iPhone goes to out sea: Testing the iPhone GPS receiver for locating and tracking autonomous underwater vehicles
One of the key components of the Autonomous Underwater Explorers (AUEs) currently under development in our lab is a GPS receiver for locating, tracking, and recovering the AUEs after a deployment. Because the AUEs will be floating right at the surface of the water, there are problems acquiring satellites and getting reliable GPS fixes using conventional receivers.On a recent cruise, we had the opportunity to test the GPS receiver of the iPhone 3G. The test consisted of putting together a small plastic housing for the iPhone that was weighted to ensure the iPhone was at the surface. Below is a photograph of the components of the housing:GPSVisualizer, we obtained a nice GPS track:link to explore the GPS track intertactively on EveryTrail.comNote that this was recorded by the iPhone while it was partially underwater, bobbing up and down as it was towed behind a ship!Many GPS receivers fail to work at all when used right at the surface of the ocean. Yet the iPhone not only worked, it worked well! There are several factors to this performance. Perhaps one of the most significant is that the iPhone uses the cellular network to acquire GPS almanacs and therefore can rapidly initialize and start computing GPS coordinates. Of course without the cellular network, this performance would be reduced, but none the less, the iPhone does provide a solution for acquiring GPS fixes at the surface (perhaps even slightly under water) of the ocean!