1. Track-While-Scan (TWS)
Naval Weapons Systems
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2. Learning Objectives Comprehend concepts of TWS system
Know the six basic functions of a TWS system
Comprehend the concepts of acquisition, tracking, and turning gates

3. Limitation of Traditional Search Radar:
NO FIRE CONTROL SOLUTION

4. Problems Dedicated FC radar can only track one target.
Systems usually have separate Scanning and Tracking Radars.
The target knows it’s being tracked.
The target can initiate Counter Measures
Weapons home in on FC radar
EP = Electronic Protection
EA = Electronic Attack
[ ...and then ES = Electronic Support ]

5. Concept of TWS Maintain Target tracks in a computer
Periodic updates from a scanning radar
1. Maintain target tracks in a computer with periodic information updates from a scanning radar.
2. Get a search radar that can “help” solve fire control problems.
3. Sensor continues to perform primary function of search (scanning) and data input.
4. Computerization allows the system to perform a target tracking function.
5. Eliminates process of target designation from search radar to fire control radar.

6. Functions of TWS Detection Correlation
Track Initiation and file generation (if a new target)
Tracking “Gates”
Gate prediction, smoothing and positioning
Predict future target position
Computers make Track-while-scan possible. Scanning radar information is converted into binary (computer) information. All of the fundamental actions of a TWS system occur in the computer.
The computer:
1. Target Detection: Takes the scanning radar output, does analysis of the information and determines if the returns are from a target or just random noise.
2. Correlation: Determines if the target is a target previously detected or a new target. The computer does this by comparing the information received from the previous scans.
3. Track Initiation and File Generation: If it is a new target, the computer will start a file on that target. In the file it puts the position information on the target and will update the information with each subsequent scan.
- The computer can also add information on the target from other sensors and sources (including from other radars.)
4. Tracking Gates: Generates tracking gates (small volumes) around the target. With more information the gates get smaller.
5. Track gate prediction, smoothing and positioning: Same feedback and smoothing process used in previous discussions of conical and mono-pulse radars.
6. Future target position: Uses information to predict mathematically where the target will be. Eliminates the feedback problem of always lagging the target.
Designed to LEAD THE TARGET.

7. Gate Generation Acquisition gate Tracking gate Turning gate
* Gates are 3-dimensional pieces of space that
the target occupies.
* Size of Gates are determined by the computer
based on the information.

8. Acquisition Gate 10 degrees 10 degrees 2000 yards
Acquisition gate: Large volume of space, searching gate

9. Tracking Gate 1.5 degrees 1.5 degrees 120 yards
Tracking gate (smaller): Small well defined space

10. Turn Detection Gate *Computer determines size of gate tracking gate
3. Turning gate: Overlaps tracking gate, and varies in size depending on the speed and maneuverability of the target.

11. TWS Processing Original Course Turn Detection Gate Tracking Gates
1. Use the graphic to explain how gates work and the use of the three types of gates.
a. Acquisition Gate: Based only only on instantaneous position of target.
b. If next scan shows the target is still in acquisition gate:
- now have information to predict where the target will be next scan
- so can reduce the gate size to smaller tracking gates.
- Tracking gates can get smaller as get more (and better) track history.
c. If target is not in a tracking gate as predicted, he must have changed
course or slowed or both.
- Make a larger turning gate to try to pick up the target again.
- Once found subsequent tracking gates can be reduced in size.
2. Same process can be used for multiple targets.
3. When ready to fire can hand over target information (position, course, speed and range to the fire control system who locks on and fires then is ready for the next target.
4. Each contact is consider a new target unless determined to be consistent with a target held on the previous scan. (in turning gate).
5. If more than one target is in a gate or if two gates overlap the the computer has protocol to sort out the contacts. If they can’t be sorted out then they are considered new targets and files are created and they are tracked.
Acquisition
Gate

12. Track Initiation and Track File Generation
Store position and gate data
Code for acquisition window
Calculations on the return of a target are done by a computer.
Much too slow to maintain a small tracking gate.
Position History
Velocity History
Acceleration History
Window - acquisition code, position of gate center
- track code, position of gate center
All data is converted from polar to rectangular coordinates by the computer.
The data is used to perform various calculations necessary to maintain the track.
As the data is needed for computation or new data is to be stored, the portion of the memory allocated for the data will be accessed by the system software.
This method is much too slow to be used in a system where speed of operation is one of the primary goals.

13. Positioning and Smoothing Functions
Repositioning and smoothing must be done within the TWS algorithm.
“Lagging” Target
“Leading” Target
This is done mathematically.
Instead of the system “lagging” the target, the tracking gate is made to “lead” the target and smoothing is accomplished by comparing predicted parameters with observed parameters and making adjustments based upon errors derived from this comparison.

14. TWS Diagram Scanning radar detects a target Do parameters match
those from previous
scan NO
Yes
Does
track ambiguity
exist
Generate a
new track file
& store data
Generate an
acquisition
gate
Resolve
ambiguity
Target
previously in track
or acquisition
Compute
target tracking
parameters
Acquisition
Track
Generate
Track Gate &
indicator in file
Update
tracking
Reposition track
gate centered on
future position
Ready for the
next radar scan
information
Recompute
track gate
1. Track parameter storage, predicted track, gate determination, past history are all performed by computers which receive information from the scanning radar.
2. You can’t talk computers without a flow chart so here it is as a review.
Show slide. And explain what the tracking computers do.
- Show that this process can work for multiple contacts.

15. TWS Radar System Advantages
Scan and Track on same system
Tracking information used for computation of a fire control solution.
Immediate Fire Control Solution
Stress the following:
a. Search radar searches and identifies contacts (uses previous sweep’s information to determine if each return is that of a contact that is being tracked or is a new contact).
b. Only when going to use a weapons system is a fire control radar and launcher system assigned. The target’s position and track information
is then shared from the tracking computer.
c. This allows continuous track on targets but receives the fine tuning of the target of interest’s parameters to the Automatic tracking system of the angle-tracking servo, feedback enhanced for fire control radar.

16. Real World Applications
AN/SYS-2 IADT
used on some missile ships
Mk 92 CAS - FFG
AN/SPQ-9 – 5” Gun
Mk 23 TAS – NATO Sea Sparrow
AEGIS C&D
holds track files for AEGIS
dedicated computer
AN/ SYS-2 IADT - Integrated Automatic Detection and Tracking: used aboard missile ships. The system is used to develop a single track file based on the outputs of several files. Combines the best capabilities of all the sensors employed.

17. FFG 60 – USS Rodney M Davis

18. DD 982 – USS Nickelson

19. DDG 81 – USS W. S. Churchill

20. Summary Radar continues scanning Computer predicts positions
Track while Scan!
Track information used for fire control solution.

21. Questions?