Navr4030 16(tides)

Lesson 16: AdvancedNavigation Systems

• AGENDA:– NAVSTAR Global Positioning System– Ship’s Inertial Navigation Systems (SINS)– Bottom Contour Navigation – LORAN-C– Electronic Charts (Raster & Vector)– Navigation Sensor System Interface (NAVSSI)

• Applicable reading: Hobbs pp. 540-572.

Lesson 20: Advanced Navigation Systems

NAVSTAR Global Positioning System (GPS)

• GPS = Global Positioning System– A space based, all-weather, jam resistant,

continuous operation, worldwide radio navigation system.

• Provides extremely accurate 3D location data as well as velocity and time.

• 3 LOPs provide a Lat. & Long.

• 4 LOPs provide Lat., Long. & Altitude

NAVSTAR GPS Specifications

• Frequency: 1227 MHz, 1575 MHz

• Range: Worldwide

• Accuracy: next slide

• 3 Types:– SPS- Standard Positioning Service– PPS-Precise Positioning Service– Differential GPS- for military only

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

NAVSTAR GPS Uses

Civilian Uses• Marine Navigation• Law Enforcement• Hydrographic

surveying• Search and Rescue• Collision avoidance

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

Vehicles (UAVs)

Differential GPS

• A receiving station located at a fixed, known location receives fix information from GPS.

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

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

Differential GPS

• GPS error information is then transmitted to vessels operating in the area.

• The resulting fix accuracy is 2-5 meters using the differential technique

• Requires more than 1 receiver

GPS

Advantages• Continuous Coverage

(regardless of weather)

• worldwide coverage

• 3-D locator

• Precise Timing Standard

Disadvantages• Vulnerable to Attack

Inertial Navigation Systems

• Inertial Navigation: the process of directing the movements of a vessel based on sensed accelerations in known spatial directions.

• System uses:– Gyroscopes– Accelerometers– Electronic computers

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

Inertial Navigation Systems

• Two types:– SINS (Ship’s Inertial Navigation System)

• first used in 1960s

• getting phased out

• must be reset periodically

– ESGN (Electrostatic Gyroscopic Navigation)• operates in a near perfect vacuum

• rotor is solely supported by an electrostatic field

• essentially frictionless

• resets only required once every 30 days

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.

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

LORAN (Long Range Navigation)

• Over the years, many ground based electronic navigation systems were developed prior to satellite based systems becoming possible.

• Most of these have been taken out of service, but LORAN still enjoys popularity and is still widely used.

LORAN (cont)

• The operating principles of the system are similar to those now used by GPS.

• Ground stations, at known locations, transmit signals at a predetermined time.

• These signals are received by vessels at sea, and the time delay is used to form a range LOP.

LORAN (cont)

• First established in 1957.

• Theory-hyperbolic LOPs based on time differences between master and secondary stations.

• Run by the Coast Guard

• Frequency: 100 kHz (LF)

• Range: 1200 nm

• Accuracy: 200-500 yds

Electronic Charts

• Electronic Chart Display Systems (ECDS)• Raster Chart Display Systems (RCDS)

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.

Homework

• Ch. 30– Section 1: 1– Section 2: 1, 5, 6, 9

• Ch. 31– #4c, 5, 6