טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentRokhlin Vadim
SubjectAttitude Determination by Means of Dual Frequency GPS
Receivers
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Gilad Even-Tzur
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract


In many civil and military systems finding direction with high accuracy is of top importance. GPS Attitude Determination (AD) is used in machine control and guidance to aid the system in initializing process. Some instruments such as a compass or a gyroscope are useful yet inherently limited. A ?magnetic compass determines direction relative to the magnetic north. It cannot be used in magnetically induced areas. A Gyroscope accumulates errors due ?to drifts, thus, requiring periodic recalibrations.?

Global navigation satellite systems like GPS allows for additional ways of attitude determination. It operates 24 hour a day ?and is not prone to any of the mentioned limitations except an open sky.?

In order to achieve precise attitude determination one can use GPS carrier phase observations ?with correctly resolved integer cycle ambiguities.? In integrated multiple GPS antenna attitude systems, double difference carrier phase observables are used in order to annul the atmospheric and hardware errors (receiver and satellite)?. The idea of attitude determination is, first of all, to calculate baseline between the antennas using differential position and then to calculate attitude parameters. Calculation of the integer ambiguity and attitude parameters are solved by least squares method.

When data collected by single frequency receiver, the initializing of the attitude determination system takes up to 10 minutes with correctly resolved integer ambiguity. This research examines the influence of additional frequency L2 added to L1 and its impact on duration of initialization time and precision of the solution. According to the research results, dual frequency data significantly shorten time of initialization but do not have any influence on accuracy of the solution.

The speed of the integer ambiguities solution depends on changes in the receiver-satellite geometry, thus we ?implement an antenna rotation algorithm, in order to speed up the geometrical change.? Baseline rotation method is designed to faster geometry change. According to the research results rotation antenna technique shortens initialization by single frequency receiver data without influencing the data collected by dual frequency receiver.