Differential GNSS and Precise Point Positioning Lecture Vocabulary

Vocabulary and key terminology from Chapter 12 and 13 regarding Differential GNSS, Precise Point Positioning, and Inertial Navigation integration.

DGNSS

Differential GNSS; methods to improve the positioning or timing performance of GNSS by making use of measurements from one or more reference stations at known locations.

Precise Point Positioning (PPP)

A processing technique that uses accurate estimates of GNSS satellite orbits and clock errors from widespread networks to achieve high positional accuracy without nearby reference stations.

Baseline

The separation vector between a user and a reference station.

Short baseline

A baseline covering a distance of approximately $0$ to $20\,km$.

Medium baseline

A baseline covering a distance of approximately $20$ to $100\,km$.

Long baseline

A baseline spanning greater than $100\,km$.

Absolute differential positioning

The determination of a user's position with respect to an Earth-centered, Earth-fixed (ECEF) coordinate system.

Relative differential positioning

The determination of the user's position with respect to a coordinate system attached to the reference station(s).

LADGNSS

Local-area DGNSS; a system designed to function over a very small geographic area, typically with the user separated by less than $10$ to $200\,km$ from a single reference station.

WADGNSS

Wide-area DGNSS; a system that breaks out total pseudorange error into components (satellite ephemeris, clock, and ionosphere) to estimate variations over a large region.

Carrier-cycle integer ambiguity ($N$)

The unknown number of whole carrier cycles in the propagation path between a satellite and a receiver.

RTK

Real-time kinematic; the industry standard for centimeter-level positioning using carrier-phase measurements and real-time communication links.

Single difference (SD)

An interferometric variable created by differencing like measurements (such as carrier-cycle propagation path lengths) from two receivers for the same satellite.

Double difference (DD)

Formed by differencing two single-difference measurements to eliminate receiver and satellite clock-bias terms.

Phase wind-up

An effect caused by the relative rotation between a GNSS satellite and the user antenna that can change carrier-phase measurements by up to one cycle.

Solid Earth tides

Time-varying Earth surface movements dominated by diurnal and semidiurnal components in response to gravitational forces.

Ocean loading

Motion of the Earth's surface, particularly in coastal locations, caused by the weight of ocean tides.

Observation space representation (OSR)

Messages containing pseudorange corrections and raw measurements (pseudorange and carrier-phase) primarily needed for RTK.

State-space representation (SSR)

Messages providing data related to, for example, GNSS satellite clocks and ephemeris to the user.

GBAS

Ground-Based Augmentation System; augments GPS with a ground reference station at an airport to support precision approach, landing, and departure.

Inertial Navigation System (INS)

A secondary sensor system providing a reference trajectory immune to jamming and interference using gyroscopes and accelerometers.

Strapdown system

An inertial navigation system where instruments are fixed in the vehicle and the navigation frame is maintained mathematically.

Gimbaled system

An inertial navigation system where sensors are maintained in a preferred orientation on a physical platform isolated from the vehicle's attitude changes.

Gyroscope

An inertial sensor that outputs a signal proportional to angular movement ($\Delta\theta$) about its input axis.

Accelerometer

An inertial sensor that outputs a signal proportional to the change in velocity ($\Delta\nu$) sensed along its input axis.

Kalman filter

A mathematical estimator providing optimal estimates of the instantaneous state of a linear system perturbed by Gaussian white noise.