Navigation and Positioning Systems

Navigation and Positioning

• Position fixing: Measurement of distance and/or direction to known objects using identifiable external information (signals: GNSS, features: rivers, terrain height, buildings, etc.)
• Dead reckoning: Approximation of the location of an object using direction/course and distance traveled, with errors increasing over time

Integrated Navigation System

• Combines several navigation methods to provide accurate and reliable information
• Provides information about the accuracy and reliability of the navigation methods ("integrity")

Inertial Navigation System (INS)

• Uses accelerometers and gyros to measure the acceleration and orientation of the vehicle
• Calculates the position, velocity, and attitude of the vehicle based on the measurements
• Requires initial position, velocity, and attitude to be set

Integrated Navigation Solution

• Combines the INS with other navigation methods (e.g. USBL, DVL) to provide a more accurate and reliable position solution
• Uses an estimation algorithm to correct the position solution based on the measurements

Underwater Positioning

• The most obvious challenge with underwater navigation is that a continuously updated position fix must be estimated without a robust and dependable satellite reference (GNSS)
• Accuracy depends on the distance between the transceivers and the mounting method

Short Baseline (SBL)

• Advantages:
  • Only one transponder on the vehicle
  • Easy to use and ship-based – no need to deploy transponders on the seafloor
  • Good range accuracy
• Disadvantages:
  • Three or more transceivers on the ship are required
  • Error based on range and water depth (SVP required)
  • Accuracy dependent on the vessel's motion reference units

Long Baseline (LBL)

• An array of baseline transponders is moored on the seafloor at fixed locations and used as reference points
• Position determination by triangulation (distance measurements between the vehicle and each transponder of the baseline array)
• Advantages:
  • Highest possible accuracy (theoretical)
  • High position accuracy (depth independent)
  • Wide area of coverage
• Disadvantages:
  • Complex system requiring expert operators
  • Several transponders necessary
  • On-site installation time/costs
  • Calibration of baseline transponders necessary

Calibration

• Relative calibration: Determination of the shape and size of the LBL array, no absolute positioning in real-world coordinates
• Absolute calibration: Requires first a relative calibration, then the array is placed into real-world coordinates with one of many methods (e.g. Box-in, Block shifting)

GPS Intelligent Buoys (GIB)

• GIB systems are inverted LBL devices
• An array of baseline transponders is replaced by floating buoys, self-positioned by GPS
• Position determination by triangulation (distance measurements between the vehicle and each buoy)