Single beam echosounders are by far the most numerous sonar systems in use today.  They are used on a wide range of vehicles from small pleasure boats, to huge cruise ships and tankers.  They span a wide range of applications including:

• Water depth indicators, both for bottom avoidance and for navigation
• Fish finding, both sport and commercial
• Bottom classification, (rock, silt, eelgrass, etc.)
• Military, target localization
• Upward looking, for submarine Ice avoidance
• Surveying, both for navigational charts and for resources exploration

While single beam echosounders are still widely used for surveying, the multibeam sonars are rapidly taking over this application because they are much more cost effective and have better horizontal and depth resolution than single beam sonars.

 SIngle beam sonars measure the time it takes for an acoustic pulse to travel from the sonar transducer to the sea bottom and back up to the sonar transducer.  The depth is given by the following equation.

Z=t*c/2

Where Z is the depth, t is the time, c is the average sound speed and  the division by two accounts for the pulse having to travel the distance in both directions.

The sources of error in the equation above are errors in time measurement and average speed of sound measurement.  In addition, for accurate positioning of the bottom knowledge of the sonar transducer's position is required (lat., Long. and elevation).  Errors due to to orientation (pitch and roll) are not usually a concern since echosounders use a wide beamangle to compensate. 

Positioning accuracy can be addressed with accurate GPS technology.  Each ping of the echosounder can be stamped with a position from the GPS.  Phase measuring GPS systems can measure to within 0.1m in three dimensions.

Modern echosounders have very accurate timing and triggering circuits.  Depth errors due to timing in the echosounder are typically sub mm, so this is not a concern.

The average sound speed measurement however is more difficult to obtain accurately.  This then is the primary source of error for echosounders.  The speed of sound in surface water can vary from 1400 to 1550 m/s, a 10% variation.  For an echosounder to acheive an accuracy of 30cm in 100m of water the average sound speed must be known to within 0.3%.

Since the sound speed in water varies with temperature, salinity and pressure the sound speed can vary dramatically based on location.  It can also vary dramatically from the surface to the sea floor as a result of thermal and salinity stratification of the water.  To accurately determine the average sound speed from the transducer to the seafloor it is necessary to send an instrument down to to measure it.

All of the direct measuring sound speed profilers and CTD profilers being manufactured today can meet the single beam echosounder accuracy requirements.  What differentiates sound speed profilers for this application is ease of use.

 There are several ease of use factors to consider:

• Profiling speed.  The less time spent doing sound speed profiles the more time can be spent surveying.  Typically direct measuring sound speed profilers can profile faster than CTD based profilers.  CTD based profilers need to profile slower to reduce 'Salinity Spiking' errors.
• Automated averaging.  Some profiling system will automatically calculate the average sound velocity from the profile.  This saves the user time.
• Internal data logging versus cable.  For deep profiles a profiler with internal logging is a must.  For shallow work a cabled profiler allows the user to see the results in real time.
• User interface.