Basic concepts Basic problem: We measure range and phase data that are related to the positions of the ground receiver, satellites and other quantities How do we determine the \ best position for the receiver and other quantities What do we mean by best \ estimate?
Propagation Basics: - Signal, tagged with time from satellite clock, transmitted. - About66msec(20,000km) later the signal arrives at GPS receiver. Satellite has moved about 66 m during the time it takes signal to propagate to receiver
Basic antenna operation Receiving and transmitting antennas are identical: Time just flows in opposite directions. Antenna problems are solved knowing the current distribution J(x') in the antenna and using a vector potential
GPS Groups/Gs There are many international and national groups involved in the deployment of GPS The international organization is the International GPs Service(IGs)
Network Development of Network First measurements made in July 1992; just after start of International GPS Serviceigs). Since then measurements each year and often multiple campaigns per year. -The current network has over 1000 sites, many of them being recovery marks for the main
Primary research programs Geophysical research GPS analysis packages GAMIT (GPS at MIT): Uses double differences GYPSY: Jet Propulsion Laboratory (JPL) processing packages: Uses one-way observables and explicitly estimates clocks Bernese: Developed at Astronomical Institute
Propagation: lonospheric delay Summary -Quick review/introduction to propagating waves -Effects of low density plasma Additional effects -Treatment of ionospheric delay in GPS processing -Examples of some results
Specific common processes White-noise: Autocorrelation is Dirac-delta function; PSD is flat; integral of power under PSD is variance of process(true in general) First-order Gauss-Markov process (one of most models common in Kalman filtering)
Estimation · Summary Examine correlations -Process noise · White noise · Random walk First-order Gauss Markov Processes Kalman filters Estimation in which the parameters to be estimated are changing with time
