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?