations in an image."
From:
Archive of Digital Images
from NASA's Viking Orbiter 1 and 2 Missions
http://starbase.jpl.nasa.gov/pdsa_data/vo_1051/document/voli nfo.txt
It has to do with Viking orbiter color image composites such as this
one:
Topic: Re: Mars the "Greenish" Planet?
http://www.anomalies.net/ubb/ultimatebb.php?ubb=get_topic;f=25;t=004820
Bob Clark
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