Potential field based coordinates: -Astronomical latitude and longitude -Orthometric heights (heights measured about an equipotential surface, nominally mean-sea-level

GPS Observables Today's class we start discussing the nature of GPS observables and the methods used to make range and phase measurements Start with idea of remotely measuring distances

Examined methods for measuring distances Examined GPS codes that allow a type of distance measurement and phase to be measured Examine how the range measurements are defined Use of carrier phase measurements Examine rinEx format and look at some \raw data

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?

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

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

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

Mathematical models in GPS Review assignment dates (updated on class web page) Paper draft due Mon April 29 Homework 3 due Fri May 03 -Final class is Wed May 15. Oral presentations o papers. Each presentation should be 15-20 minutes, with additional time for questions. · Next three lectures:

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

Styles of kinematic GPS Kinematic GPS techniques go by a number of names with features that are often receiver specific Kinematic GPS: Early term which implies that there is no loss of lock while the receiver is moving. In survey mode, if loss of ock occurs the antenna must be returned to a point of know ocation