Using the HiRISE camera to take a special observation of a non-Mars target is a difficult but always interesting event for HiRISE Operations. While we have developed somewhat of a routine for regular imaging of the Martian surface, special observations require additional work that impacts our normal workflow as well as the science gathering of the other instruments onboard the Mars Reconnaissance Orbiter. Targeting specialists from Uplink already have so much work to do on a routine basis; adding in a special observation adds that much more work. Special observations are selected because they offer some scientific value that warrants the extra time, effort, and delay in routine science gathering.
We do not accept requests from the public directly regarding special observations. Our very knowledgeable science team determines months in advance that the right geometry for a unique observation of a non-Mars target with scientific value is coming up. Over several iterations between Uplink and the science team, the target is planned in detail. For a target like Deimos, the smaller and more distant moon of Mars, the spacecraft needs to slew away from Mars to point the camera correctly. This is a dance that requires coordination between HiRISE, the other instruments (who will generally not be observing during this period), and the MRO platform.
For this opportunity, we took two images of Deimos. The plan was to capture Deimos in the center of our CCD array so that the satellite would fall across our RED, BG, and IR color filters. Uplink did a fantastic job with their targeting! In the first observation – ESP_012065_9000 – Deimos lay across two channels of each color filter at the center of our array: RED4_0 and RED5_1, BG12_0 and BG13_1, and IR10_0 and IR11_1. In the second observation – ESP_012068_9000 – Deimos was fully contained within RED5_1, BG13_1, and IR11_1. You can find more information about these observations here.
What did it take for Downlink to put these images together? Well, Audrie and I came in on a Sunday (!) to wait for the observations. Then I spent some time putting together preliminary images to send out to the team. During the following week I worked on registering the color filters to create the false color images. See both images side by side here. Notice that green fringe around the first observation on the left? That is a bit of misregistration, something I could not seem to correct despite tweaking the position of the three color layers a pixel at a time. The first observation also required two separate stacks: (1) RED4_0, BG12_0, and IR10_0, and (2) RED5_1, BG13_1, and IR11_1. After registering the two sides separately, I stitched them together using an ISIS tool called hiccdstitch. That little notch you see at the top of the first observation is how the two sides almost but not quite line up. The two sides are slightly offset because their geometry is just slightly different.
Compared to the first observation, the second observation, confined to one channel each in the color filters, was wonderful to work with: no color balancing required, no stitching, and a relatively easy registration process!
GuyMac also helped make these Deimos observations a little easier to deal with than past special observations: he created a custom version of one of our processing pipelines that sharpens the image and brings out the colors a little bit. Once I had the observations registered, all I had to do was run them through his script for the really nice false color products you are now enjoying!