  The `Cyborg Astrobiologist' (CA) has undergone a second geological field
trial, at a red sandstone site in northern Guadalajara, Spain, near Riba de
Santiuste. The Cyborg Astrobiologist is a wearable computer and video camera
system that has demonstrated a capability to find uncommon interest points in
geological imagery in real-time in the field. The first (of three) geological
structures that we studied was an outcrop of nearly homogeneous sandstone,
which exhibits oxidized-iron impurities in red and and an absence of these iron
impurities in white. The white areas in these ``red beds'' have turned white
because the iron has been removed by chemical reduction, perhaps by a
biological agent. The computer vision system found in one instance several
(iron-free) white spots to be uncommon and therefore interesting, as well as
several small and dark nodules. The second geological structure contained
white, textured mineral deposits on the surface of the sandstone, which were
found by the CA to be interesting. The third geological structure was a 50 cm
thick paleosol layer, with fossilized root structures of some plants, which
were found by the CA to be interesting. A quasi-blind comparison of the Cyborg
Astrobiologist's interest points for these images with the interest points
determined afterwards by a human geologist shows that the Cyborg Astrobiologist
concurred with the human geologist 68% of the time (true positive rate), with a
32% false positive rate and a 32% false negative rate.
  (abstract has been abridged).
