The sites are highly weather dependent.  Rocks may appear or disappear depending on the wind’s transportation of sand.  The sand dunes are typically at an angle of repose, making a robot’s direct approach to the transmitter very difficult.  The typical distance from the start to the finish is 50-m or less.  It is possible to change batteries between trials.  Shiny object in PICT0020.JPG is a yard stick.  Click on picture to enlarge.