L

L Band

The group of radio frequencies extending from 390 MHz to 1550 MHz. The GPS carrier frequencies L1 (15735 MHz) and L2 (1227.6 MHz) are in the L-band

L1 signal / Frequency Band

The primary L-band signal transmitted by each GPS satellite at 1572.42 MHz. The L1 broadcast is modulated with the C/A and P-codes and with the navigation message

L2 signal / Frequency Band

The second L-band signal is centered at 1227.60 MHz and carries the P-code and navigation message

LAAS

Local Area Augmentation System. A system similar to WAAS, in that similar correction data are used. But in this case, the correction data are transmitted from a local source, typically at an airport or another location where accurate positioning is needed. These correction data are typically useful for only about a thirty to fifty kilometer radius around the transmitter

Latitude

An angular measurement (distance) of a point on the earth, north or south of the equator. The distance is measured in degrees, minutes, and seconds. Latitude is 0 degrees at the equator, +90 degrees at the North Pole, and -90 degrees at the South Pole (1 degree of latitude equaling 60 nautical miles and 1 minute of latitude being 1 nautical mile. Latitude is constant on a parallel). Lines (parallels) of latitude circle the earth horizontally and are parallel to one another

LDGPS

Local Differential GPS. Two or more GPS Receivers are used to create a local reference to each other

Line of Position (LOP)

Locus Of Points have a constant measurement (such as range, range difference). A fix is determined by crossing two lines of position

Local Area DGPS (LADGPS)

A form of DGPS in which the user's GPS receiver receives real-time pseudorange and, possibly, carrier- phase corrections from a reference receiver generally located within line of sight

Local-Area Augmentation System (LAAS)

A system similar to WAAS, in that similar correction data are used. But in this case, the correction data are transmitted from a local source, typically at an airport or another location where accurate positioning is needed. These correction data are typically useful for only about a thirty to fifty kilometer radius around the transmitter

Longitude

The angular measurement of a point on the earth's surface, east or west of the prime meridian. The prime meridian runs through Greenwich, England and is 0 degrees longitude. Since measurements are made East and West, the maximum longitude value is 180 degrees. Mathematically, longitudes are usually denoted as positive for easterly longitudes (e.g., +71 degrees = 71 E), and negative for westerly longitudes (e.g., -65 degrees = 65 W).

Loran

Long range navigation system that determines position by comparing the arrival times of radio signals with two or more master/secondary station pairs

M

Magnetic North

The direction to the Magnetic North Pole. It is what a magnetic compass indicates. It is different from True North, by the value of the Magnetic Variation

Magnetic Variation

The different between true North (pointing towards the Geographic Pole) and Magnetic North (pointing towards Magnetic Pole) where a compass points to. The magnetic variation of the earth changes at a rate of 50.27 seconds of arc per year

Map Datum

What reference map is used in determining the Fixes

Map projection

The systematic arrangement of the earth's spherical or geographic coordinate system onto a plane; the process of transforming a globe into a flat map with the least amount of distortion; a transformation process

Mask angle

Cut off angle The point above the observer's horizon below which satellite signals are no longer tracked and/or processed. 10° to 25° is typical

MCX

Antenna connector used on some of the newer GPS units

Megahertz (MHz)

One million cycles per second. Used to describe a radio frequency

Meridian

An imaginary line that circles the earth, passing through the geographic poles and any given point on the earth's surface. All points on a given meridian have the same longitude

MGRS

Military Grid Reference System. The MGRS is an alphanumeric version of a numerical UTM (Universal Transverse Mercator) or UPS (Universal Polar Stereographic) grid coordinate

Microstrip Antenna

A type of antenna commonly used with GPS receivers. It is usually constructed of one or more (typically rectangular) elements that are photoetched on one side of double-coated, printed-circuit board

Military Grid Reference System (MRGS)

A alphanumeric version of a numerical UTM (Universal Transverse Mercator) or UPS (Universal Polar Stereographic) grid coordinate.

MOB

Man Over Board. A button to take an immediate fix, so you can find a lost person

Modulation

A method of encoding a message signal on top of a carrier, which can be decoded at a later time

MOPS

Minimum Operational Performance Standards

MRGS

The Military Grid Reference System is an alphanumeric version of a numerical UTM (Universal Transverse Mercator) or UPS (Universal Polar Stereographic) grid coordinate.

MSAS

Multi-functional Satellite Augmentation System, operation in Asia

Multi-channel receiver

A GPS receiver that can simultaneously track more than one satellite signal

Multipath

Interference caused by reflected GPS signals arriving at the receiver, typically as a result of nearby structures or other reflective surfaces

Multipath error

Errors caused by the interference of a signal that has reached the receiver antenna by two or more different paths. Usually caused by one path being bounced or reflected

Multiplexing

The technique used in some GPS receivers of rapidly sequencing the signals of two or more satellites through a tracking channel. This ensures navigation messages from the satellites tracked by the channel are essentially acquired simultaneously

Multiplexing channel

A channel of a GPS receiver that can be sequenced through a number of satellite signals