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began to play with the contrast, blowing up first one part of the scene and
then another. With contrast enhancement, and false color, he could separate
various temperatures. Chartreuse equaled everything warmer than ten degrees
above the average of the pictures; dull brown equaled everything else.
Nothing. Then a step up.
Chartreuse equaling everything more than five degrees above average. Still
nothing. An active buggy, warmed by its heaters, would have been a blazing
beacon with high enough resolution, but at this scale it was too small to be
seen, a candle floating in the ocean at night, viewed from ten kilometers up.
Carter's arsenal of techniques went beyond analysis of single images. As a
long shot, he looked at differences between images preceding Stafford's trip
and following it. The method was simple enough.
Registering the pixels at four corners of a latitude-longitude grid around the
crater, he could subtract one rectified picture from another. This produced an
image that registered strong tones only in areas that had changed between the
date of the first image and the second. If nothing had changed, the result was
a featureless gray. There was a correction for sun angle, but if the sun was
at substantially different angles, the resulting image would show a pattern
corresponding to changing shadows. He had already used this technique on the
high-res visible-light photos that bracketed Stafford's trip. It simply
revealed spidery traces of the buggy tracks that he'd discovered at Mars City
and used to track Stafford on the ground.
Carter didn't know what this technique might yield in the thermal infrared,
but he needed all the ploys he could get.
The difference picture, 44 Feb minus 39 Feb, two kilometers on a side flashed
quietly onto the screen.
False color thermal infrared of a square, two kilometers on a side, centered
on the crater. There was nothing. The image was frustratingly gray. Both
pictures had been taken at night. The temperatures must have been similar
everywhere.
He called up a contrast stretch and the screen obediently created a revised
version of the picture that broke up into a garish chartreuse-and-brown
pattern that appeared to be random noise. And yet...
Southwest of the crater, a few hundred meters out on the plain, was a patch of
light. Was it more noise?
No. It persisted even when he changed the temperature limits and reduced the
stretch coefficient. It stood out from the noise. There had been warmth there
on the forty-fourth that was not there on the thirty-ninth.
What the hell did that mean?
A warm patch that had not been there a few days earlier. He expanded the
scale. The picture broke up into a grid of pixels. The warm spot had
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structure. The central pixel was the brightest pixel in the frame. It was
surrounded by a target ring of slightly less bright pixels, and an outer ring
of still fainter ones that nearly blended with the background. The whole thing
was perhaps thirty meters across, relatively circular. A round spot warmest at
the center; at night. There was nothing else like it in the frame.
Fumbling with the disks, trying to beat the library's closing hour, he went
back to the high-resolution visual at visible wavelengths. Here, the dark
rocks and light dunes appeared in their ordinary sunlit colors.
The region of the warm spot was unusually smooth, free of rocks, but there was
nothing extraordinary in the picture possibly a darker smudge in the
questionable spot in the views made after Feb 43, but nothing to fecundate a
theory.
Carter sat, staring at the picture and at the cluttered desk.
"I'm sorry, it's closing time." It was the librarian, standing in the cubicle
entrance behind him. "Have you found what you're looking for?"
"I don't know. Maybe I'm on the track of something."
"Good." A professional smile. She left.
Carter regretted the awkwardness with her the day before, when he had checked
in. He could have liked her, he thought. Librarian on Phobos. Interesting [ Pobierz całość w formacie PDF ]