Domestic accustomed to GNSS RTK receiver called into this is true, because of the popularity of RTK technology, so that everyone on the receiver's role is "limited" in the RTK, in the absence of RTK before the receiver is the receiver.
Currently, GNSSj receiver about 99% of the time used to measure RTK mode, only 1% of the time measurement made available as static control network. Therefore, most people are used to GNSS RTK receiver shouting into a.
But removing the GNSS receiver, RTK you know what that means?
Positioning
before said RTK, we must first understand the meaning of the word - satellite positioning, is a value on something accurate positioning using satellite technology.
The use of satellite positioning technology, developed from earlier Meridian satellite systems now well known global positioning system and regional positioning system, developed very rapidly.
Then you know how to know your location via satellite do?
With the US GPS system, for example, we look at the basic principles of GPS satellite positioning: measuring the position of the satellite known to the distance between the user receiver and integrated data from multiple satellites can know the specific location of the receiver. And because the need to calculate three-dimensional position and deviation, it requires at least four satellites. (If you use when measuring only found to three satellites, it is absolutely impossible fixed.)
There is the most important thing is to measure the distance between the satellite and the user receiver, how to measure it? Start with a basic mathematical principle: distance = speed X time.
Satellite positioning technology, too, is the short answer is that the satellite signal to the user in space, after a period N, the user received a satellite signal on Earth. N multiplied by the speed of light to obtain the time distance between the satellite and the user.
Position of the satellite in the satellite ephemeris may be obtained in a known position of the satellite the distance to the satellite and the user, so that user's location information is obtained.
Due to the interference of the atmosphere ionosphere, this distance is not the true distance between the user and satellites, but pseudorange. We call this measuring method is called pseudo-range measurements. Because of the positioning accuracy, it has developed a carrier phase measurements.
For the interference of satellite positioning, of course, not just the atmosphere ionosphere interference, further comprising a clock error, ephemeris errors, etc., you have to want to learn more about, the previous reference Xiao Bian article "look GPS positioning error sources and weaken method" .
Well, on the positioning stop here, then on and Xiaobian know about RTK technology.
First of all, we have to know the basic concepts of RTK, RTK English Real - time kinematic abbreviation, Chinese meaning is real-time dynamic. RTK satellite navigation is a technique for increasing the accuracy of GNSS-based positioning (GPS / BeiDou / Galileo / Glonass) obtained data.
So, what concept RTK is it? It is a carrier phase measurement using GPS technology for real-time dynamic relative positioning, it is possible to provide three-dimensional positioning results in the station designated coordinate system in real time. When using an RTK survey ...
Etc., the carrier What does it mean? Some people may not know what it meant, small series for everyone to simply explain.
2 carrier phase
carrier that, according to its name can learn the meaning of the carrier means is a carrier wave of a radio wave is meant, of course, here to the satellite carrier signals, together to carry the modulated signal is a high frequency oscillation wave, called a carrier.
The GPS system, for example, the GPS satellite signals transmitted by the three-part carriers, ranging codes and navigation message composition (Do not ask why this small series of three components). Ranging codes and carriers used for distance measurement, navigation message includes satellite ephemeris, satellite clock correction parameters
built in the beginning of GPS, positioning is carried out by a pseudo-range measurements, because of the low accuracy (C / A code the ranging accuracy can only reach 2.93m), then people in the mid-1990s to develop GPS-based measurements (or more generally, based GNSS measurements) in real-time centimeter-level positioning accuracy, which is now RTK ( "real-time dynamic" ) positioning.
Wonder why pseudo-range measurements lower than the carrier phase accuracy of it?
Because the code width and wavelength ranging code pseudorange measurements are measured as the signal, while using code correlation method, the measurement accuracy is one percent of the width of the symbols, since the ranging code symbol large width (fine amble width 30m, C / A code having a code width 300m), thus resulting in measurement accuracy.
Width calculation code: code width ÷ the code frequency = speed of light, the speed of light, the code frequency C / A code is 1.023 MHz (), the fine code is the code frequency 10.23Mhz ().
And the carrier will have a much shorter wavelength (19.0cm / 24.4cm / 25.5cm), as the carrier phase measurement ranging signal, will be able to achieve high accuracy.
Having said that, the small series suddenly thought of one thing, before the carrier as a carrier (slave labor) carrying satellite signals, and ranging code is also included in the satellite signal, the carrier is to explain ranging code when the vehicle suddenly found as a means of transport carriers even higher accuracy than a ranging code, ups and downs.
However, when using the carrier is not all good, there are also disadvantages. Problems such as cycle slip and ambiguity of the whole week there will be, Xiao Bian explain two words for everyone.
First, the cycle slip, because the entire circumference of the satellite signal due unlock resulting jump or interrupt count, resulting in inaccurate observations.
Ambiguity is because the carrier is a cosine wave without any distinguishing mark, the phase detector within the receiver portion of only the measurement of less than a week, the number generated for the entire circumference of uncertainty. The question you need to look at the manufacturers test measurement software computing power for the entire week of the technology.
Then we look at the carrier phase measurement principle is, look at the formula
is a satellite to the Earth's distance, also known as Wei from the ground, for the carrier wavelength, phase difference, the phase difference here contains a fractional part less than a week, also contains a number of bands in the entire circumference.
Therefore, the actual carrier phase measurement unit of length is the wavelength, in order to measure the distance between the carrier satellite to the receiver as a "ruler."
3RTK
carrier finished, then he said RTK, RTK is a carrier phase measurement using GPS technology in real-time dynamic relative positioning, keyword: real-time, dynamic and relative positioning.
Previous static, rapid static and dynamic measurements need to be post-solver to get centimeter accuracy, and be able to get real-time RTK centimeter level accuracy measurements in the field, greatly improved work efficiency.
Working principle is the RTK base station through the data link to be transmitted to the rover together with their observations and the station coordinates information. Rover only receive data through the data link from the base station, but also collect GPS observations, and observations constitute a differential value in the real-time processing system, centimeter-level positioning and gives results.
Therefore, measuring RTK GPS receiver requires at least 2 (as one or more base station as a mobile station), a data communication link (radio, etc.) and measurement software.
The above said small series are conventional RTK, RTK has a conventional flaw, the error is GPS reference station will increase with the distance of the mobile station and gradually lose linearity at longer distances (Single Frequency> 10km, dual> 30km), after the difference processing user data still contains a great measurement error, resulting in ambiguity and the positioning accuracy can not be reduced solving the carrier phase.
So in the mid-1990s, it has been proposed Network RTK technology. A plurality of reference stations by GPS network to estimate a GPS error model area and the user area provides correction data for the network coverage, a virtual reference station data, and provide users with a network of reference positions close to their distance grid correction data, the network RTK technique is also known as virtual reference station (virtual reference).
In recent years with the development of technology, RTK technology has been developed from the traditional 1 + 1 or 1 + 2 to the wide area differential system WADGPS, some cities established CORS system, some companies have established their own CORS system, such as Spirited Away CORS, which greatly improves the measurement range RTK, RTK solve the traditional distance limitations.
Summary
RTK is a carrier phase measurement using GPS technology in real-time dynamic relative positioning, the carrier although high accuracy, and problems circumferential ambiguity jump but also appear.
RTK development from the traditional RTK to RTK network to the current CORS, precision measurement more convenient and more accurate.
Key RTK technique is that the data processing and data transmission technology, requires base station receiver RTK positioning when the real-time observation data (pseudorange observations phase observations), and the known data to the rover receiver, comparing the amount of data Big.
RTK data is also transmitted by the radio transmission to today's GSM and GPRS network transmission, greatly improving the efficiency and range of data transmission.
