Lesson 14: AdvancedNavigation Systems

• AGENDA:– NAVSTAR Global Positioning System (GPS)– Inertial Navigation Systems (INS)– Bottom Contour Navigation – Electronic Charts (Raster & Vector)– Navigation Sensor System Interface (NAVSSI)

• Applicable reading: Hobbs pp. 540-555.

Lesson 20: Advanced Navigation Systems

NAVSTAR Global Positioning System (GPS)

• GPS = Global Positioning System– all-weather, jam resistant, continuous operation, real-

time, passive, worldwide radio navigation system.

• Provides:– Extremely accurate 3D position data– Extremely accurate velocity data– Precise timing services– 3 LOPs provide a Lat. & Long– 4 LOPs provide Lat., Long. & Altitude

NAVSTAR GPS Uses

Civilian Uses• Marine Navigation• Law Enforcement• Hydrographic

surveying• Search and Rescue• Collision avoidance

Military Uses• Rendezvous• Close Air Support• Mine Warfare• Unmanned Aerial

Vehicles (UAV/s)

WRN-6

WRN-6

Differential GPS (DGPS)

• A receiving station located at a fixed, known location receives position data from several GPS satellites.

• The data obtained from GPS is compared to the known location of the station.

• Any difference between these two is due to GPS error.

• This difference the applied to the individual GPS receiver and thus, increased positional accuracy is obtained

NAVSTAR GPS Accuracy

Standard Position Service (SPS)

• Position: 100 m Hor. 150 m Vert.

• Velocity: .5 m/sec

• Time:1 milli-second

Precise Position Service (PPS) - Military

• Position: 16 m Hor. 25 m Vert.

• Velocity: .1 m/sec• Time:100 nano-

seconds

Inertial Navigation System (INS)

• Inertial Navigation: the process of measuring the movements of a vessel based on sensed accelerations in known spatial directions. – Gyroscopes– Accelerometers– Electronic computers

Inertial Navigation Systems (cont)

• Integrating acceleration gives you velocity• Integrating velocity gives you position/distance

traveled• Need to compare to fix, since output is an EP!• Can go up to 30 days w/out update, in theory

– Typically go no longer than 7-14 days

• Types– SINS– ESGN– RLGN

Inertial Navigation Systems

Current position is inputted

Spinning gyro

Accelerometer

Computer

Xo

F=m*a

Through Differentiation we get velocity and position (V and Xf)

Known mass

Bottom Contour Navigation

• Establishes position by using the geographic features of the ocean floor.

• An echo sounder (fathometer) is used to produce a trace of the ocean floor beneath the vessel, which can be compared to a bottom contour chart to establish the ship’s position.

• Can be used as a fix source, but is only accurate when large ocean floor gradients exist

Bottom Contour Navigation

• 2 Techniques:

– Line-of-Soundings (page 567 in Hobbs)

– Contour Advancement (page 568 in Hobbs)

Bottom Contour Navigation

Advantages• no satelites required• subs=> no need to go

to Periscope Depth (PD)

• not vulnerable

Disadvantages• not very accurate• requires a

cooperative sea bottom

Electronic Charts

• Raster Chart Display Systems (RCDS)• Electronic Chart Display Systems (ECDS)• Not approved for Fleet use, but getting closer

Navigation Sensor System Interface (NAVSSI)

• Provides/Distributes NAV data (precise position, time, velocity, pitch-roll-yaw) to multiple users.

• NAVSSI has been successfully installed, interfaced, and tested with WSN-5, WRN-6, EM Log, Tomahawk, Outboard, and NTCS-A.

• A similar system may be integrated into your ship’s Combat Control System (CCS)

Summary/Review

• How does GPS work?

• What is ephemeris and almanac data?

• Name 3 uses of GPS.

• How does differential GPS work?

• How do Inertial Navigation Systems work?