N

NAD 83

Horizontal coordinate system for U.S., Canada and Mexico. Originally published in 1986 it is based upon the GRS 80 ellipsoid with its origin at the center of mass defined by BIH at epoch 1984.0. Geodetic surveyors must be particularly cognizant of epoch dates attached to the NAD 83 an acronym. These refer to the mean date of the observations used in the regional adjustment

NAD27

North American Datum 1927. It is broken down into different areas, from Central America to Greenland

NAGU

Notice Advisory to GLONASS Users. A periodic bulletin alerting GLONASS users to changes in system performance.

NANU

Notice Advisory to NAVSTAR Users.  A periodic bulletin alerting GPS users to changes in system performance

Narrow Correlator

A correlator in a code-tracking loop in which the spacing between the early and late versions of the receiver-generated reference code is less than one chip. The use of narrow correlators results in pseudorange observations with lower noise

Narrow Lane

The GPS observable obtained by summing the carrier-phase observations simultaneously measured, in cycles, on the L1 and L2 frequencies. The effective wavelength of the narrow-lane observable is 10.7 centimeters. The narrow-lane observable can help resolve carrier-phase ambiguities

Nautical Mile

A distance of 18519999 meters which is one minute of arc of a great circle of the Earth (1.15 times longer than a statute mile, or 6076.1 feet)

NAVD 88

Vertical (elevation) reference system for U.S., Canada and Mexico. Published in 1991 the orthometric heights are derived from an adjustment of leveling data constrained at a single point on the St. Lawrence Seaway

Navigation Message

A 37500-bit data message included in the GPS signal. The message, sent at a rate of 50 bits per second, includes the satellite ephemeris, clock data, almanac, and other information about the satellites and their signals

NAVSTAR

NAVigation Satellite Timing and Ranging. The name given to GPS satellites

NDGPS

Nationwide Differential GPS, The NDGPS plan calls for the conversion of a number of U.S. Air Force Ground Wave Emergency Network (GWEN) sites to broadcast DGPS signal. The range is 250 miles

NEMA

National Electrical Manufacturers Association

NEMA 0183

A communication protocol used by GPS units and other types of navigation and marine electronics

NGVD 29

Mean sea level reference system for U.S. prior to NAVD 88. Constrained to 26 tide stations in U.S. and Canada, the datum is distorted to fit sea surface topography

NIMA

National Imaging and Mapping Agency

NMEA

National Maritime Electronics Association. The association sets standards for interfacing nautical electronic devices, including Global Positioning System receivers

Noise

An interfering signal that tends to mask the desired signal at the receiver output and which can be caused by space and atmospheric phenomena, can be human made, or can be caused by receiver circuitry

Notice Advisory to GLONASS Users (NAGU)

A periodic bulletin alerting GLONASS users to changes in system performance

Notice Advisory to NAVSTAR Users (NANU)

A periodic bulletin alerting GPS users to changes in system performance

NSDI

National Spatial Data Infrastructure

NSTB

FAA's National Satellite Test Bed

NTSB

National Transportation Safety Board

O

On-the-Fly (OTF)

The term used to identify a technique that resolves differential carrier-phase integer ambiguities without requiring a GPS receiver to be stationary at any time

Ordnance Survey Maps (OSM)

Britain's National Mapping Agency

Orthometric Height

The height of a point above the geoid

Oscillator

A device that generates a signal of a given frequency

OSM

Ordnance Survey Maps. Britain's National Mapping Agency

OziExplorer

Scanned map software for use with GPS.