 |
 |
||
 |
|
||
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
||||||||
 |
Planetary News: Mars (2006)Mars Exploration Rover Opportunity Takes Advantage of Parking Spot to Perform Imaging TricksBy Emily LakdawallaJanuary 11, 2006 "When life hands you lemons," the old saying goes, "make lemonade." The Mars Exploration Rover Opportunity has not moved its wheels for 45 sols, as engineers on Earth continue to work on a solution to the problem that developed in Opportunity's robotic arm on sol 654. As a result, Opportunity's point of view on the surrounding terrain has not changed one bit during the same period of time. Although frustrating for those who prefer to use the rovers' mobility to roll to new places and new sites as often as possible, the forced stillness has given Opportunity's imaging team the time and power to acquire a uniquely deep data set on the landscape around the rover. As at any particularly interesting spot, Opportunity begins by acquiring a complete color panorama:
Such a panorama usually takes around a week to acquire and typically involves capturing one panorama's worth of pictures through each of four or five of the twelve filters with which the rovers' cameras are equipped to view the Martian landscape. Three filters are necessary to make a color panorama. An additional filter is necessary to make a stereo (3-D) panorama. With all the extra time at Erebus, the Pancam team continued sequencing more complete panoramas through more filters. In the end, more than 1,300 images had been acquired through all twelve multispectral filters on the cameras, making the Erebus panorama the most data-rich one acquired by either of the rovers throughout the entire mission. Was the 12-filter panorama done for scientific value or just because it was there? The answer is "a little of both," according to Pancam Payload Element Lead Jim Bell. "We certainly had the opportunity! But whenever we do all these different filter measurements, we maximize our sensitivity to compositional differences from region to region."
In particular, Bell explained, at Opportunity's landing site the compositional differences are carried within the "blueberries" or hematite concretions that litter the ground. But blueberries are small things and can only be resolved in the foreground of an image, close to the rover. "Once you get out of the resolution range where Pancam can detect blueberries, you can't see them in pictures. But you can deduce their presence at a distance, and it works better the more filters you add," especially with the addition of more of the near-infrared filters in the rover's right eye. "It's also the case that [with more filters] we increase our sensitivity to variations in the basaltic minerals. Pancam is not Mini-TES -- we can't do compositional mapping -- but we can put constraints on those kinds of things." Another experiment that the Pancam team has been performing is to take many images of the same interesting outcrop at different times of day. As the Sun moves across the sky, it outlines different textural features in the outcrops with patterns of light and shadow. The rover has certainly acquired images of outcrops at different times of day before, but the imaging team rarely has the opportunity to pick and choose times of day for imaging. "You never really know [what time of day] you're going to get the best textural information because it's so strongly a function of the texture and how it's oriented relative to the Sun. Previously we've taken our chances, but here we had the chance to sample a whole bunch of times of day," Bell said. The Pancam team struck gold with this particular imaging experiment. One particular late afternoon image of the outcrop called "Overgaard" in front of Opportunity contained "the best shallow-water sedimentary features we've seen in the entire mission," Bell remarked. The features are called "festoon" structures, upwardly-concave, nested sedimentary beds that form as sand ripples propagate across the bed of a shallow body of moving water. So although Opportunity's forced rest has prevented it from further progress toward Victoria Crater, the time hasn't been wasted. Bell, for one, is extremely grateful that if Opportunity had to be stuck, it was stuck at such an interesting site. For comparison, Opportunity's last break in progress was at a site so singularly monotonous that the panorama the rover acquired there was named "Rub Al Khali" after the Empty Quarter of the Saudi Arabian desert. By contrast, Erebus is so interesting that "when we do move, we're not going to move very far," Bell said. "We're going to use the Microscopic Imager to really nail those festoon structures." |
|||||||||
 |
 |
|||||||||
[ what is this? ]