Hello, my name is Jan Van Sickle and I would like to welcome you to the GPS course. The first image here is a representation of the Block II/IIA/IIR/IIR-M satellites that make up the majority of the current constellation of GPS satellites. In this first lesson, we will be talking about the GPS signal. I think it is a good place to begin, because it gives you a general idea of how GPS functions, how positions are derived from the system. This capability, of course, is at the heart of the application of GPS to various components.