A B C D E F G H I J K L M N O P Q R S T U V W X Y Z C/A code The coarse/acquisition or clear/acquisition code modulated onto the GPS L1 signal. This code is a sequence of 1023 pseudorandom binary biphase modulations on the GPS carrier at a chipping rate of 1.023 MHz, thus having a code repetition period of 1 millisecond. The code was selected to provide good acquisition properties. Also known as the "civilian code" or S-code. Cadastral Survey Survey performed to establish legal and political boundaries, typically for land ownership and taxation purposes. Carrier A radio wave suppling the energy upon which information may be carried. The information (Data) is transported by modifying the carrier. That is by changing its frequency, amplitude, phase or buy interrupting it. Carrier aided tracking A signal processing strategy that uses the GPS carrier signal to achieve an exact lock onto the pseudorandom code. More accurate than standard approach. Carrier beat phase The phase of the signal which remains when the incoming Doppler-shifted satellite carrier signal is beat (the difference frequency signal is generated) with the nominally-constant reference frequency generated by the receiver. Carrier frequency The frequency of the unmodulated fundamental output of a radio transmitter. The GPS L1 carrier frequency is 1575.42 Mhz. Carrier phase GPS GPS measurements based on the L1 or L2 carrier signal. CAT CATegory CDMA See code division multiple access Celestial Equator The great circle that is the projection of the Earth's geographical equator of rotation onto the celestial sphere. Its poles are the North and South Celestial Poles. Celestial meridian The vertical circle that passes through the elevated celestial pole. It also passes through the other celestial pole, the astronomical zenith, and the nadir. CGSIC Civil GPS Service Interface Committee Channel A channel of a GPS receiver consists of the radio frequency, circuitry, and software necessary to tune the signal from a signal GPS satellite. Chip In the GPS world, a chip is the length of time to transmit either a "0" or a "1" in a binary pulse code. Chip rate Number of chips per second (e.g. C/A code = 1.023 Mhz). Circular error probable (CEP) In a circular normal distribution, the radius of the circle containing 50 percent of the individual measurements being made, or the radius of the circle within which there is a 50 percent probability of being located. Civilian code See C/A code. Clock bias The difference between the clock's indicated time and the true universal time. Clock offset (Clock Error) Constant difference (error) in the time given by two clocks. Code division multiple access (CDMA) A method of frequency reuse whereby many radios use the same frequency but each one has a unique code. GPS uses CDMA techniques with Gold's codes for their unique cross-correlation properties. Code phase GPS GPS measurements based on the pseudo random code (C/A or P) as opposed to the carrier of that code. Cold Start The process of powering up a new GPS receiver for the first time and having it search out and lock onto the satellites by itself, without the benefit of initialization data. This procedure is slower and may require up to 15 minutes for initial satellite acquisition only. Computer-aided dispatch An automated system for processing dispatch business and automating many of the tasks typically performed by a dispatcher. Abbreviated CAD (not to be confused with computer-aided design which is also known as CAD) is application software with numerous features and functions. A basic CAD system provides the integrated capability to process calls for service, fleet management and geographical referencing. Constellation Refers to either the specific set of satellites used in calculating positions or all the satellites visible to a GPS receiver at one time. Continuously Operating Reference Stations (CORS) COERS is an outgrowth of real-time Differential GPS stations operated in support of marine and air Navigation. Currently CORS sites are accurate to within 3 Centimeters horizontally and 5 centimeters vertically relative to each other , but NGS expects to have this down to 1 centimeter horizontally and 2 centimeters vertically with in six months. Control point Also called a control station. A monumented point to which coordinates have been, or are being assigned by the use of surveying observations. The National Geodetic Survey maintains a nation-wide set of control points. Control segment A world-wide network of GPS monitor and control stations that ensure the accuracy of satellite positions and their clocks. Conventional international origin (CIO) Average position of Earth's rotation axis during the years 1900 to 1905. Correlation channel A GPS receiver channel that uses a delay lock loop to maintain an alignment (correlation peak) between the copy of the GPS code generated by the receiver and the received GPS code. Course Over Ground (COG) The current direction (in degrees) that you are actually traveling. (Again selectable in degrees magnetic or true north). Cross Correlation The signal derived from correlating the L1 frequency with the L2 frequency. This is a method for countering the encryption of the Pcode to the secret Y code as it allows the reconstruction of the carrier wave on L2. The resultant carrier has a much reduced signal quality when compared to the unencrypted signal. Cross Track Error (XTE) Digital reading on GPS steering screens that indicates precisely how far off you are, to the right or left of the center of the course. Cycle Slip A discontinuity in the carrier phase measurement resulting from a temporary loss of lock in the carrier tracking loop of a GPS receiver. It indicates that a receiver has momentarily lost the signal from a satellite. A B C D E F G H I J K L M N O P Q R S T U V W X Y Z