ECE 5320 Mechatronics
Assignment #01: Literature Survey on Sensor and Actuators
Topic:
SONAR (SOund NAvigation and Ranging)
Prepared By:
Lee Gardner
Department of Electrical and Computer Engineering
Utah State University
Outline
– Reference list
– To probe further
– Major applications
– Basic working principle illustrated
– A typical sample configuration in application
(application notes)
– Major specifications
– Limitations
– And many more relevant issues in applications
(such as, how to choose, cost information, where
to buy etc.)
Reference List
• Mechatronics Handbook
• HowStuffWorks.com
• Sonar Made Simple, Ridgesoft LLC 2003
www.ridgesoft.com/articles/sonar/SonarMadeSimple.
pdf
• Sonar Theory and Application, Imagenex Model
85 Color Imaging Sonar User’s Manual.
http://www.imagenex.com/sonar_theory.pdf
Major Applications
• Object distance measurement.
• Object proximity detection
• Vehicle motion coordination and movement/location
mapping
• Detection, Classification, Localization, Identification
– Passive: just listen
• biological monitoring
– Active: transmit and listen (echolocation)
• surveying (side-scan), depth sounding, imaging,
fisheries
Major Applications Cont…
Active Sonar: Passive Sonar:
Benefits Benefits
Control of signal band. Minimal power
Direct access to range and requirement.
azimuth. Minimal impact on marine
Matched filter gain. mammals.
Drawbacks Clandestine surveillance.
Two-way transmission loss Drawbacks
Large power requirement. No range information.
Negative impact on marine Mini-submersibles and
mammals. divers are very quiet with
Source position and respect to ambient.
intention visible to all. No matched filter gain.
Basic Working Principle
• Sonar works by transmitting a wave (sound wave)
and listening for the echo of the sound.
• The received wave is measured and analyzed for
changes in amplitude and phase.
• The delay in the return of the “ping” and the
speed of sound can be used to determine the
distance of the closest object detected.
Basic Working Principle Cont…
Basic Working Principle Cont…
• The distance to the nearest object can be calculated by
dividing the elapsed time
Distance = Elapsed_Time/(2 * Speed of Sound)
• The factor of 2 comes from the fact that the wave
traversed the distance from sensor to object twice.
• Speed of Sound varies and is dependant on:
– Temperature
– Salinity
– Depth/Elevation
Transmission Loss (TL)
• Describes the “weakening” of the intensity of
sound due to a source at some point in the
transmission medium
• Affected by:
– Spreading
– Propagation details
– Absorption
– Forward reflection losses (boundaries)
• TL = 10log10(I0/I1) dB (here I0 is SL)
Working Model
• In many cases the sonar image of a target will closely
resemble an optical image of the same object.
Working Model Cont…
Imaging Sonar
Imaging Sonar
• Fan shaped beam
• Scans surfaces at shallow angles, usually
through a horizontal angle
• Displays color images or pictures
• Complete echo strength information for each
point
• Primarily for visual interpretation
Imaging Sonar Cont…
Characteristics necessary for visual image
• The angle through which the beam is moved
is small
• The fan-shaped beam has a narrow angle
• The transmitted pulse is short
• The echo return information is accurately
treated
Working Model Cont…
Profiling Sonar
Profiling Sonar
• Narrow pencil shaped beams
• Scans surfaces at a steep angle usually on a vertical
plane
• Displays individual points or lines
• Accurately cross-sections a surface
• Echo strength for each point higher than a set threshold
• Digitizes a data set for interfacing with external devices
• Data set is small enough to be manipulated in a small
computer
• Primarily a measurement tool
Working Model Cont…
Sonar Image Interpretation
• Image of a target will closely resemble an optical
image of the same object.
• A sonar image will always have less resolution than
an optical image.
• Rough objects reflect sound well in many directions
and are therefore good sonar targets.
• Smooth plane surfaces, may be difficult to see with a
sonar.
Image Interpretation Cont…
• It is often useful to scan targets from different
positions.
• An unrecognizable target from one direction may
be quite easy to identify from another.
• Usually the relative elevations of the targets are
not known, only the range from the transducer.
• Two targets displayed in the same location on the
screen may be at different elevations.
Image Interpretation Cont…
Image Interpretation
• You might see a target on the bottom, and a target
floating on the surface in the same place.
• By analyzing the shadows you can estimate the
height of objects above the bottom.
• Reverberation (clutter) is interference in an active
sonar return due to scattering from non-targets
– Interfaces
• Bottom roughness, bottom “features,” sediment
volume inhomogeneities
• Surface roughness, bubbles
– Volume (fish)
Major Specifications
• Range: The longest distance detectable from an
object.
• Sensitivity: Ability to detect subtle changes in
detected object
• Bandwidth: The range to detect motion and
movement in the object by measuring Doppler shift.
• Accuracy: The difference in the detected range to the
actual range.
Major Specifications Cont…
• Precision: Ability for the sensor to repeat results
given a particular accuracy.
• To avoid interference, sonar arrays must be fired
sequentially
• Noise susceptibility and filtering.
• Coverage area
Limitations
• Generally only used for under water applications
• Noise susceptibility can skew results
• High precision and accuracy sonar equipment are too
expensive for consumer use.
• Some objects are “invisible” to sonar and difficult to
detect.
• Precise image reconstruction is difficult do to very low
resolution echo’s
Cost
• Cost varies widely on use and application.
• Generic sonar systems can be made cheaply.
• High accuracy and specialized sonar systems can
be very expense. Usually only used by military
and industry.
• Precision Budget can grow extremely high for
high-end systems.
Where to Buy
• Many retailers (digikey etc…) have sonar sensors
available for consumer purchase.
• Specialized and high end sensors available through
industry channels.
• http://www.mstarlabs.com/adwds/adsonr01.html
• http://www.wg-
plc.com/international/security/underwater_surveillance_sy
stem.html