A paper on

RADAR ANTENNA COMMUNICATION

To
TECHNOBRAIN-2009
AT

ST.JOHNS COLLEGE OF ENGINEERING & TECHNOLOGY

BY
P.UJVALA

V.HARITHA

06481A0477

06481A04A8

III B.TECH

pisipati.ujvala@gmail.com

9248359762

III B.TECH

haritha.veerla@gmail.com

9703921024

FROM

GUDLAVALLERU ENGINEERINCOLLEGE
GUDLAVALLERU

Abstract :
This paper deals with Terminal Doppler

is typically located near to population centers

Weather Radar (TDWR) installed in airports

and congested airspace, so that it is well

to provide wind shear detection services and

situated for supporting weather services for

precipitation reflectivity data to controllers

operationally important areas.

and supervisors. The TDWRs narrow beam

As the name suggests, the Terminal Doppler

and aggressive ground clutter suppression

Weather Radar (TDWR) was purposely built

algorithms

provide

excellent

data

on

to serve the terminal area of the airport. Its

boundary layer reflectivity and winds

in

mission is to detect wind shear and so as to

particular the locations of thunderstorm

enhance the safety of aircraft landing and

outflow boundaries. These data are known to

takeoff. It is located near the airport at a

be essential for providing high resolution

distance of 12 km so that it has a clear view

convective weather forecasts out to two

of the runways, airport approach and

hours. Similarly, its narrow beam could be

departure zones.

useful for detection of severe weather

The TDWR is specially designed to

signatures (e.g., tornado vortices) with small

operate in a high clutter environment

azimuth extent. Relative to the Weather

normally present in the vicinity of airports. It

Service Radar 88-D (NEXRAD) it scans

makes use of a variety of methods to

rapidly (e.g., surface updates once per

minimize clutter and to eliminate the

minute), facilitating monitoring of rapidly

influence of such moving targets as birds,

evolving low altitude wind shear hazards. It

aircrafts.

TDWR ARCHITECTURE

Extension Program (SLEP) to improve

supportability

The TDWR system was designed and built in

the late 1980s, and is encountering issues
related to parts obsolescence. To ensure that
the system continues to be maintainable, the
FAA has commenced a Service. Life

and,

where

appropriate,

introduce improved capability.

A simplified block diagram of the
TDWR is shown in Figure. The RPG
subsystem, shown in green on the upper left,

has recently been re-hosted from a Harris

subsystems. The existing TDWR DSP

Nighthawk UNIX system to one based on a

subsystem hardware consists of a mixture of

pair of redundant SGI Origin computers. The

COTS and custom cards, installed in a single

next major digital subsystem to be addressed,

19 Multibus system chassis. The COTS

and the focus of this paper is the RDA,

boards include a 68020-based single-board

which includes the receiver and DSP

Figure 2. Air Traffic Control Analysis

UPGRADATION OF RADARS
computer (SBC) and a SCSI and serial
controller. The custom components include

WEATHER SERVICE RETIRES LAST

OF OLD RADAR

five boards to handle the A/D interface and

timing needs, eight boards to perform clutter

The new radars are more sensitive, which

filtering, and six boards to handle the

means they can detect more

generation of moments data.

weather details than the old

ones could. also means they

Air Traffic Control Analysis

can detect wind speeds and

The minimum instruments required

directions, giving a much better

under VFR include an airspeed indicator,

picture of bad weather.

altimeter, and magnetic direction indicator.

Minimum

flying

conditions

in

radar-

The new radars make extensive use

controlled airspace in transition areas specify

of computers, which means

a cloud ceiling about 215 m (700 ft) above

they can be programmed to

sound an alarm when weather

ground level and 1.6 km (1 mi)

patterns are beginning to

visibility. Other VFR requirements for

appear dangerous. With the old

visibility and distance from clouds depend

radars, someone had to watch

on altitude and whether operation is in

the screen constantly when

controlled or uncontrolled airspace. VFR

storms were possible to make

flight is not permitted in all airspaces, and

sure nothing important was

terminal control areas sometimes require

missed.

positive (radar) air traffic control. Airport

"It

traffic areas typically encompass a radius of

8 km (5 mi) and are extended laterally for the
control of instrument-dependent departures
and landings. Control zones around airports
extend upwards with no limit.

took

considerable

skill

to

determine storm intensities from green

blotches on the radar scope," said Steve
Rich,

meteorologist-in-charge

of

the

Charleston office. "It took even greater skill

to tell if a storm had tornado characteristics."
Like the user-friendliness built into much of
today's technology, the new Doppler radars

produce highly accurate storm signatures.

"For the first time in history, we are now able
to broadcast a tornado warning for a given
area before a tornado is formed," Rich said.
"This

is

remarkable

technological

achievement and has already saved many

lives.
Figure 3.Doppler Effect

THE DOPPLER EFFECT

"The observed

change in

DOPPLER RADAR AND KEY

the

frequency of sound or electromagnetic

FACTORS FOR UNDERSTANDING

waves due to the relative motions of the

WEATHER RADAR

source and observer."

All weather radars send out radio
The Doppler Effect is best described

waves from an antenna. Objects in the air,

by the change in pitch of a trains whistle as

such as rain drops, snow crystals, hail stones

the train passes by your position. The pitch

or even insects and dust, scatter or reflect

of the trains whistle changes because the

some of the radio waves back to the antenna.

frequency/wavelengths

All

of

the

sound

weather

radars,

including

Nexrad,

increases/decreases as the train moves

electronically convert the reflected radio

toward you and decreases/increases as the

waves into pictures showing the location and

train moves away from you. The same

intensity of precipitation. Doppler radars also

concept applies to meteorological targets.

measure the frequency change in returning

Doppler radar is able to detect the changes in

radio waves. other objects that reflected the

frequency/wavelength resulting from storm

radio

motions toward or away from the radar. This

concept is the basis for all velocity products.
Figure 4.Radar Communication

better

understanding

could

improve

tornado forecasting. In 1995, scientists used

one Doppler radar, nicknamed Doppler on
Wheels (DOW) because it was mobile,
during the At a distance of less than two
miles from a tornado, the Doppler radar
sends out a beam of radio waves to scan the
tornado's wind field. But, with only one radar
researchers can measure only the speeds of
winds going toward or away from the radar.

more

clearly

understand

what's

happening now and what's likely to happen

in the next hour or two
MOBILE RADAR CHASE TARNADOES
Tornado researchers used two
portable Doppler radars on the Plains this
year to obtain even better pictures of what
happens inside tornadoes. This complete
look at tornado-generated winds should
allow meteorologists to fine tune their
conceptual model of tornado structure. Such

radar can measure the wind component in the

direction in which the radar beam is
pointing. Lhermitte and Atlas (1961) first
described how a single Doppler radar could
be used to measure vertical profiles of wind
velocity in widespread precipitation; it can
also be used in clear-air.

Figure6. Tornado Detection by the Radar

Figure 6. Measurement of vertical

profiles of wind by the radar

APPLICATIONS OF TERMINAL

Front location

DOPPLER WEATHER RADAR

Sharp wind shifts, which are frequently

Wind versus height

Meteorological
generally

detect

associated with frontal boundaries, are

Doppler

precipitation

radars
particles,

usually easily identified on the Doppler

velocity display. Thus, fronts can be

insects and refractive index gradients. These

precisely located and their movement closely

scatterers move with the wind. Thus Doppler

monitored on low-level wind shift associated

with a cold front approaching the coast of

abilities to understand and forecast severe

Washington state. In this geographic region

thunderstorms,

accurate frontal locations are rarely known

thunderstorm initiation and to monitor

because data is sparse.

precipitation accumulations. . It is expected

Radar Sees Rain

that as more and more operational Doppler

blizzards,

wind shifts,

radars are installed and a large number of

Rain or snow that evaporates as it

forecasters results will be better its analysis,

falls into a layer of dry air near the earths

forecasting

surface is called virga. While virga can

possible with Doppler radar.

and

warning

applications

happen at any time during the year, it is most

common during winter, when low-level air is

References

very dry. As falling precipitation evaporates

it moistens the dry air from the top down. If

1. www.radarmagzine.com

the precipitation lasts, the air becomes moist

enough to block evaporation and the rain or

2. www.google.com/tdw radar

snow reaches the ground.

3. www.radarsystems.com
4. www.ieee.com

Fig 5 Rain Detection by the Radar

CONCLUSION
The

early

experience

operational

forecasters

88D's

being installed

are

Forecast
that

they

Offices

across

as

the
at
the

of
WSR-

Weather
U.S

is

are able to improve their