MER CALIBRATION TARGET
In 2003, NASA launched twin rovers (the Mars Exploration Rovers or MER) to Mars. Named Spirit and Opportunity, they arrived in early 2004 and spent the next decade providing a treasure trove of data for scientists. As of early 2018, the Opportunity Rover is still going!
On each rover is a calibration target (see photo below) that's always visible to
the main camera (PANCAM). The purpose of the target is to act as a reference of
color and brightness so scientists can make accurate measurements of the true
surface color and brightness. I was asked by Jim Bell (MER PANCAM team) to use the BUG
lab to measure the bi-directional reflectance distribution function (BRDF) of materials used in the MER calibration target. The
BUG lab is ideally suited to do this since it can measure the full BRDF of a
material in a short period of time. There are 7 different colored target
materials (black, gray, red, green, yellow, blue, white) and 11 different PANCAM
filters, ranging from 430nm to 990nm. Jim had a special adapter machined so that
we could use the PANCAM flight spare filter set when making the measurements.
Each set of measurements took approximately 20 min, so the entire suite of
filters and targets took a total of nearly 30 hrs of measurement time, spread
over a several week period.
In the photo below, I'm holding the engineering model for the calibration