Different Antennas: Helices 5. Multipath The direct computation of the antenna effects on the distance measurements with respect to azimuth an elevation was proposed Multipath: a satellite emitted signal arrives at the receiver via more than one path There is no general model of the multipath effect because of Causes: he arbitrarily different geometric situations 1. reflecting surfaces near the receiver Estimation methods: 2. reflections at the satellite during signal transmission The influence of the multipath can be estimated Result: oposphere, clock errors, and relativistic effects Phase differences differences of the path Improvement Methods: Er rror 1. Selecting an antenna that takes advantage of the signal 10-20 m for code pseudoranges 2. digital filtering, wideband antennas, radio frequency about 100 m in the vicinity of buildings absorbent antenna ground planes, and choke ring on carrier phases for relative positionin antennas baselines, generally, not be greater tha satellite geometry and a reasonably long 二c 3. The absorbent antenna ground plane reduces the interference of satellite signals with low or even negative nterval) elevation angles which occur in case of multipath 4. The height of th ver, or ground 5. With static surveys, observation times long, 6. With intermittent observation time long, metal trucks continually pass by the antenna.5 Different Antennas: • Conical spiral antennas, • Microstrip antennas, • Dipole antennas (crossed pair of horizontal, half￾wavelength dipole) • Helices. The direct computation of the antenna effects on the distance measurements with respect to azimuth and elevation was proposed. 5. Multipath Multipath: a satellite emitted signal arrives at the receiver via more than one path. Causes: 1. reflecting surfaces near the receiver, 2. reflections at the satellite during signal transmission. • Phase offsets due to Multipath • Phase differences are proportional to the differences of the path lengths. Result: There is no general model of the multipath effect because of the arbitrarily different geometric situations. The influence of the multipath can be estimated by using a combination of L1 and L2 code and carrier phase measurements. The principle is based on the fact that the troposphere, clock errors, and relativistic effects influence code and carrier phases by the same amount. Modeling: Estimation Methods: Error: • 10-20 m for code pseudoranges • about 100 m in the vicinity of buildings • on carrier phases for relative positioning with short baselines, generally, not be greater than 1 cm (good satellite geometry and a reasonably long observation interval), 1. Selecting an antenna that takes advantage of the signal polarization. 2. digital filtering, wideband antennas, radio frequency absorbent antenna ground planes, and choke ring antennas. 3. The absorbent antenna ground plane reduces the interference of satellite signals with low or even negative elevation angles which occur in case of multipath 4. The height of the receiver, or ground 5. With static surveys, observation times long, 6. With intermittent observation time long, 7. Avoid to set up in the center of a highway and large metal trucks continually pass by the antenna. Improvement Methods: