MINIMUM DETECTABLE SIGNAL—A received
signal whose power is just above the noise level of
the receiver.
MSL—Mean sea level. a suffix used after altitude
measurements.
N
NADIR—The position directly under a satellite on the
earth’s surface at a specific point in time. Also,
subpoint.
NESDIS—National Environmental Satellite, Data,
and Information Service, adivision of NOAA.
NEXRAD—Acronym for NEXt generation RADar
(WSR-88D Doppler radar).
NIPRNET—Unclassified Internet Protocol Routing
Network.
NOAA—National Oceanic and Atmospheric
Administration. NOAA is an agency of the U.S.
Department of Commerce.
NODAL INCREMENT—The longitude, in degrees,
between successive northbound equatorial
crossings of a polar-orbiting satellite.
NODAL PERIOD—The period, in minutes. between
successive northbound equatorial crossings of a
polar-orbiting satellite.
NODDS—Navy Oceanographic Data Distribution
System.
NOISE—Any unwanted, usually random, fluctuation
of a signal.
NON-ASSOCIATED PRINCIPAL USER—A
principal user with access to a WSR-88D system
through means of dial-in telecommunications.
NWRN—National Weather Radar Network.
NWS—National Weather Service, a division of
NOAA.
NYQUIST VELOCITY—The maximum unambig-
uous velocity that can be measured by a Doppler
radar.
O
OKTAS—Eighths of the sky.
ORBIT—The path that a satellite follows in its motion
through space, relative to the earth.
OUTFLOW BOUNDARY—The leading edge of
horizontal airflow resulting from cooler, denser air
sinking and spreading out at the surface. Often
caused by the downdraft of thunderstorms.
P
PERIGEE—The lowest point (shortest distance from
the surface) in a satellite orbit.
PERIOD—A general term for the time required for
one orbit around the earth.
PHASE—A particular angular stage or point of
advancement in a cycle; the fractional part of the
angular period, through which the wave has
advanced, measured from the phase reference.
PIXEL—The individual component of an image scan
line defined by a single video sample in a digital
image system. The greater the number of pixels in
a line, the greater the display’s resolution.
POES—Polar Orbiting Environmental Satellite.
POLAR ORBITING—Satellites with high orbital
angles, crossing over the polar regions of the earth.
PRINCIPAL USER—Principal users of the WSR-
88D are the National Weather Service (NWS), the
Air Force Weather Agency (AFWA), the Naval
Meteorology and Oceanography Command,
Marine Corps Weather Service Units, and the
Federal Aviation Administration.
PROPAGATION—Transmission ofelectromagnetic
energy as waves through or along a medium.
PULSE—A single short duration transmission of
electromagnetic energy.
PULSE DURATION—Time occupied by a burst of
transmitted radio energy. This may also be
expressed in units of range (pulse length).
PULSE REPETITION FREQUENCY (PRF)—The
number of radar pulses transmitted per second.
PULSE REPETITION TIME (PRT)—The time
interval from the beginning of one pulse to the
beginning of the next succeeding pulse.
PULSED RADAR—A type of radar designed to
facilitate range measurement in which transmitted
energy is emitted in periodic, brieftransmissions.
AI-4
