target motion analysis target motion analysis for the localization of subsurface targets stephen...
TRANSCRIPT
Target Motion Analysis
Target Motion Analysis for the Localization of Subsurface Targets
Stephen Haptonstahl
Northern Illinois University
December 3, 1999
Target Motion Analysis
Disclaimer or How Different Cultures Say“I don’t know”
Politician: “We have a Congressional committee investigating that issue.”
Programmer: “You can’t do that in Windows. That only works in UNIX.”
Consultant: “I can provide that information, but it will cost you more.”
Military: “I’d tell you, but it’s classified, so then I’d have to kill you.”
Math student: “We never talked about that in class.”
Math Professor: “That’s beyond the scope of the course.”
Target Motion Analysis
The Company: Your Country
• US Navy– 369,220 sailors in uniform (1 officer/6 enlisted)
• Who joins the Navy?
– 316 Ships & Subs – almost half underway– Operating in every part of the world
• Other branches– Total # of people
• Allied forces– # of other nations
Target Motion Analysis
Target Motion Analysis
Strategy: Prevent enemy submarines from getting close enough to destroy your ship
Tactic: Keep the sub “occupied” dodging helicopter-launched torpedoes.
Problem: Where do you send your helicopter?
The Captain wants an answer in 30 minutes!
Target Motion Analysis
Describing Location in Maritime Warfare
• Bearing and Range from ownship - polar coordinates– Bearing (BRG): Compass direction (true, not magnetic) from ownship
to target in degrees (“mills” used in gunnery – 6400 mills = 360º)
– Range (RNG): Distance to target in yards or nautical miles
– Relative reference frame – must correct for ownship motion to get true (WRT Earth) motion
• Latitude (N-S) and Longitude (E-W)– Geo-fixed reference frame
• Nautical Mile (NM)– Defined to be 1/60 degree latitude (equator to pole:=5400 NM)
– Equal to about 6000 feet, 2000 yards, or 1.1 statute mile
Target Motion Analysis
Primary Sources of Information
• Active sonar– Bearing, range, perhaps
depth of target – course and speed
– Very limited range
– Counterdetection (perhaps 10X sonar range)
– Amorous marine life
• Passive sonar– Greater range
– No counterdetection issues (other that normal)
– No range information – no course and speed
– Must use TMA to get range, course, speed
Target Motion Analysis
Other Sources of Information
• Visual – periscopes leave wakes– Lookouts (ours or on other ships) (BRG & est. RNG)– Pilots (est. lat & lon)
• Sonobuoys– “Yardstick” – range from buoy– “Pointer” – bearing from buoy– “Cadillac” - both
• MAD – Magnetic anomaly detector– Very short range, but can’t mistake a whale for a sub
• EW - Reception of their radar or radio emissions – BRG only• Intelligence
– SOSUS – Sound Surveillance System– Various classified sources
Target Motion Analysis
TMA Team
• Composition– Evaluator– South & North Plotters– Time/Bearing Plotter– Time/Frequency Plotter– R/T talker and Sharps
• Input– Sonar/EW/Intel– Priorities set by CO
• Output– Location of targets– Course/speed
recommendations
Geo-fixedplot
Surface/Subsurface
WarfareSupervisor
ManualSurfaceRadar
S
N
E
TF
TB
Sharps
RT
PC
TMA Team Layout onan AEGIS cruiser
Target Motion Analysis
Line of SoundLine of Sound (LOS): A moving reference line joining ownship and the target
STA
STI
SOI
SOA
Lag: target and ownship speed vectors on opposite sides of LOS
STA
STI
SOI
SOA
STA
STI
SOI
SOA
Lead: target and ownship speed vectors on same side of LOS,
STA > SOA
Overlead: target and ownship speed vectors on same side of LOS,
STA < SOA
Opening: Range increasing Closing: Range decreasing
Target Motion Analysis
Line of Sound – Evaluator’s Plot
Purpose: Determine the course and speed of the target000
180
090270 Lag
Lead
Overlead
Opening
Closing
*Expires after ~5 degreesof bearing shift
STI
STA
Target Motion Analysis
DRT & Geo-fixed PlotRecognizing LOS Geometries
• Input: almost everything • Speed strips – get course, speed, range• This is where all the information is compiled, where the Captain will look for a
picture of what’s going on
MinRange
Lag OverleadLead
MaxRange
Min spd = ownship spd
6kts
Target Motion Analysis
Time-Bearing Plot – Range Calculations
• CPA at graph inflection point – convexity determines whether
opening or closing
• Single-leg Ekelund– Doesn’t require ownship
maneuver– Requires an estimated STA
• Double-leg Ekelund– Uses info before and after
ownship maneuver– Yields accurate range at a time
near the maneuver– Often target’s relative motion
allows this technique
• Spiess– Useful when target has low
bearing rate (<1º/min) (not common)
– Cross-fix using only one ship
Target Motion Analysis
Single-Leg Ekelund
R
x
rateBearing
LOStheacrossspeedTotalR
SASASAR
SARt
x
RtateDifferenti
R
x
ttt
2
2
2
cos
sec
11sec,
tan
Target Motion Analysis
Doppler Effect – Time-Frequency Plot
• Using rt = d, we can determine the perceived change in frequency caused by STI & SOI– Sw = Speed of sound in sea water, 1664 yds/sec– SI = STI + SOI– fr = received frequency– f0 = emitted frequency– fcorr = f0 affected only by target motion
• Plot fr, then calculate SOI to get fcorr
• Changes in fcorr are caused by– Changes in STI caused by shifting LOS geometry– Target maneuvers (best way to detect target maneuvers)
wr
w
rw
w
wr
Sf
fSI
SIS
fSf
fS
SISf
1
)(
0
0
0
Target Motion Analysis
Applying the Doppler Formula
• Assume ownship fixed, or correct for SOI
• fcorr increases as STI does)(')('
)()(
0
00
tISS
ftf
ftISS
ftf
Tw
corr
Tw
corr
Lag Lead Overlead
Our view or him is shifting more toward his stern (tail), so STI is decreasing
We have yet to see his bow (nose), so STI is increasing
Target Motion Analysis
Line of Sound Determination
Lines on Geo-fixed
plot
Fcorr
(f0 plus STI)LOS
Geometry
Get from Geo-fixed
plot
Don’t cross Decreasing Lead Min speed
Cross Decreasing Lag Min range
Cross Increasing Overlead Max range
Target Motion Analysis
What If We Know the Target’s Speed?
• Sources– Blade count + ID of class = speed– Intelligence
“We believe a Kilo is transiting from Murmansk to Cuba over x days, so expect a minimum speed of y knots.”
– Geo-fixed plot (speed strips; lead geometry)
• What we get– If we have max(fc) (perhaps a natural transition from overlead
to lag) then we can get f0
– Evaluator can improve LOS diagram to better estimate course– Geo-fixed plot can accurately fix strips to get course and
range
Target Motion Analysis
What If We Know the Emitted Frequency (f0)?
• Sources– Inflection point of fc
– “Crazy Ivan” (like in Hunt for Red October): Target turns through 360º to check for contacts in his baffles (wake). We get f0 halfway between max(fcorr) and min(fcorr). Also get contact speed.
• We get– Very accurate course– Warren (freq) range
Target Motion Analysis
Water is Thicker than VacuumConvergence Zones
• Sound moves along paths of least resistance• Salinity, temperature and pressure all change with depth
and affect sound propagation• Balance struck is a set of distinct solutions, each a path
Target Motion Analysis
The Layer
The sharp temperature gradient at the layer causes most sound to be reflected
Target Motion Analysis
Technology on the Horizon
• Expert systems – AI based TMA– Can we do it?– Is it a good idea?
• Bottom bounce– Multiple instances of the same sound coming in at slightly
different times from different angles
• Ambient noise– We see with ambient light, why not apply this idea to
sonar?
• Improved active sonar has reduced counterdetection range
Target Motion Analysis
Advanced Techniques and Further Questions
• Tactics– What are good maneuvers to recommend that will:
• Maximize information on the target
• Minimize counterdetection – Zigzag plans
– EMCON
– How do we respond to target maneuvers?
• What’s the best we can do with these formulas? Can we get more from less?