tma

Target Motion Analysis

Target Motion Analysis for the Localization of Subsurface Targets

Stephen Haptonstahl

Northern Illinois University

December 3, 1999


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.”


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



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!


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


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


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


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


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


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


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


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


Single-Leg Ekelund

R

x

rateBearing

LOStheacrossspeedTotalR

SASASAR

SARt

x

RtateDifferenti

R

x

ttt

2

2

2

cos

sec

11sec,

tan


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


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


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


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


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


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


The Layer

The sharp temperature gradient at the layer causes most sound to be reflected


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


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?

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