Target Motion Analysis for the Localization of Subsurface Targets

1. Target Motion Analysis for the Localization of Subsurface Targets Stephen Haptonstahl Northern Illinois University December 3, 1999 Target Motion Analysis

2. 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

3. 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

4. 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

5. 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

6. 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 Primary Sources of Information Target Motion Analysis

7. 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

8. TMA Team PC Sharps • 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 TF N Geo-fixed plot Manual Surface Radar TB RT S E Surface/ Subsurface Warfare Supervisor TMA Team Layout on an AEGIS cruiser Target Motion Analysis

9. STI STA STI STI STA STA SOA SOA SOI SOA SOI SOI Line of Sound Line of Sound (LOS): A moving reference line joining ownship and the target Overlead: target and ownship speed vectors on same side of LOS, STA < SOA Lag: target and ownship speed vectors on opposite sides of LOS Lead: target and ownship speed vectors on same side of LOS, STA > SOA Opening: Range increasing Closing: Range decreasing Target Motion Analysis

10. 000 STI STA 090 270 180 Line of Sound – Evaluator’s Plot Purpose: Determine the course and speed of the target Lead Opening Closing Lag Overlead *Expires after ~5 degrees of bearing shift Target Motion Analysis

11. DRT & Geo-fixed PlotRecognizing LOS Geometries Lag Lead Overlead • 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 Max Range Min Range Min spd = ownship spd 6 kts Target Motion Analysis

12. 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 Time-Bearing Plot – Range Calculations Target Motion Analysis

13. Single-Leg Ekelund R  x Target Motion Analysis

14. 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) Target Motion Analysis

15. Applying the Doppler Formula • Assume ownship fixed, or correct for SOI • fcorr increases as STI does Lag Lead Overlead We have yet to see his bow (nose), so STI is increasing Our view or him is shifting more toward his stern (tail), so STI is decreasing Target Motion Analysis

16. Line of Sound Determination Target Motion Analysis

17. 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

18. 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

19. 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

20. The Layer The sharp temperature gradient at the layer causes most sound to be reflected Target Motion Analysis

21. 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

22. 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? Target Motion Analysis