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ROV Locator
  • ROV Locator
  • Overview
  • General Specifications Mk II
  • General Specifications Mk III
  • System Variants
  • Fundamentals Useful to System Designers
    • Sound Reflection and Absorption
    • Multipath
    • Ping Length
    • What to Do About Multipath and Other Issues
    • Clock Drift Expectations
    • Accuracy Expectations
      • Accuracy Test: Topside GPS
      • Accuracy Test: 110 Meter Slant Range
      • Accuracy Test: 295 Meter Slant Range
    • Operation in a Pool
  • Autosync Option (Mk II Only)
    • Autosync Mission Scenarios and Mission Suitability
    • Autosync Availability
    • Autosync GPS/GNSS Output
  • ROVL Channels (Autosync only; Operating Multiple Units in Proximity)
  • ROVL Coordinate Systems and Angles
    • Definitions
    • NED or “Compass” vs. ENU or “Math” Angles
    • Math to Compass Frame Conversions
    • Transducer Down Orientation
    • Transducer Up Orientation
    • Receiver/Transceiver Orientation Frames
    • Best Operating Envelope
  • Communicating With the ROVL
    • Serial Parameters
    • Packet Format
    • Messages from ROVL to Host
      • $USRTH Receiver-Transmitter Relative Angles Message
      • $USINF Information Message
      • $USERR Error Message
    • Messages from Host to ROVL
      • NMEA-Format Messages to Receiver
      • Valid Commands from Host to ROVL
  • Inertial Measurement Unit (IMU)
    • How To Tell Which IMU is Active
    • Mk II IMU Modes and Calibration
      • Mk II IMU Calibration Background
      • Mk II IMU Calibration General Procedures
    • CIMU Calibration Background
      • CIMU Magnetometer Calibration
      • CIMU Accelerometer Calibration
      • CIMU Gyro Calibration
  • Operating and Accuracy Considerations
  • Multi-Unit Operation (Swarms)
    • Multi-Unit 1:1
    • Multi-Unit 1:2
    • Multi-Unit 2x1:1
    • Multi-Unit n:1 (fixed transmitter)
    • Multi-Unit n:1 (mobile transmitter)
  • ROVL Mounting and Wiring
    • ROV/Deepside Mounting
    • Topside Mounting
    • Simple Topside Deployment Fixture
    • Wiring Notes
    • Electrical Noise
    • USB Interface using Blue Robotics BLUART Board
  • Mechanical Drawings
    • Mounting Footprint and Envelope, "S" Package
    • Mounting Footprint ("P" Package Mk II and Mk III)
    • Envelope Drawing. "P" Package ROVL Mk II Transmitter and Receiver, Mk III Transponder
  • Appendix: Math for Computing Remote Latitude/Longitude
    • Receiver & GPS at Topside and Transmitter Deepside
    • Transmitter & GPS Topside and Receiver Deepside
  • Appendix: Factory Usage Command Set
  • Troubleshooting
    • How to Tell if Your Mk II Receiver is Working
    • How to tell if your Mk II Transmitter is working
    • What to do when you find an unresolvable problem when troubleshooting
  • Copyright
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  1. Fundamentals Useful to System Designers

Multipath

A definition of multipath and some examples

PreviousSound Reflection and AbsorptionNextPing Length

Last updated 2 years ago

All sonar systems are affected by multipath, a phenomenon created by sonar signals following more than one path between a transmitter and receiver.

Multiple signal paths are created when a sonar signal reflects off one or more interfaces, and the reflected signal(s) combine with the direct-path signal causing constructive and destructive interference. The interference can create changes in the amplitude of the combined signal, and can also create changes in the phase of the received signal, when compared with the original signal. Additionally, the combined signal may appear to arrive from a direction different than the original ping, which will cause location errors.

Generally, the more specular the reflecting surface, the more potential to interfere with the original signal and thus the operation of the ROVL. The good news about Lambertian reflection is that the energy of the incident sound is reflected in all directions, which means the energy in any given outbound ray is much smaller than the incident energy, and thus the potential to interfere is smaller.

The figure below shows the ideal operating conditions for the ROVL. The transmitter and receiver are suspended in deep water free of obstacles such that no reflection can reach the receiver before the entire original ping has been received. Of course, this is essentially an impossible constraint, but the closer you can come to achieving it the better the ROVL will work.

Note that slant range is measured from the arrival of the leading edge of the signal, so even if multipath interference is present, the slant range is normally accurate.

Many types of multipath (red lines) are possible. The red lines show various undesired paths the signal can take to interfere with the operation of the ROVL system.
Ideal ROVL operating conditions are when all reflected paths (red, orange, blue) are longer than the the direct signal path (green) by at least the length of the signal "ping". This example ignores any reflections created by the ROV itself.