CONSIDERING THE IMPORTANCE OF GEOSYNCHRONOUS ORBIT (GEO), DIFFERENT COUNTRIES DEMAND TO SEND MORE SATELLITES TO THIS ORBIT THEREFORE NOWADAYS GEO IS BECOMING MORE AND MORE OCCUPIED AND CROWDED. THIS MATTER HIGHLIGHTS THE USAGE OF AN ACCURATE NAVIGATION SYSTEM FOR PREVENTING ANY COLLISION. AMONG DIFFERENT KINDS OF NAVIGATION SYSTEMS, DUE TO THEIR ACCURACY AND SIMPLICITY, GNSS AND SPECIALLY gps ARE AMONG THE MOST POPULAR NAVIGATION METHODS.IN THIS PAPER gps NAVIGATION DIFFICULTIES IN GEO IS EXPLAINED INCLUDING SIGNAL STRENGTH, VISIBILITY, DOPPLER AND DOPPLER RATE. THESE PARAMETERS ARE ESTIMATED FOR AN ARBITRARY GEO MISSION. IF THE RECEIVER IS ABLE TO TRACK WEAK SIGNALS, MOST OF PROBLEMS LIKE VISIBILITY AND DOP PARAMETERS CAN BE SOLVED. THE ESTIMATED PARAMETERS INDICATE THAT IF THE RECEIVER SIGNAL STRENGTH THRESHOLD IS ABOUT -29DBHZ, IT IS JUST ABLE TO TRACK MAIN-LOBE SIGNALS AND CAN NEVER TRACK 4 SATELLITES BUT IF ITS THRESHOLD IMPROVES TO ABOUT 14DBHZ IN 97% OF A DAY IT CAN TRACK AT LEAST 4 SATELLITES.IN THE NEXT PART OF THIS PAPER, VECTOR TRACKING METHOD ALONG WITH ITS PRINCIPLES AND PERFORMANCE ANALYSIS IS EXPLAINED. THE PERFORMANCE ANALYSIS PROVES THAT IT IS A SUITABLE TRACKING METHOD IN GEO MISSIONS AND CAN TRACK SIGNALS STRONGER THAN 13DBHZ.

RELATIVISTIC EFFECTS PLAY AN IMPORTANT ROLE IN THE PERFORMANCE OF THE GLOBAL POSITIONING SYSTEM (gps) AND IN WORLD-WIDE TIME COMPARISONS.THESE EFFECTS INCLUDE GRAVITATIONAL FREQUENCY SHIFTS, TIME DILATION AND SAGNAC EFFECT DUE TO EARTH ROTATION. IN THIS ARTICLE WE REVIEW SOME RELATIVISTIC EFFECTS INTRODUCED BY ASHBY AND CALCULATE THEM IN APPROXIMATE SOLUTION OF EINSTEIN’S FIELD EQUATIONS IN ISOTROPIC COORDINATES.

A gps-BASED METHOD IS PROPOSED WITHIN AN ITERATIVE PROCEDURE FOR ATTITUDE DETERMINATION OF THE MARINE PLATFORMS. AS THE CASES STUDY, A CRUISE CONDUCTED ON THE SURVEY VESSEL OF THE NATIONAL GEOGRAPHIC ORGANIZATION (NGO) OF IRAN, IN ORDER TO TEST THE EFFICIENCY OF THE METHOD. THREE ON-BOARD gps ANTENNAE WERE INSTALLED ON THE TEST VESSEL EQUIPPED WITH A MOTION REFERENCE UNIT (MRU) AS THE BENCHMARK. AS THE NUMERICAL RESULTS ASSERT THE CONSISTENCY BETWEEN THE gps-DERIVED AND MRU-MEASURED ATTITUDE ANGLES, THE PROPOSED METHOD IS RECOMMENDED FOR ATTITUDE DETERMINATION OF THE HYDROGRAPHIC VESSELS.

PLATE TECTONICS STUDIES USING gps REQUIRE PROPER ANALYSIS OF TIME SERIES, IN WHICH ALL FUNCTIONAL EFFECTS ARE UNDERSTOOD AND ALL STOCHASTIC EFFECTS ARE CAPTURED USING AN APPROPRIATE NOISE ASSESSMENT TECHNIQUE.BOTH ISSUES ARE ADDRESSED IN THIS CONTRIBUTION. AFTER APPLICATION OF A MULTIVARIATE OFFSET DETECTION METHOD, THE RESULTS OF TIME CORRELATED NOISE FOR A LARGE NUMBER OF Cgps STATIONS ARE PRESENTED. IT IS SHOWN THAT THE UNDETECTED OFFSETS CAN MIMIC RANDOM WALK NOISE, IN AGREEMENT WITH THE PREVIOUS WORK. RANDOM WALK NOISE WHICH WAS NOT CORRECTLY DETECTED IN CASE OF AN INEFFECTIVE OFFSET DETECTION METHOD RESULTED IN OBTAINING INCORRECT RATE UNCERTAINTIES. THIS ISSUE, IF NOT IMPLEMENTED CORRECTLY, WILL BIAS BOTH THE RATES AND THEIR UNCERTAINTIES. FURTHERMORE, APPLYING A NOISE ASSESSMENT METHOD INDICATES THAT FLICKER NOISE HAS THE LARGEST CONTRIBUTION TO THE TOTAL NOISE STRUCTURE OF THE SERIES. THE NOISE AMPLITUDES OF THE UP COMPONENT ARE LARGER THAN THOSE OF THE NORTH AND EAST COMPONENTS BY A FACTOR OF 2.5. IN ADDITION, IN ORDER TO OBTAIN CORRECT RATES, THE ANNUAL AND SEMI-ANNUAL SIGNALS ARE TO BE TAKEN INTO CONSIDERATION IN THE FUNCTIONAL MODEL. THIS COULD ALSO HOLD TO A LESSER EXTENT FOR THE gps DRACONITIC HARMONICS, ESPECIALLY FOR SHORT TIME SERIES.