C

C Code

The less accurate Civilian GPS Signal. See Selective Availability

C/A code

The standard (Course/Acquisition) GPS code. A sequence of 1023 pseudo-random, binary, biphase modulations on the GPS carrier at a chip rate of 1.023 MHz. Also known as the "civilian code" or S-code

Call Sign

Each amateur radio station is assigned a call sign by the government of that country which allows the operator to transmit in the amateur radio bands

Carrier

A radio wave having at least one characteristic (e.g. frequency, amplitude, phase) that can be varied from a known reference value by modulation

Carrier frequency

The frequency of the unmodulated fundamental output of a radio transmitter

Carrier Phase

GPS measurements based on the L1 or L2 carrier signal

Carrier-Aided Tracking

A technique to improve accuracy by using the GPS carrier signal to get a more exact lock on the pseudorandom code

Carrier-to-Noise Power Density (C/N0)

The ratio of the power level of a signal carrier to the noise power in a 1-Hz bandwidth. This is a key parameter in the analysis of GPS receiver performance. Nominal GPS receiver C/N0 values often are in the 40 to 50-dB-Hz range

Carrier-Tracking Loop

A module in a GPS receiver that demodulates, or extracts, the satellite message by aligning the phase of the receiver's local oscillator signal with the phase of the frequency-shifted, received carrier. Once the local oscillator signal is locked to the carrier, its phase can be measured to provide the carrier-phase observation

Channel

A channel of a GPS receiver consists of the circuitry necessary to receive the signal from a single GPS satellite

Chip

Binary elements or digits that, unlike bits, convey no information. A PRN code consists of a sequence of chips

CIB

Controlled image base

Circular Error Probable (CEP)

A statistical measure of the horizontal precision. The CEP value is defined as a circle of a specified radii that encloses 50% of the data points

CITS

Close Air Support Integrated Targeting System is a program developed by Northport Systems Inc. for integrating the Global Positioning System with laser target locators

Clarke 1866

The reference ellipsoid for the NAD27 coordinate system

Clock Aiding

An accuracy enhancement technique in which an additional atomic clock (rubidium) provides accurate time to the receiver for calculating satellite clock frequency, phase bias, and clock drift

Clock Bias

The difference between a clock's indicated time and true universal time

CMG

Course Made Good. How you are progressing towards your next waypoint

Coarse Acquisition (C/A)-Code

A family of PRN codes transmitted by GPS satellites. Each satellite is assigned one of 32 unique codes in the family. Each code consists of 1,023 chips and is sent at a rate of 1.023 megabits per second. The code sequence repeats every millisecond. The C/A-codes are Gold codes -- PRN codes that are distinguished by a very low cross correlation between any two codes (that is, they are nearly orthogonal). C/A-codes currently are transmitted only on the L1 frequency

Code Division Multile Access (CDMA)

A technique of multiplexing, also called spread spectrum, in which analog signals are converted into digital form for transmission. For each communication channel, the signals are encoded in a sequence known to the transmitter and the receiver for that channel

Code phase GPS

GPS measurements based on the pseudo random code (C/A or P) as opposed to the carrier of that code

Code-Tracking Loop

A module in a GPS receiver used to align a PRN code sequence present in a signal coming from a satellite with an identical PRN code sequence generated within the receiver. Alignment is achieved by appropriately shifting the receiver-generated code chips in time so that a particular chip in the sequence is generated at the same instant its twin arrives

COG

Course Over Ground, Your current direction of travel relative to a ground position (same as Track)

Cold Start

The ability of a GPS receiver to start providing position updates without the assistance of any almanac information stored in its memory

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

Continuous Kinematic Surveying

Successive baseline solutions generated at every epoch of an unbroken observation set. Typically used to track a vehicle or platform in motion

Contour line

A line on a map that connects points of equal elevation

Control point

Also called a control station. The National Geodetic Survey maintains a nation-wide set of control points. A world-wide network of GPS monitoring and control stations that ensure the accuracy of satellite positions and their clocks

Control Segment

That portion of the Global Positioning System that consists of a master control station, monitoring stations, and ground antennas, which monitor and update satellite signals and upload correction data to the satellites

CONUS

Continental United States. An Abbreviation used in a class of Datums

Coordinated Universal Time (UTC)

See UTC

Correlation

The extent to which one observation or computed value is influenced by the change in an other, or that both are influenced by a third. The correlation coefficient is the proportion of the total variation in the dependent variable (y) which can be attributed to the relationship with the independent variable (x)

CORS

Continuously Operating Reference Station Fixed GPS receiver site in continuous operation

Course Made Good (CMG)

The bearing from the starting point to the present position

Course Over Ground (COG)

Your current direction of travel relative to a ground position

Cross-Track Error (XTE)

The difference between a vessel's actual position and its desired position on a given heading. This is usually measured as a range error in nautical miles but may also be expressed graphically using symbols

CTS

Course To Steer

Cycle Slip

A discontinuity in GPS carrier-phase observations, usually of an integer number of cycles, caused by temporary signal loss. If a GPS receiver loses a signal temporarily, due to obstructions for example, when the signal is reacquired there may be a jump in the integer part of the carrier-phase measurement due to the receiver incorrectly predicting the elapsed number of cycles between signal loss and reacquisition