Transcript Basic Radar Operation - Home

By Terry Sparks
Commander USN Retired
Terry Sparks & Radar
 Navy trained to operate and maintain Radar
 Operated and maintained Radar on 2 US Navy




Submarines
Trained several groups on Radar Operation
Supervised Maneuvering Watch Radar Tracking
BSEE from Washington State
Hold General Class FCC License with Radar
Endorsement
 Test and maintain all transmitting equipment in US
Agenda
 How does Radar work?
 What Can I Expect?
 Controls and Functions
 Contact Avoidance with Radar
 Using EBL and VRM
 Navigation with Radar
Rules of Engagement
I assume there are a lot of different levels of skill here.
 So:
 I will be asking questions as we go through the lesson.
 If you are sure you know the answer, hold back.
 If you know the answer just raise your hand so I will
know who not to call on.
Radar
 GPS can pinpoint your location on earth
 However it is utterly blind to your surroundings
 It can not see:
 Nearby boats
 Squalls & Fog
 Port Entry Hazards
 When charts are not accurate
Radar
 AIS is becoming a poor substitute for Radar
 Great information about ships that have AIS
 Nothing on the rest
 False sense of security
 Tells you nothing about weather
What is Radar
 Acronym: RAdio Detection and Ranging (Radar)
 In use since WWII
 Similar to Sonar, but at a higher frequency
 Radio waves travel at 162,000 nm/Second
 300,000,000 Meters/Second
 Bounce Back from objects
 Time for return is time for 2 times the distance of Object
Radar works on time measurement
Other
vessel
Radar
Antenna
Radar Transmits a pulses then listens for a defined period.
t1
t2
Radar
Pulse
Output
Reflected
Pulse
Arrives back to
Radar
Next Radar
Pulse
Output
Listen period
t1
t2
tMax
For a 26 nm radar tMax is approximately equal to 0.000321 seconds.
~3KHz
Distance to contact = ½ total time X 162,000 nm/Sec
Radio Waves
 HF
 Marine SSB or Ham
 Transmits along the surface of the earth
 Bounces back to earth off the atmosphere
 Could back and forth bounce all the way around the earth
 VHF and UHF
 Marine VHF radio and Ham radio
 Line of site
 Out to Horizon only, then into space
 Radar
 Also Line of site
 Out to Horizon only, plus a small bit
 Then into space
Prospective of the Horizon
 Horizon in NM=
 Distance to the horizon in Nautical Miles
 1.17 X square root Sum of heights

Height of Self + Height of other
 So if you are both at 8 feet
 1.17 X SQRT(8 + 8)
 1.17 X 4
 = 4.68 NM
 50 foot Antenna/Structure at both locations = 11.7 NM
 My antenna at 25’ / 50’ vessel on the horizon = 10 NM
What am I looking at?
 Other vessels less than 10 NM away
 Land can be farther than the 10 NM
 Depending on Elevation
 Weather fronts can be seen beyond the horizon
 Sea return will be strongest around your vessel
 The top of the Radar is normally the bow of the boat.
 It is possible to use true north up (More later)
What am I looking at?
 Display often has fuzzy appearance of contacts
 Navigation Aids look like vessels
 Contacts may appear and disappear
 Things close to each other tend combine
Control and Functions
 Radar Scans 360 degrees about 24 times per minute
 It sends pulses of energy then listens for the echo
 About 3,000 times per second
 4,320,000 pulses per minute
Control and Functions
 Be Careful:
 Some of the controls impact the sensitivity of the
received signal
 Some controls change the display so that it is difficult to
see contacts
Control and Functions
 Tuning – Adjustment of receiver to transmitted
frequency
 Gain – Sensitivity of receiver
 STC – Suppressing Sea Clutter
 Reduces gain near vessel
 A/C Rain – Cuts down on rain return
 Masks small object
 FTC – Suppresses rain clutter from heavy storms
 Masks small object
Control and Functions
 VRM – Variable Range Mark
 ELB – Electronic Bearing Line
 Brill and Tone – Back light and Contrast
 Trail – leaves the last return(s) dimmer for the next
 Rings – Turns range rings on and off
 Off Ctr – Moves vessel to display more information
 Shift forward to see aft more or aft to see forward more
 Also allows other vessel positions on display
Control and Functions
 Tuning – Use Automatic
 Gain – Automatic
 or on highest range adjust manually to just see the noise
 Be careful with STC, A/C Rain, and FTC
 They can reduce a targets visibility
 STC – Keep off or as low as possible
 A/C Rain – Keep off unless needed to see through rain

Contact may still be hidden by rain
 FTC – Keep off unless needed to see through a storm
 Contact may still be hidden by storm
Control and Functions
 VRM – Use to track contacts
 ELB – Use to track contacts & Identify ZERO




BEARING Contacts
Brill and Tone – Adjust to best see the display in
present lighting
Trail – Can help in a congested area to sense where
targets are headed
Rings – Rings are useful and should be on
Off Ctr – Off for sailboats, on for high speed power
Typical
Display
Use of controls - Range
 When off shore, 8 nm may be best range setting
 No More than 10 nm for base, if available
 Change Range several times per hour to all ranges down
to one mile. (Lower the range, the larger the target)
 Expand the range out to the highest range to look for
storm fronts
 Should not be left on 8 nm all the time.
 Contacts may appear very small and be missed
 Plastic and Wood Boats make Poor Targets
Use of controls - Range
 When near land set range only high enough to see the
land
 3 miles off shore, use 3 mile range as base
 When coming into a busy harbor use ½ to 1 nm so
contacts are easily detected
Contacts Size
 The size of a contact is dependent on:
 Range setting
 Gain setting
 Trail on or off
 Type of material for contact
 Metal is better than plastic
 Anti Sea and rain settings will reduce size of target
Selecting a Range
 Need to have response time to correct coarse
 Need to be on low enough range to see contact
 Recreational vessels can be hard to see and move fast
If We Assuming Target Traveling at 25NM/hour
Typical Ranges
Full Scale
Target*
Time to
 0.125
0.3 minutes
0.6 minutes
1.2 minutes
1.8 minutes
2.4 minutes
3.6 minutes
4.8 minutes
7.2 minutes
 0.25
 0.5
 0.75
 1.0
 1.5
 2.0
 3.0
* Target at 25nm/hour
Full Scale
Time to Target*
 4.0
9.6 minutes
14.4 minutes
19.2 minutes
N/A
N/A
N/A
N/A
 6.0
 8.0
 12.0
 16.0
 24.0
 36.0
Range Prospective – 12 miles
000/360
Identify the contacts?
3
270
180
6
9
12
90
Range Prospective – 6 miles
2
4
6
Range Prospective – 3 miles
1
2
3
Our Small Boats
 Maneuver quickly so less time is needed
 Most important is seeing the target
 Even if you have only 7 minutes you can get out of the
way
 @ 5 knots for 7 minutes you can travel 233 yards.
 Or ~700 feet – That would be a real wide ship!
Contact Avoidance with Radar
 When visibility is restricted because of fog, darkness,
etc.
 Radar can help you get through safely.
 Tracking a contact(s) know the Closest Point of
Approach
 CPA(s)
 Priority - Make sure the bearing is changing
 Great Cockpit Calculation – 3 minute rule
3 Minute Rule
Speed in knots, add two zeros * = the Distance
in yards that will travel in 3 minutes
Case 1: Traveling at 5 nm/hr So 5 +00 = 500 yards/3 minutes
Since 2000 yards = 1nm, We travel at 4 * 3 = 12 minutes/nm
Case 2: Own ship 5 knots with other vessel coming head on
at 15 knots 5 miles away!
Solution:
5+15 = 20 nm = 2000 yards /3 minutes.
So we will meet the other vessel in:
3X5 or 15 minutes
* Really Multiplying speed times 100
Relative Bearing vs True Bearing
 On Radar you are normally heading up.
 Relative Bearing (RB)
 Preferred mode for Recreational boats

Corresponds to what you are looking at.
 Possible to use a compass input
 Allows for True Bearing at top of display
 True bearing has the advantage of reducing contact(s)
movement as a result of own vessel heading shifting

but can be confusing when single handing
Relative Vs True Bearing
 Relative Bearing: Heading shifts on own boat results in
contact apparent shifts.
 True Bearing: Not as intuitive as to were contacts are
relative to where you are going.
090
000
Relative Motion
 The contact’s (RB) relative motion is:
 The addition of the direction of the contact and your
direction over the water
 Speed of the contact is also an addition of the two
speeds
 It is actually the vector sum of the two motions.
Relative Motion on a Radar
What is the contacts actual speed and direction?
Contact Relative 5nm VL
Own Ship 10nm VL
Relative Motion on a Radar
What is the contacts actual speed and direction?
Add the contacts
vector to yours
Contact Relative 5nm VL
Own Ship 10nm VL
Relative Motion on a Radar
What is the contacts actual speed and direction?
Contacts true speed
and direction is the
remaining vector
Contact Relative 5nm VL
Own Ship 10nm VL
Relative Motion on a Radar
5kns W
Nav Aid
5knts
5kns N
5kns N
Relative
Motion
On
Radar
Relative Motion on a Radar
What will Each see
On their Radar?
V1 000o at 8 knots
V2 000o at 15 knots
Relative motion of V2 (with respect
to V1) Is at 150o now moving CCW at 7
knots (Being Overtaken)
Relative motion of V1 (with respect
to V2) Is at 320o now moving CCW
at -7 knots (Overtaking)
V1 360o at 8 knots
V2 000o at 15 knots
Relative motion of V2 (with respect
to V1) Is at 150o now moving CCW at
23 knots
Relative motion of V1 (with respect to
V2) Is at 320o now moving CCW at
23 knots
Fast way to find CPA
•If you have a glass screen A grease
pencil is great
•A small clear straight edge is
handy
P2 = 10:30
P1 = 10:00
4
8
12
Fast way to find CPA
P2 = 10:30
CPA
P1 = 10:00
4
8
12
Fast way to find CPA
Where is the CPA?
P1 = 10:00
P2 = 10:30
4
8
12
Fast way to find CPA
P1 = 10:00
P2 = 10:30
CPA
4
8
12
1.
Relative Speed
P1 = 10:00
Calculate Relative Speed
1. Measure distance between P1 &
p2
2. Check against rings
3. Speed = D/t in hours
4. 4nm/0.5 hours = 8nm/hr
2. Measure Distance to CPA = 7 nm
P2 = 10:30
CPA
3. Calculate Time to CPA
1. T = (D/speed X 60 + P2)
2. 7/8 X 60 + 10:30
3. ~11:22
4
8
12
Cockpit Calc
8nm = 800yrds 3 minutes
2.5 periods/nm = 7.5 min/nm
7 miles = 7 X 7.5
7X7 =49 & 7X8 = 56
So it is = 52.5 minutes to CPA
Or about 11:22
What is Wrong?
9.5NM @ 315o
12NM @043o
7.8NM @315o
8.8NM @ 043o
4
8
12
8.5NM @ 129o
12NM @ 129o
7.6NM@ 201o
11.7NM @ 201o
Contacts all on Collision Course
Constant Bearing Rates!
9.5NM @ 315o
12NM @043o
7.8NM @315o
8.8NM @ 043o
4
8
12
8.5NM @ 129o
12NM @ 129o
7.6NM@ 201o
11.7NM @ 201o
Means:
Collision!
Requires Action!
If We Slow or Stop
9.5NM @ 315o
Pass in front!
12NM @043o
7.8NM @315o
8.8NM @ 043o
4
8
12
8.5NM @ 129o
12NM @ 129o
7.6NM@ 201o
11.7NM @ 201o
If We Speed Up
9.5NM @ 315o
Pass Behind!
12NM @043o
7.8NM @315o
8.8NM @ 043o
4
8
12
8.5NM @ 129o
12NM @ 129o
7.6NM@ 201o
11.7NM @ 201o
What Action Here
Come Right and It will
Pass Behind you
9.5NM @ 315o
7.8NM @315o
4
8
12
What About this one?
Come Left and it will
Pass Behind you
12NM @043o
8.8NM @ 043o
4
8
12
What about this one?
Come Right and it will
Pass Behind!
4
8
12
8.5NM @ 129o
12NM @ 129o
Is it Possible
 To have a constant Bearing Rate and no Collision?
 How about 2 vessels traveling in the same direction.
Traveling at the same speed?
19
16
10
18
14
12
17
15
13
11
9
6
0
8
4
27531
Time to get back to Class
Using EBL and VRM
 Older radars have a single set of EBL and VRM
 Newer displays may have several EBLs and VRMs
 EBL = Electronic Bearing Line
 An adjustable line that may be rotated around the
display.
 Typically a dashed line and provides digital display of
distance ring is from center
Using EBL and VRM
 VRM = Variable Range Marker
 An adjustable ring that may be expanded to any distance
on the display
 Typically a dashed line and provides digital direction in
relative degrees
Using EBL and VRM
VRM
EBL
4
8
12
EBL 1 280.1oR
VRM 1 9.42nm
EBL 2
VRM 2
o
R
0.00nm
Setting EBL & VRM to Contact
• Rotate EBL to contact
• Expand VRM rings to Contact
P1 = 10:00
4
8
12
EBL 1 280.1oR
VRM 1 9.42nm
Move Cursor out to Second Point
If it had been a constant
Bearing Rate, the contact
would have walked down
the EBL
P1 = 10:00
+
+
+
P2 = 10:30
+
4
8
12
EBL 1 280.1oR
VRM 1 9.42nm
330.2oR
7.31nm
Lay Ruler across
P1 = 10:00
+
P2 = 10:30
4
8
12
EBL 1 280.1oR
VRM 1 9.42nm
330.2oR
7.31nm
At CPA Now!
P1 = 10:00
+
@cpa
P2 = 10:30
4
8
12
EBL 1 280.1oR
VRM 1 9.42nm
330.2oR
7.31nm
Key Things to Remember
 Target must be able to reflect the radio waves
 Metal reflects best
 Rain will reflect the signal
 Fog will reflect the signal some
 Waves will reflect the signal
Key Things to Remember
 The size of the signal is based on the ability of the
target to reflect the signal
 Not necessarily the size of the target.
 Mark a concerning target with EBL
 If zero bearing change it will walk the line
Practice
 Practice on a clear day so you can compare the Radar
Scans to the real world.
Navigation with Radar
 Navigation is knowing where you are and where you
are going.
 Dead Reckoning Requires Position Fix corrections to
arrive at the planned location.
 Dead Reckoning uses the Compass and Boat speed to
approximate position.
 Direction from compass and Speed X Time for Distance
 Some folks use a hand held GPS for Corrections
 Works good and Fixes are accurate
 What if GPS Goes Away while headed for port?
Navigation with Radar -A Fix
 Need a minimum of two intersecting lines of position
(LOP)
 Radar can provide:
 Multiple Range and bearing LOPs

A single point provides both a bearing and a range
 Two or more Range LOPs
 Two or more Bearing LOPs
Best Accuracy
 Set the radar range for the minimum range to see the
objects to be used
 Can be points of land, light houses, navigation buoys,
etc
 Best fixes come from the best defined objects
The Fix
Nav Buoys
1. Record Bearing, Range, and Time
2. Or two ranges or two bearings
3. Plot on chart
4. Position is at the point of intersection
for the time recorded.
Potential LOPs
2
4
6
The Fix
1. Move cursor to position
2. Record Bearing, Range, and Time
357o
+
+
+
+
Nav Buoy
2
4
6
017.1oR
4.44nm
Another Fix
1. Move cursor to position
2. Record Bearing, Range, and Time
357o
++
+
+
2
4
6
064.3oR
3.91nm
Plotting onto a chart
 To plot on a chart we must have the bearing in True or
Magnetic Bearing
 Easiest in the cockpit is Magnetic Bearing
 We just need to add your heading and not worry about
Magnetic Variation
 Magnetic Bearing is equal to Relative Bearing from
Radar plus your Magnetic Heading
MB = RB + MH
Plotting onto a chart
MB = RB + MH
 Then to plot from the target to your vessel you need
the reciprocal bearing.
To Target
 The bearing on the radar is to the target
 The reciprocal is from the target
 We know on the chart where the target is…
 Reciprocal is +/- 180
o
 So the complete formula for a fix is then:
MB = RB + MH+/-180
From Target
From our targets we then get
MB = RB + MH+/-180
Own Ships
Magnetic
Heading
OR
target
Range NM
target Relative
Bearing
target Magnetic
Bearing
Reciprocal
+/- 180
depending
on value
357
4.44
17.1
374.1
194.1
357
3.91
64.3
421.3
241.3
Subtracting 360 degrees
14.1
194.1
Subtracting 360 degrees
61.3
241.3
Dead Reckoning Plot->
1. Plot bearing lines from target
2. Then draw a range ring across the
Lines from the targets
3. The Fix Point
4. Where we were at the time of the fix!
X
Dead Reckoning Plot->
Using Bearing Only