Definities

 

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

 

De hier weergegeven definities zijn ontleend aan IMO Resolutie A.860(20).

A

Accuracy.
The degree of conformance between the estimated or measured parameter of a craft at a given time and its true parameter at that time. (Parameters in this context may be position coordinates, velocity, time, angle, etc.)

  • Absolute accuracy (Geodetic or Geographic accuracy). The accuracy of a position estimate with respect to the geographic or geodetic coordinates of the Earth.
  • Geodetic or Geographic accuracy. See Absolute accuracy.
  • Predictable accuracy.The accuracy of the estimated position solution with respect to the charted solution.
  • Relative accuracy. The accuracy with which a user can determine position relative to that of another user of the same navigation system at the same time.
  • Repeatable accuracy. The accuracy with which a user can return to a position whose coordinates have been measured at a previous time using uncorrelated measurements from the same navigation system.     

Ambiguity.
The condition obtained when one set of measurements derived from a navigation system defines more than one point, direction, line of position or surface of position. 

Augmentation.
Any technique of providing enhancement to the GNSS in order to provide improved navigation performance to the user.
  • Satellite-based augmentation system (SBAS). A system providing additional satellite signals in order to enhance the performance of the GNSS service.
  • Ground-based augmentation system (GBAS). A system providing additional signals from a ground-based station in order to enhance the performance of the GNSS service.     

Availability.
The percentage of time that an aid, or system of aids, is performing a required function under stated conditions. The non-availability can be caused by scheduled and/or unscheduled interruptions
  • Signal availability. The availability of a radio signal in a specified coverage area.
  • System availability. The availability of a system to a user, including signal availability and the performance of the user's receiver.     
C

Chart error.
Position errors in the chart caused by inaccuracies in surveying and by errors in the reference geodetic system. 

Circular error probable (CEP).
The radius of a circle, centered on the measured position, inside which the true position lies with 50% confidence. 

Confidence interval.
The numerical range within which an unknown is estimated to be with a given confidence. 

Confidence level.
The percentage of confidence that a given statement is correct, or the percentage of confidence that a stated interval (numerical range) includes an unknown. 

Confidence limits.
The extremes of a confidence interval. 

Continuity.
The probability that, assuming a fault free receiver, a user will be able to determine position with specified accuracy and is able to monitor the integrity of the determined position over the (short) time interval applicable for a particular operation within a limited part of the coverage area. 

Correction.
The numerical value of a correction is the best estimate that can be made of the difference between the true and the measured value of a parameter. The sign is such that a correction that is to be added to an observed reading is taken as positive. 

Coverage.
The coverage provided by a radionavigation system is that surface area or space volume in which the signals are adequate to permit the user to determine position to a specified level of performance. 

Cross-track error.
The component of the Vessel Technical Error perpendicular to the intended track. 

Craft autonomous integrity monitoring (CAIM).
This is a technique whereby various navigation sensor information available on the craft is autonomously processed to monitor the integrity of the navigation signals. (See also Receiver autonomous integrity monitoring.)

D

Differential system.
An augmentation system whereby radionavigation signals are monitored at a known position and the corrections so determined are transmitted to users in the coverage area. 

Dilution of precision.
The factor by which the accuracy of the GNSS position and time co-ordinates are degraded by geometrical considerations of the constellation of GNSS satellites used by the receiver.

  • Geometric dilution of precision (GDOP). The factor for the combined 3D-position and time accuracy.
  • Position dilution of precision (PDOP). The factor for the 3D-position accuracy.
  • Horizontal dilution of precision (HDOP). The factor for the horizontal position accuracy.
  • Vertical dilution of precision (VDOP). The factor for the vertical accuracy.
  • Time dilution of precision (TDOP). The factor for the time accuracy.     


Distance root mean square (dRMS).
The root mean square of the radial distances from the true position to the observed positions obtained from a number of trials. F

Failure.
The unintended termination of the ability of a system, or part of a system, to perform its required function. 

Failure rate.
The average number of failures of a system, or part of a system, per unit time. (See also mean time between failures.) 

Fix.
A position determined by processing information from a number of navigation observations. 

Fix rate.
The number of fixes per unit time. 

Fix interval (seconds).
The maximum time in seconds between fixes.

G

Global navigation satellite service.
The signal in space provided to the user by GNSS space and ground segments. 

GLONASS (Global Navigation Satellite System).
This is a space-based, radio positioning, navigation and time-transfer system operated by the Government of the Russian Federation. 

Global Navigation Satellite System (GNSS).
A world-wide position, time and velocity radio determination system comprising space, ground and user segments. 

Global Positioning System (GPS).
This is a space-based, radio positioning, navigation and time-transfer system operated by the United States Government. 

GNSS service.
The service relates to the properties of the signal in space provided by the space and ground segments of the GNSS. 

GNSS system.
The system relates to the properties of the GNSS service plus the receiver. 

Gross errors.
Gross errors, or "outliers", are errors other than random errors or systematic errors. They are often large and, by definition, unpredictable. They are typically caused by sudden changes in the prevailing physical circumstances, by system faults or operator errors.

I

Integrated navigation system.
A system in which the information from two or more navigation aids is combined in a symbiotic manner to provide an output that is superior to any one of the component aids. 

Integrity.
The ability to provide users with warnings within a specified time when the system should not be used for navigation. 

Integrity monitoring.
The process of the determination whether the system performance (or individual observations) allow use for navigation purposes. Overall GNSS system integrity is described by three parameters: the threshold value or alert limit, the time to alarm and the integrity risk. The output of integrity monitoring is, that individual (erroneous) observations or the overall GNSS system can not be used for navigation.

  • Internal integrity monitoring is performed aboard a craft.
  • External integrity monitoring is provided by external stations.     
Integrity risk.
The probability that a user will experience a position error larger than the threshold value without an alarm being raised within the specified time-to-alarm at any instant of time at any location in the coverage area. L

Latency.
The time lag between the navigation observations and the presented navigation solution.

M

Marginally detectable bias (MDB).
The minimum size of the gross error in an observation that may be detected with given probabilities of type 1 and type 2 errors. A type 1 error occurs when an observation without a gross error is wrongly rejected, and a type 2 error occurs when an observation with a gross error is wrongly accepted. 

Marginally detectable error (MDE).
The maximum position-offset caused by a MDB in one of the observations. 

Mean time between failures (MTBF).
The average time between two successive failures of a system or part of a system.

N

Navigation.
The process of planning, recording and controlling the movement of a craft from one place to another. 

Navigation system error (NSE).
The combined error of the GNSS position estimate and the chart error.
The maximum NSE can be described by:

NSEmax = Chart error + GNSS error + other navigation errors P

Pseudolite (pseudo satellite).
A ground-based augmentation station transmitting a GNSS-like signal providing additional navigation ranging for the user. 

Precision.
The accuracy of a measurement or a position with respect to random errors. 

PZ-90 geodetic system.
A consistent set of parameters used in GLONASS describing the size and shape of the Earth, positions of a network of points with respect to the centre of mass of the Earth, transformations from major geodetic datums and the potential of the Earth, developed in 1990.

R

Radio determination.
The determination of position, or the obtaining of information relating to position, by means of the propagation properties of radio waves. 

Radionavigation.
The use of radio signals to support navigation for the determination of position or direction, or for obstruction warning. 

Radiolocation.
Radio determination used for purposes other than radionavigation. 

Random error.
That error of which only the statistical properties can be predicted. 

Receiver autonomous integrity monitoring (RAIM).
A technique whereby the redundant information available at a GNSS receiver is autonomously processed to monitor the integrity of the navigation signals. (See also craft autonomous integrity monitoring.) 

Redundancy.
The existence of multiple equipment or means for accomplishing a given function in order to increase the reliability of the total system. 

Reliability (of an observation).
A measure of the effectiveness with which gross errors may be detected. This "internal" reliability is usually expressed in terms of the marginally detectable bias (MDB). 

Reliability (of a position fix).
A measure of the propagation of a non-detected gross error in an observation, to the position fix. This "external" reliability is usually expressed in terms of the marginally detectable error (MDE). 

Repeatability.
The accuracy of a positioning system, taking into account only the random errors. The repeatability is normally expressed in a 95% probability circle. 

Root mean square error (RMS).
RMS error refers to the variability of a measurement in one dimension. In this one dimensional case, the RMS error is also an estimate of the standard deviation of the errors.

S

Single point of failure.
That part of a navigation system that lacks redundancy, so that a failure in that part would result in a failure of the whole system. 

Systematic error.
An error which is non-random in the sense that it conforms to some kind of pattern. 

Service capacity.
The number of users a service can accommodate simultaneously.

T

Threshold value (or alert limit)
is the maximum allowable error in the measured position - during integrity monitoring - before an alarm is triggered. 

Time to alarm.
The time elapsed between the occurrence of a failure in the system and its presentation on the bridge. 

Total System Error (TSE).
The overall navigation performance can be described by the TSE. Assuming the contributions to TSE from NSE and VTE are random, the TSE can be described as:

TSE2 = NSE2 + VTE2
True position (2D).
The error-free latitude and longitude co-ordinates in a specified geodetic datum. 

True position (3D).
The error-free latitude, longitude and height co-ordinates in a specified geodetic datum. V

Vessel Technical Error (VTE).
This is the difference between the indicated craft position and the indicated command or desired position. It is a measure of the accuracy with which the craft is controlled.

W

World Geodetic System (WGS).
A consistent set of parameters describing the size and shape of the Earth, positions of a network of points with respect to the centre of mass of the Earth, transformations from major geodetic datums and the potential of the Earth.