As of yesterday, we (mostly) finished the the install of our equipment on the P-3 in preparation for our flights in Alaska. We sucessfully tested the GPS rack, the INS, ATM2, ATM3, and (the new) ATM4. For a brief description of what our equipment does, read on…

The position of the plane is recorded using our Ashtec Z-12 gps receivers (of which we use four for redundancy). With the combination of additional ground receivers, we are able to compute the trajectory of the plane to a very high accuracy, even over long distances. Of course, a lot of work is involved in error reduction to get the best trajectory possible, and I don’t know a whole about the details.

We have a Navigation rack on the plane that shows the pilots where we would like to fly, with pre-defined flight lines that are created with some kind of science work in mind – flying over a glacier or a beach, for example.

The ATM racks (Airborne Topographic Mapper) are used to scan a surface with a laser and get a range from the position of the plane to the ground. Since the position of the plane is known (GPS), and the orientation of the plane is known (INS), the range computed can be translated into a surface elevation. Each ATM records ranges at 5000Hz and the laser is fired onto a rotating mirror which produces an ellipsoid-ish scan pattern on the ground.

ATM4 has been my project, and I have it in a prototype stage that will hopefully prove itself in Alaska. This system works differently than ATM3 or ATM2 in that it records waveforms, not ranges. In recording waveforms, the range can be computer more accurately than with the old hardware (ATM2 and 3), and more information can be found from the data. Trees, for example, will produce multiple returns from the laser pulse, and so we will be able to detect the top of the tree as well as the ground below, enabling us to know how tall the tree is and what the bare surface looks like below the tree. There are other uses, too, like determining water depth along beaches or coastlines and other things.

ATM4 also records surface temperature (using a radiometer), GPS (just a rough trajectory), and will be fitted to record INS data as well as other bits of information.