It's a reflector used to bounce sunlight onto the actors and fill in the light. This one's a "small" reflector (12x12 foot). In Hollywood productions they can go up to like 100 feet and are suspended from cranes!
One of my favorite angles on the location. DS9Sega pointed it out when we scouted and I was determined to use it somewhere.
The "favorite angle" Dennis mentioned is what the camera is pointed at in this pic. I'm at the upper right with the bullhorn calling out directions to the background players across what we called the "crater".
There's always a good reason to post a picture of Susan. Also, our gallant crew - from left to right that would be Carl Leonard, Doug Caprette, Maurice Molyneaux, Romel Punsal, Alex Ibrahim and Cynthia Lin.
"POLARIS. Brought to you by POLARIS ATVs. When you're lost on the edge of nowhere on a planet that can't exist, drive a POLARIS!"
What you don't see is the plastic and blankets on the ground that make it posisble for them to kneel on rocky terrain without ruining the costumes.