Real time Kinematic GPS
It uses measurements of the phase of the signal's carrier wave in addition to the information content of the signal and relies on a single reference station or interpolated virtual station to provide real-time corrections, providing up to centimetre-level accuracy.
The way to tell this is also RTK data is by the carrier's almost "musical-beat" like sounding pulse, representing a random binary sequence. With reference to GPS in particular, the system is commonly referred to as carrier-phase enhancement, or CPGPS. It has applications in land survey, hydrographic survey, and in unmanned aerial vehicle navigation.
The distance between a satellite navigation receiver and a satellite can be calculated from the time it takes for a signal to travel from the satellite to the receiver. To calculate the delay, the receiver must align a pseudorandom binary sequence, contained in the signal to an internally generated pseudorandom binary sequence Since the satellite signal takes time to reach the receiver, the satellite's sequence is delayed in relation to the receiver's sequence. By increasingly delaying the receiver's sequence, the two sequences are eventually aligned. (hence the result of the music beat-sequence).
The signal is primarly used on farms to measure distance and other related info as well.
^^ A bit of a slower one, half the rate of this page's audio sample.