Page 156 - Radar Technology Encyclopedia

146 display, sector distribution, binomial

with polar or rectangular sweep. These are actually modifica- radar, relative to a fixed background; accomplished by insert-
tions of the plan-position indicator (PPI) or the rectangular- ing compensation for the motion of the vehicle carrying the
coordinate display. For example, in a PPI the center of rota- radar.” SAL
tion of the sweep can be offset from the center of the screen to Ref.: IEEE (1993), p. 1417.
the side opposite the enlarged sector and the scale expanded
A two-dimensional (2D) display is one that presents two
in range and angle by a factor typically two to four (an off-
coordinates of a radar target. Usually CRT displays are used
center PPI). IAM
with a bright blip from the target in the rectangular or polar
Ref.: Ridenour (1947), p. 168; Rakov (1966), vol. 2, p. 140.
(plan-position indicator) coordinate system. Thanks to the use
A special display is one used in a specific type of radar or of a screen with persistence, the bright blips carrying the
under specific conditions of operation. Examples are bright information concerning the air or ground situation are main-
displays operating in high-ambient-light environments, dis- tained for the scanning period. CRTs with electrostatic deflec-
plays for sidelooking radars that must present high-resolution tion and magnetic deflection are used to ensure a better
ground maps, those of terrain-avoidance radars that must focusing of the beam.
carry the information on aircraft clearance height, and large- Two or more 2D indicators that have a common indexed
screen displays that present the same information to several coordinate for the correlation of the displays are used for the
people (e.g., in command and control centers). These last take full display of the spatial disposition of the targets (e.g., azi-
the form of projection displays (dynamic slides, photochro- muth-range and altitude-range displays). IAM
mic-film projection, etc., or liquid-crystal displays). IAM Ref.: Barton (1964), p. 7; Vasin (1977), p. 181.
Ref.: Skolnik (1970), p. 6.24.
A volume display presents a volume image. It is based on the
A synthetic-video display is one in which target information stereo effect, using a pair of conventional radar displays or by
is presented with standard symbols and accompanying alpha- using optometrical means. In the latter case tipping or rotating
numerics. The computer is used to generate the graphics and screens or mirrors are used on which by optical means an
control the CRT display, so it offers flexibility in choice of image is projected that is usually the bright blip of a target.
different modes of operation and provides the possibility of The mirror is connected by means of a synchronized tracking
implementing many functions necessary, for example, in air- system with the radar antenna and repeats the movement of
traffic-control or air-defence systems (e.g., blanking the areas the beam. Two other coordinates lie in the plane of the screen.
with excessive interference, superimposing simulated targets IAM
to provide the training of radar operators,). Typically this type Ref.: Poole (1966), p. 276; Druzhinin (1967), p. 425.
of display will be digital. SAL
DISTANCE (see RANGE).
Ref.: Skolnik (1980), p. 359.
A television [-type] display is a radar display in which the DISTRIBUTION. The term distribution is used in radar in
brightness of the image is increased as a result of multiple two ways: (1) to describe the relative frequency of occurrence
regeneration of the area of the radar image recorded within of random events (probability density and probability distri-
the space of one scanning cycle and the display of the regen- bution functions) and (2) as a synonym for taper, illumina-
erative images with a great repetition frequency. The opera- tion, or weighting of an antenna aperture. The probability
tion of the display is based on the conversion of the radar distribution functions ware described below. The weighting
image into a television image, which is usually accomplished of an aperture, or equivalent time or frequency function in
using CRTs with storage capability. The brightness of this signal processing, is described under the WEIGHTING
2
type of television image is 170 to 350 candles/m . However, entry. SAL
at the same time, the resolution and number of gradations of
aperture distribution (see APERTURE illumination,
brightness are reduced. IAM
WEIGHTING).
Ref.: Pereverzentsev (1981), p. 340; Skolnik (1970), p. 6.24.
Bickmore-Spellmire distribution (see WEIGHTING).
A three-dimensional (3D) display is one that shows the
three coordinates of the radar target. To reproduce the third The binomial distribution is the distribution describing the
coordinate implicit techniques are used, making it possible to probability P that j outcomes will take place in n independent
approximate its value. The two basic coordinates are dis- trials when the probability of each outcome is equal to p:
played analogously to the two-coordinate display.
n! j n – j
This display employs a CRT with persistence and a Pj () ---------------------p 1 –= ( p )
j! n – ) !
(
j
bright blip. The 3D display speeds up the operator’s evalua-
Such a distribution describes, for example, the perfor-
tion of the radar situation compared with the use of several
mance of the binary integrator operating with n equal pulses.
two-dimensional displays. IAM
Then P(j) is the probability that exactly j crossings of the
Ref.: Poole (1966), p. 177; Vasin (1977), p. 182.
threshold will occur in n trials if the probability of each
A true-motion display is one “in vehicle-mounted radar that threshold crossing is equal to p. SAL
shows the motions of the radar and of targets tracked by that Ref.: Barton (1989), p. 73.