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Helping to keep the skies safe . . .
by
Dr David Maddison
Airborne Weather Radar
Airborne Weather Radar enables flight routing to avoid extreme weather
in order to keep passengers and crew safe and more comfortable – and
to avoid damage to the aircraft. Huge advances have been made in this
technology in recent years, including Rockwell Collins new “MultiScan”
ThreatTrack Radar, released only last year at the Singapore Airshow.
D
espite the fact that flying is the safest way to travel,
the year 2014 was perceived by many as a bad year
for aviation – although that really depends upon
how you analyse the statistics.
According to the Geneva-based Bureau of Aircraft Accidents Archives (BAAA) there were 111 aircraft accidents
in 2014, the lowest number of accidents since 1927. The
BAAA counts any aircraft crash in which the aircraft is
certified for at least six people plus the crew. It also counts
shoot-downs but does not count military aircraft except
troop carriers and other aircraft that can carry more than
six passengers.
Deaths are a different matter, however and 2014 saw
1,328 people die in aircraft crashes and shoot-downs, the
most since 2005, according to BAAA statistical methods.
Cause
1950s 1960s 1970s 1980s
Pilot Error
42
36
25
29
Pilot Error weather related
10
18
14
16
Pilot Error mechanical related 6
9
5
2
Total Pilot Error
58
63
44
57
Other Human Error
3
8
9
5
Weather
16
9
14
14
Mechanical Failure
21
19
20
21
Sabotage
3
5
11
12
Other Cause
0
2
2
1
1990s 2000s Average
29
21
5
55
8
8
18
10
1
34
18
5
57
6
6
22
9
0
32
16
5
53
6
12
20
8
1
Fatal accident causes for commercial aircraft with 19 or
more passengers on board from 1950 to 2010. Over that
period weather-related fatalities, both involving and not
involving weather-related pilot error have been a factor in
28% of accidents. (www.planecrashinfo.com/cause.htm).
16 Silicon Chip
However, according to the Aviation Safety Network (which
counts only civilian planes which are certified for 14 passengers or more and does not count corporate jets, shootdowns or sabotage) in 2014 there were 692 people killed in
aircraft incidents making it the safest year since 1945. This
would obviously exclude the 298 killed when Malaysian
Airlines flight MH17 was shot down over the Ukraine.
According to the BAAA there were 163 weather-related
fatalities in 2014 and 162 of those were on Air Asia flight
QZ8501 that crashed into the Java Sea off Indonesia. The aircraft was an Airbus 320-200. Historically, weather-related
aircraft fatalities due to crashes are a factor in 28% of cases.
Avoiding weather of sufficient severity to put an aircraft
Adverse weather effect on an aircraft: a lightning strike.
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World’s first airborne weather radar – the ECKO airborne
“cloud and collision warning search radar” from 1950.
at risk is of particular importance. Planning to avoid potentially dangerous weather starts at the flight planning stage
but after take-off weather continues to be monitored both
from reports radioed to the aircraft and on-board weather
monitoring systems, the most important of which are the
pilot’s Mark I eyeballs!
Some aircraft operating in some areas also transmit
weather data to meteorological authorities where it is fed
into weather models to supplement data from weather
balloons and other sensors.
Apart from the possibility of severe weather causing fatal
aircraft crashes, a much more common occurrence is injury
to passengers and damage to aircraft caused by turbulence.
In order to assist aircraft operators avoid bad weather
once in flight they use aircraft mounted weather radar
systems (radar is an acronym for RAdio Detection And
Ranging).
Airborne weather radar detects bad weather in the
aircraft’s flight path and allows the pilot(s) to avoid the
worst of it.
Another primary purpose of airborne weather radar is
to ensure that course deviations to avoid bad weather are
kept to the minimum that is necessary to avoid the adverse
weather, without adding excessively to the distance to be
flown which increases the time taken and adds to operating costs.
A problem?
The ability for radar to detect weather conditions was first
noted during World War II where it was seen as a problem
as radar returns from certain weather systems containing
rain, snow and sleet could mask enemy activity. Ways were
then developed to filter out such undesirable returns but
scientists and engineers started studying the phenomenon
after the war as a means to monitor weather and it has been
extensively developed ever since.
The first airborne weather radar was from the UK company ECKO who, in 1950, developed the “cloud and collision warning search radar”.
In later developments in 1953 a researcher with the Illinois State Water Survey produced the first radar image of
a “hook echo”, a particular type of weather radar signature
associated with tornadoes. This demonstrated the viability
of using radar to detect severe weather conditions and even
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The first weather radar image of a “hook echo” which is
associated with tornadoes, taken in 1953.
provide early warning of developing severe conditions.
Early ground-based and airborne weather radars provided
information on the reflectivity of whatever targets they illuminated but could give no information on the speed, of
say, water droplets in a storm which would be indicative
of wind speed.
Initial research on weather radar systems focused on
observations of the precipitation within a weather system
and its development, movement and structure, as well as
making observations of the relationship between the characteristics of the radar echo and precipitation rate. When
there was a greater precipitation rate there were more water
droplets for the radar beam to reflect from and therefore
the radar return was greater.
Doppler radar for weather
In 1950s research began on Doppler radar for weather
applications although the earliest Doppler radar systems
were developed during World War II.
The Doppler effect is the familiar property of a moving
noise source such as a siren changing in frequency as it
approaches an observer and then moves away. The same
phenomenon applies to radar signals whose return echo is
influenced by the velocity of the target they are bouncing
off, such as rain drops.
Early Doppler radars used large and sensitive analog
filters and were not practical for airborne operation except
under special circumstances. It required the development
Feet, Nautical Miles & Flight Levels
While Australia (and indeed most countries) have
adopted the metric system, in aviation Imperial units are
still used: heights are generally expressed in feet, distances
in nautical miles and speed in knots (which is of course
nautical miles per hour).
You may also come across the term “flight level” with
values between zero and perhaps 500. While a flight level
strictly speaking is a barometric pressure (based on an international standard air pressure at sea level), it is conveniently used to express a height above sea level expressed
in thousands of feet. Therefore an aircraft said to be flying
at flight level 360 means it is 36,000 feet above sea level.
April 2015 17
VISUAL TOP
RADAR TOP
A primary threat to en-route weather
avoidance is the fact that thunderstorm cell
tops are non-reflective because they contain
ice – a poor radar reflector.
of fast computers and digital signal processing in the 1970s
and the development of digital Doppler radar to enable
useful and easy to visualise weather information to be interpreted from such Doppler shifts in the return radar echoes.
As an aside, it is interesting to note that an unexpected
Representative values of radar reflectivity as a function of
height for equatorial oceanic and continental geographical
areas and mid-latitude areas. For a given cruise altitude
of 35,000 feet note the very large variation of reflectivity
between the equatorial oceanic (black vertical bar) regions
and the mid-latitude continental (yellow vertical bar)
regions, corresponding to almost a 20dB range or 100
times power ratio. Note also the dramatic loss of radar
reflectivity above the typical altitude for freezing of water
at 16,000 feet. dBZ is a a logarithmic measure used for
radar systems representing the radar echo intensity.
(Diagram courtesy Rockwell Collins.)
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problem during the development of early radar systems
was that the Doppler shift induced by the reflection of a
radar pulse from a fast moving object effected a phase shift
in the returning signal, causing the signal to be cancelled
and thus reverse phase-shift compensation had to be built
into the radar set.
The development of Doppler radar enabled not only the
shape and location of a weather pattern to be determined
but also the velocity of precipitation within that weather
pattern, and by inference, wind speed. Doppler radar also
allows the elimination of returns travelling at a particular
velocity. For example, with airborne radar, ground returns
can be eliminated.
Airborne weather radar can be classified as either the
more conventional and familiar two dimensional radar,
or the more recently developed three dimensional radar.
It might also come as a surprise to some that modern commercial aircraft do not have general purpose radars that
indicate the presence of other aircraft or terrain. Avoidance
of these is effected by pilot observation, flight planning,
transponders on aircraft and automated aircraft systems.
What you see is not what you get!
Monitoring weather systems with radar might seem
straightforward but there are many complicating factors.
For a start, what is visible to the naked eye may not be visible to radar. For example, the cloud tops of thunderstorms
contain mainly ice and that is a very poor radar reflector.
Typically, above 16,000 feet the temperature will be
below zero centigrade and so water will be in the frozen
state. The cloud top will be visible to the naked eye but
not to the radar, or there will be very poor radar visibility
so the flight crew have to correlate in their mind what
they see with their eyes and how that relates to the radar
information being received.
As a general rule, the lower two thirds of a cloud are visible to radar and the top one third is invisible, due to the
presence of non-radar-reflective ice crystals. Of course, even
though the cloud top may be invisible to radar it does not
mean it is not of concern and there can be turbulence within
that area of the cloud which can affect flight operations.
The presence of certain weather patterns that are visible
to the radar below 16,000 feet can be used to infer that there
will be certain formations above them and what their properties may be. This important point will be discussed later.
By convention, a display for weather radar is coded by
three different colours according to precipitation activity.
Green or Level 1 refers to light precipitation activity, little
or no visibility and possible reduced turbulence; yellow
or Level 2 corresponds to moderate precipitation, very low
visibility, moderate turbulence and passenger discomfort;
while red or Level 3 refers to heavy precipitation, possible
thunderstorms, severe turbulence and the possibility of
aircraft damage. Black corresponds to no return. A typical
cloud will have heaviest precipitation at the bottom, with
less higher up in the cloud.
It should be noted that the radar reflectivity varies enormously for different types of weather and is dependent on
several factors. Mid-latitude continental thunderstorms
have a much greater radar reflectivity than, say, equatorial
oceanic thunderstorm clouds. This has lead to problems in
the past as a weather radar might be optimised for typical
weather conditions in, say, the United States where it is
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manufactured and where most of its planes fly (mid-latitude
continental area) but it would not work so well for an
Australian operator in areas where many of its planes fly
(equatorial oceanic). In fact the variation in radar return
from these two types of conditions may vary by a factor of
20dB or 100 times (see graph).
Some examples of the different radar characteristics of
thunderstorms are as follows: continental land-based thunderstorms (eg, USA) typically have high moisture content at
high altitude and are more radar reflective than other types.
Oceanic thunderstorms (eg, Bay of Bengal) have low radar reflectivity as their moisture is located at low altitudes
and the cloud tops are invisible to radar. Mid-latitude land
based thunderstorms (eg, Brazil) have an intermediate
radar reflectivity between that of continental land-based
thunderstorms and oceanic thunderstorms.
In addition to geographical variation in the radar reflectivity of storms, there is also a seasonal variation. An
additional problem is how to determine the severity of a
thunderstorm cell. They may look the same to the eye and
on the radar but one might be much more risk for hail and
lightning than the other. Thus it is clear that a weather
radar should ideally take all these factors into account.
When monitoring weather patterns from aircraft it is
important to get a complete view of meteorological activity.
With conventional 2D airborne weather radar the image provided is in one field of view like a slice and so the flight crew
have to manually tilt the radar beam up and down to get a
full picture of the weather. There is a fairly significant flight
crew workload associated with obtaining comprehensive
weather information with 2D radar. For an instruction guide
on the operation of a typical
modern 2D airborne weather
radar you may
wish to see the
video “EJETS
WEATHER RADAR OPERATION” http://
youtu.be/VusX0V2zvU8
Ground-based
weather radar
For those interested,
there are numerous
weather-related websites
along with radar Apps for
smart phones.
We featured the Australian
Bureau of Meterology Doppler
Weather Radar in the January
2010 issue (also see www.
bom.gov.au/australia/radar/
3D Radar
or www.weatherzone.com.au/
I n r e c e n t radar/, among others).
times two companies have
developed
airborne 3D
weather radar.
One company
is Honeywell
with their IntuVue RDR-4000
system and the other company is Rockwell Collins with
their WXR-2100 MultiScan ThreatTrack system. The objective with 3D radar is to reduce flight crew work load and to
provide a more comprehensive picture of weather activity.
This leads to greater safety and airline efficiency.
The Honeywell system is currently used on the Boeing
737NG, 777, C-17, and Airbus A380 aircraft and has been
A typical MultiScan radar display showing various weather threats.
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April 2015 19
A typical MultiScan
display and how
it correlates with
what is seen out
of the cockpit
windows.
selected for the Airbus A350, Gulfstream G650 and KHI
CX aircraft platforms.
Rockwell Collins system
The Rockwell Collins system has been installed on all
Qantas aircraft, and is standard on all new Boeing 787
Dreamliners, Boeing 747-800s and Boeing Business Jets
and is an option for the Airbus A320s, A330s and A340s,
and Boeing 777s and Next-Generation 737s.
Qantas is a pioneering operator of the Rockwell Collins
Milestones in radar development
1865 James Clerk Maxwell publishes “A Dynamical Theory of the
Electromagnetic Field” with the original four Maxwell’s Equations
which describe how electric and magnetic fields are generated
and relate to each other.
1887 Starting in November of that year, Heinrich Rudolf Hertz
discovers electromagnetic waves, proves Maxwell’s Equations
and publishes a series of papers, the first being “On Electromagnetic Effects Produced by Electrical Disturbances in Insulators”.
1899 Guglielmo Marconi recalls his 1899 work in 1922 and says
a “ship could radiate or project a divergent beam of these
[electromagnetic] rays in any desired direction, which rays, if
coming across a metallic object, such as another steamer or
ship, would be reflected back to a receiver screened from the
local transmitter on the sending ship, and thereby immediately
reveal the presence and bearing of the other ship in fog or thick
weather.”
1900 Nikola Tesla in Century magazine wrote “by their [standing
electromagnetic waves] use we may produce at will, from a
sending station, an electrical effect in any particular region of
the globe; [with which] we may determine the relative position or
course of a moving object, such as a vessel at sea, the distance
traversed by the same, or its speed.”
1904 Christian Hülsmeyer demonstrates detection of a ship at a
distance with his “Telemobiloskop” and is sometimes credited
with the invention of radar but it does not give the range of
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an object direct. It is the first patented device that can detect
objects at a distance.
1917 Lucien Lévy invents the superheterodyne receiver.
1921 The magnetron is invented by Albert Wallace Hull.
1922 US Naval Research Laboratory engineers Albert H. Taylor
and Leo C. Young detect a wooden ship in the Potomac River
by accident when conducting communications experiments and
later in 1937 develop a practical ship-based radar.
1930 Lawrence A. Hyland at US Naval Research Laboratory demonstrates the reflection of radio waves from an aircraft.
1936 The development of the klystron at General Electric by George
F. Metcalf and William C. Hahn (the invention has also been attributed to the brothers Russell and Sigurd Varian of Stanford
University in 1937).
From this time on radar was rapidly developed, especially as the
Second World War loomed and was soon started.
For more details on the history of radar you may wish to look at
http://en.wikipedia.org/wiki/History_of_radar Some YouTube
videos of interest are:
“Radar: Technical Principles: Mechanics” pt1-2 1946 US Army
Training Film” http://youtu.be/64LUeQ4DAqg and “Heroes
and Weapons of WWII : 01. The Men Who Invented Radar”
http://youtu.be/5x37BVCvFRk
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Rockwell Collins WXR-2100 as installed in aircraft cockpit and displayed on the central monitor.
system and has been using it since it was first released to
the market in its original version in 2002. In fact, Qantas
played a major role in its development. Qantas flies across
the Pacific Ocean frequently, often at night and thus had
a particular incentive to want better weather radar than
Air Turbulence
In Australia, there are about 25 in-flight turbulence related
injuries every year according to the Australian Transport
Safety Bureau (ATSB) with many more unreported. Some
injuries are serious with broken bones and head injuries. In
a typical severe turbulence event, 99 percent of passengers
will not be injured.
Since Australia has some of the best flying conditions in the
world, it is expected that flights outside of Australia will encounter more serious problems than flights within Australia.
From 2009 to 2013 there were 677 turbulence related instances reported to the ATSB on flights to and from Australia
with 197 minor injuries and 2 major injuries.
Australia’s Civil Aviation Safety Authority (CASA) classifies several types of turbulence and their causes as follows.
Types of turbulence
Light turbulence - briefly causes slight, erratic changes in
altitude and/or attitude.
Light chop - slight, rapid and somewhat rhythmic bumpiness
without noticeable changes in altitude or attitude.
Moderate turbulence - similar to light turbulence, but greater
intensity. Changes in altitude/attitude occur. Aircraft remains in control at all times. Variations in indicated air
speed.
Moderate chop - similar to light chop, but greater intensity.
Rapid bumps or jolts without obvious changes in altitude
or attitude.
Severe turbulence - large, abrupt changes in altitude/atsiliconchip.com.au
conventional 2D weather radar which requires a lot of
flight crew interpretation and represents a high work load.
While both Honeywell and Rockwell Collins make superb radar systems, the Rockwell Collins system has an
Australian connection and it is the focus of the remainder
titude. Large variation in indicated airspeed. Aircraft may
be temporarily out of control.
Extreme turbulence - aircraft is violently tossed about and
is impossible to control; may cause structural damage.
The causes
Thermals - Heat from the sun makes warm air masses rise
and cold ones sink.
Jet streams - Fast, high-altitude air currents shift, disturbing
the air nearby.
Mountains - Air passes over mountains and causes turbulence as it flows above the air on the other side.
Wake turbulence - Near the ground a passing plane or
helicopter sets up small, chaotic air currents.
Microbursts - A storm or a passing aircraft stirs up a strong
downdraft close to the ground.
Preventing injury from air turbulence
Occasional injuries are sustained by passengers due to
air turbulence, mainly by being thrown about the cabin or
by having items fall on them from open overhead lockers.
Almost all air turbulence related injuries can be avoided
by ensuring objects are securely placed in overhead lockers
and the lockers are kept closed and that seat belts are worn
at all times, not just during take off and landing.
Also, crew instructions should be followed at all times and
you should familiarise yourself with the safety information
card in the seat back pocket.
April 2015 21
Rockwell Collins MultiScan ThreatTrack
Radar – features and development
milestones
2002 Release of first model and it is put into immediate
service by Qantas. This version was called MultiScan.
2003 On delivery flights of Qantas aircraft from the USA
to Australia the flight time was used to test and develop
the next version of the system. The aircraft flew with
both a certified version of the radar and also the test
unit. Data obtained were eventually incorporated into
the 2008 model.
2006-2007 Rockwell Collins rented a Boeing business jet
and flew around the world for three months to verify
what was learned during the Qantas flights and this
information was incorporated into the 2008 model.
2008 A major upgrade was made from the 2002 model.
Storm top prediction was possible due to the addition
of a geographic database of storm models in different
areas at different times of the year. This was called
MultiScan VI.
2014 Hail and lightning detection was added (predictive
overflight). The ability to track 48 different thunderstorm cells and vertical analysis of thunderstorm
cells were added. This version was called MultiScan
ThreatTrak.
Note that the essence of the radar system is in its
smart software, it represents a revolution in software
rather than a revolution in hardware. Earlier model systems can be upgraded to the current specifications by
software upgrades and some minor hardware changes
in some cases.
Windshear is a hazard pilots dread because in the vast
majority of cases they receive no visual warning of the
phenomenon. Here the red and black stripes represent the
actual windshear location along with a warning reminder
at upper right.
22 Silicon Chip
of this article but the same general principles apply to the
Honeywell system.
A video of the Honeywell IntuVue radar is available at
“IntuVue® 3-D Weather Radar” http://youtu.be/w8IYyFmJcF0 and a training video for its use “RDR-4000 IntuVue™
Weather Radar Pilot Training for Boeing Aircraft | Avionics | Honeywell Aviation” http://youtu.be/WNVtJeccNSM
A video of the MultiScan radar can be seen on YouTube
at “MultiScan ThreatTrack weather radar -- The worst
weather is the one you can’t see coming” http://youtu.
be/zJDduGPvOEA and Boeing crew training videos can
be seen at “MultiScan Weather Radar Module 1 Boeing”
http://youtu.be/EUjxFVRTdtw and “MultiScan Weather
Radar Module 2” http://youtu.be/Ai_P-MwlrOw
The Rockwell Collins MultiScan ThreatTrack has the
following technologies:
Geographic Weather Correlation: Recall from earlier
in this article that there is significant regional variation
in the radar reflectivity of thunderstorm cells as well as
variation according to the time of year. This is a relatively
recent discovery that occurred from 1997 onwards after
the launch of the TRMM satellite (Tropical Rain Forest
Measuring Mission).
This satellite has amassed a vast database of thunderstorm
reflectivity information which, along with the work of leading climatologist Dr Ed Zipser, has enabled Rockwell Collins
to embed thunderstorm models into the radar which are
specific to particular geographic locations and time of year.
As previously noted, the tops of storm clouds are invisible
to radar but the radar model is able to make predictions of
the altitude of the true top of the storm cell and its level of
hazard by knowing the location and time of year.
Core Threat Analysis: The radar can track up to 48
thunderstorm cores at once and also predict their severity.
Automatic Temperature-Based Gain: As the outside air
temperature decreases, the cloud tops become less radar
reflective so this feature increases the radar energy used to
This particular windshear occurred during taxiing. In these
pictures from the cockpit the windshear can be seen in the
form of a line squall approaching the aircraft down the
taxiway. The pilot delayed his takeoff for 30 minutes until
the thunderstorm had passed the airport and took off safely.
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illuminate the cloud, effectively decreasing the proportion
of the cloud that is invisible to radar.
OverFlight Protection: Traditional manual operation of
2D weather radars involves pointing the radar beam at the
lower radar reflective portion of storm clouds. As a matter
of simple geometry, if no adjustment to the beam angle is
made, as the aircraft approaches the cloud the beam moves
higher and higher until it is in the non-reflective part of
the cloud and the storm cell disappears from view. The
overflight protection feature keeps the beam pointed 6,000
feet beneath the flight path to keep the reflective portion
of the cloud in view.
Predictive OverFlight Protection: Storm cells can grow
at up to 6,000 feet per minute and when this happens a
“bubble” of turbulent air is pushed above the cloud top.
This feature tracks the rate of growth of storm cells and
warns if there is a fast-growing cell in the vicinity, which
is to be avoided.
SmartScan: As an aircraft turns with traditional radar
there is a black wedge indicated a lack of data in the direction of the turn. This feature ensures that data is immediately acquired in the direction of the turn.
Two Level Enhanced Turbulence: USA FAA regulations require turbulence with a ±0.3G RMS severity to be
displayed on weather radars but in addition to displaying
that, areas with a less severe but still uncomfortable level
of turbulence are also displayed.
Flight Path Hazard Assessment: The radar system looks
for different hazards according to those relevant to the
phase of flight.
For example during take off and landing the main concern is storm cells with convective activity and the Core
Threat Analysis feature is used to evaluate the threat;
during cruise the main threat is accidental penetration
of thunderstorm cloud tops, so the Geographic Weather
Correlation, Automatic Temperature Based Gain and the
Predictive Overflight Protection features are invoked to
prevent flying through the cloud tops.
In addition to these features there is also a wind-shear
alert and an attenuation alert to warn when a storm cloud
has absorbed so much radar energy that nothing behind it
will be visible (radar shadow).
Quiet, dark cockpit
In keeping with modern aircraft flight philosophy of
minimising the pilot workload (the “quiet, dark cockpit”)
the MultiScan radar ensures that only relevant information
is displayed. Threatening weather can be detected out to a
maximum range of 320 nautical miles while non-threatening weather 6,000 feet beneath the aircraft is not displayed.
In order to minimise the display of unnecessary information ground clutter is removed by the use of a global terrain
model so that returns from the ground can be ignored.
With so many aircraft flying around the world, many
fitted with the same model of radar, one might wonder if
there is potential for the radars to interfere with each other.
This is not a problem as each radar pulse is sent out
with a slightly different frequency and the radar will reject
any pulse it receives that is not at the frequency that was
sent out.
The radar dish for this system is around 70cm in diameter and sweeps side to side and up and down every four
seconds.
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Radar and the pulse repetition
frequency and Doppler
compromise
Traditional radar works by sending out a short
signal pulse and then turning off the transmitter and
listening for any signals reflected back to the radar
antenna. Knowing that the radar signal travels at the
speed of light, it is possible to determine the distance
to an object, by dividing the total time for the pulse to
return by two.
The required length of the period between pulses
has to be enough time for the signal to travel out from
the radar set to the target object and return. A long
period between pulses allows objects to be seen at
a long distance compared to a short inter-pulse period which will only allow objects to be seen a short
distance away.
A compromise short inter-pulse period, corresponding to a high pulse repetition frequency (PRF) allows
a potential target to be illuminated with more radio
energy. This makes an object easier to see than if
illuminated with a low pulse repetition frequency.
However, a low pulse repetition frequency is needed
if distant objects are to be observed and they are
illuminated with less radio energy due to a lower
number of pulses.
In fact, the energy reflected from the target back to
the transmitter is also subject to the inverse square
law so the energy received back at the radar set has
a fourth root dependence, not a square root dependence. A consequence of this is that to double the effective range of a radar system the power has to be
increased by a factor of 16.
With Doppler radar there is a further compromise
which is that there is an inverse relationship between
the distance that the radar can see to and the velocity
that can be measured. When the PRF is low a long
distance can be measured but only a low range of velocities. When the PRF is high, a much higher range of
velocities can be measured but the range is reduced.
A more recent development in radar, at least as
far as commercial augmentation is concerned, is
Frequency-Modulated Continuous Wave, or “Broadband” Radar, which unlike traditional radar doesn’t
use a high-energy pulse but is “always on”. Contradictory though it may sound, FMCW radar uses a lot
less energy, is a lot safer to operate close to and is
particularly applicable to marine use (see the feature
in November 2010 SILICON CHIP).
Conclusion
Great advances have been made in radar since it was
first invented. The most recent advances are being made
not so much in radar hardware but in the software used to
interpret and make use of the radar data.
As applied to airborne weather-radar, recent developments in 3D radar which serve to both reduce pilot work
load and greatly increase the analysis of weather systems
and the possible threats posed will make our skies even
SC
safer than they are now.
April 2015 23
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