Nine Image Mosaics for the DISR Archive

This directory contains large-scale image mosaics given here as nine
1250x1600 pixel images, centered on the Huygens landing site, with the
scale changing from one image to the next by a factor of two.

North is up, east is to the right.

The scales of the nine images are 0.5, 1, 2, 4, 8, 16, 32, 64, and 128
m/pixel.

Pixel number 1,1 is at the bottom left.  Following are the pixels of the
bottom row, etc.  Pixel number 625,800 is the same location in each
image.  It is the Huygens landing site, or at least within 50 m of the
landing site.

The files are in PPM format.  The first 20 bytes explain in ASCII the
file type, width, height, and maximum pixel value.  The rest of the file
lists each pixel value in 2-byte signed integers.

The data numbers divided by 666,666 give our best estimates of the
observed I/F, where I is the observed intensity, and pi*F is the solar
flux at the top of Titan's atmosphere.  The effective wavelength is about
770 nm.

Note that the resolution varies by large factors even on small scales,
since some areas were imaged from low altitudes while other nearby areas
were only imaged from 10 or 50 times higher altitudes.  The images of
highest resolutions were used to create the mosaic.  Where only low
resolution was available, the mosaic was left smooth.  Thus, regions
appearing to be smooth are typically regions imaged with poor resolution.

The geometry in these images is most reliable vetween 500 m and 5 km from
the landing site and unreliable more than 10 km away from the landing
site.  The photometric data is most reliable within 5 km of the landing
site and very unreliable more than 10 km from the landing site.