SOURCES OF ERROR IN GPS MEASUREMENTS
GPS satellites have errors due to source ephemeris errors and those of watches from satellites. It is obvious that affects positioning accuracy ephemeris errors. Some authors estimate very optimistic, positioning error of 1.5 m, due to imprecision ephemeris. Others say that the value is only mentioned imprecision effect radial position of the satellite, the total error is two or three times higher. The estimates are obtained navigation solution with ephemeris broadcast navigation message of GPS signals and received by the user.
In GPS measurements allegedly directly from the satellite signal reaches the receiver. But this is not always true, with the direct signal reaching the receiver and reflected signals due to contact with the ground or other objects before reaching the antenna. If the difference of the road traveled by the two signals (direct and reflected) is considerably high (greater than 10 m) then we can make a difference between the signal goes directly to the receiver and the signal was reflected. If the path difference is small, there is an uncertainty of determining the direct and implicitly signal timing at which it was perceived.
Most RTK GPS systems, using low frequency UHF radio modems. Radio communication is the part of RTK system that most users experiencing difficulties. Worth considering the following factors influence when radio link performance optimization test: power radio transmitter. Generally speaking, more power means better performance. However, most countries restrict legal transmit power to 0,5-2W. Transmitter antenna height. Radio communications may be affected by line of sight. The higher the antenna is positioned, the more unlikely to be problems with line of sight. It will also increase the range of radio communications. The same applies to the receiving antenna. Other influencing factors affecting performance include the length of the cable to radio antenna (longer cables mean higher losses) and the type of radio antenna used.
The abbreviation comes from the kinematic RTK in real time. It is a method of measuring kinematic OTF which takes place in real time. Fixed Station has a radio link attached and retransmits data it receives from the satellites. The handset has a radio link and receives transmitted by fixed station.
The handset otherwise receives data directly from satellites through its own Phone Tracker antenna. These two sets of data can be processed along the rover to resolve ambiguity and therefore will get a high accuracy relative to the fixed receiver. Once the fix was installed receiver and transmit data via radio link, the rover can be activated. When aims satellites and the data from the fixed initialization process can begin. This is similar to the initialization performed when OTF kinematic measurements, the main difference being that it is brought to an end in real time.
This is a variant of the method and removes requirements cinematic initialization and initialization following notice when the number of satellites drops below 4. OTF kinematic method is a processing method that is applied during post-processing measurements. Earlier measurements, the operator can simply move the receiver and record data. If he goes under the crown of a tree and lose the satellites, upon entry into satellite coverage, the system will reboot automatically.
An important aspect to be pursued is that during measurement to avoid approaching objects that could block the satellite signal to the rover. If at any time during measurement mobile observed less than 4 satellites, the measurement must be stopped, the receiver must be moved to a position in which four or more satellites are observed and must be redone initialization before further measurements.