By: Thadd Barker and Scott Bowles

ES 351 - Intro to Geospatial Analysis

May 8th, 2014

Table of Contents

Line and Sinker Method

Thomson Sounding System

Acoustic Sounding System

Cold War Era

Technology Used Today

    Sounding is the action or process of taking measurements of the depth of the sea floor or any other body of water. These measurements are used in bathymetry, which is the study and mapping of seafloor topography. The topography of the sea floor was highly unknown in the early nineteenth century, due lack of technology and because there was no specific need to know the configuration of the sea floor. This changed during the 1840’s, with mankind's increased curiosity and the advent of Line and Sinker Sounding. Knowledge and details of the seafloor grew exponentially with the advancement of Acoustics Sounding System, following World War I.  The Acoustic Sounding Systems were capable of precise detailing of small features of the seafloor, while the Line and Sinker method could only discover large features.  Advancements in techniques of sounding systems are still taking place today allowing for even more precise and extensive mapping of the seafloor

Line and Sinker Method:

    First used by the U.S. Coast Survey and British explorers in the 1840's, a weighted rope would be dropped over the side of a ship and the length of line was recorded once the weight contacted the ocean floor. This simple method of measuring the seafloor was able to detect such features as the Mid-Atlantic Ridge, Mariana Trench, Challenger Deep, and Tuscarora Deep.

Thomson Sounding System:

    The Thomson Sounding System is similar to line and sinker sounding method. The main difference being that piano wire was used rather than hemp rope. Sir William Thomson, also known as Lord Kelvin, developed this method of sounding in the 1870’s. The use of the piano wire method made gathering depth measurements three times faster and an order of magnitude more accurate than the line and sinker system, mainly due to the small cross section of the wire was affected less by surface and subsurface currents. Variations of the Thomson Sounding System were made by the US Coast and Geodetic Survey and different British surveyors, which resulted in the Sigsbee Sounding Machine and Lucas Sounding Machine.  The Thomson Sounding System and its variations were used to discover such features as the continental shelves and slopes, mid-ocean ridges, enclosed basins, and major trenches.
Lord Kelvin
Figure 1. William Thomson
tanner sounding machine
Figure 2. Variation of Thomson Sounding System

Acoustic Sounding System:

    Acoustic transducers were developed in the 1912 by Reginald Fessenden of the Submarine Signal Company to both transmit and receive sound for the purpose of detecting objects in the water. Unexpected reflections of the seafloor resulted in acoustic sounding systems, also known as echo sounding. Echo Sounding determines bottom depth from measuring the time required for a sound pulse to be emitted from a transmitter, travel to the bottom and be reflected, and then travel back to a receiver unit. Dividing this time by 2 and multiplying time the velocity of sound in seas water gives the measure of the depth. Advancements of Fessenden’s transducer were made by German, French and American investigators.  Forward Looking Systems were developed using the transducer as an anti submarine warfare system. The first truly functional depth measuring device was created in 1922 and that same year the Hayes Sonic Depth Finder mounted on USS Stewart, a Navy Destroyer during World War I. The Hayes Sonic Depth Finder created a seafloor profile from Boston to Gibraltar, which proved its efficacy, ease of use, and accuracy. Between 1925 and 1927, the German Meteor Expedition used echo sounding and mapped the axis of the Mid Atlantic Ridge, as well as the abyssal hills extending outward from the ridge axis. Later in 1937, the United States Coast and Geodetic Survey mapped lineal chains of sea mounts and guyots in the Gulf of Alaska, large canyons off the east coast, and the Mendocino Escarpment off California.
Figure 3. Navy Destroyer equipped with Hayes Sonic Depth Finder

Cold War Era:

    In the late 1950's, The Deep Tow Vehicle (DTV) was developed by Scripps Institution of Oceanography to understand micro-topography as part of Defense requirement during the Cold War. The DTV is towed behind a research vessel along a predetermined path across the ocean to take measurements. The DTV has given scientists some of the most precise profiles of the ocean floor ever observed. This instrument became one of the most useful and precise research tools for studying the ocean floor as the arrow beam echo sounder, magnetometer, side scan sonar, bottom penetration sonar, photographic capability, and other sensors were added.
    In the early 1960's General Instruments Corporation for a "sonar group" consisting of engineers and scientists to develop an aerial radar mapping system. The final result was the Sonar Array Sounding System (SASS), which uses fan beam technology. This system records sixty-one individual depths for each emission of the sonar system, creating a highly detailed contour map of the ocean floor. Following the development of SASS, a commercial swath mapping system known as Sea Beam was developed and used by Australia, France, and the United States.
    With the invention of swath-mapping technology, the Lamont Geological Observatory, Woods Hole Oceanographic Institution, and Scripps Institution of Oceanography were able to map features that were previously hidden.  These intuitions were responsible for the discovering the abyssal plains, extensive fracture zones and their accompanying scars, surveying hundreds of sea-mounts and guyots, as well as mapping the full extent of the ocean ridge system. The Challenger II, of the United Kingdom was also established that the Mariana Trench is the deepest spot in the ocean.

Technology Used Today:

  • Satellite Altimetry uses satellites orbiting the Earth to measure subtle or permanent large scale features and differences in sea surface height.

  • Submarines have allowed the exploration of any specific location on the ocean floor, but they are not well suited for large scale exploration unless equipped with sonar.
Figure 4. (NOAA)
  • Unmanned Underwater Vehicles, like submarines, allow a certain area of the ocean floor to be explored, but depending upon visibility certain feature may not be visible. They are smaller and more maneuverable than submarines, as well safer due to the fact that no one has to manually control the vehicle from within.
AUV sitting on pier in foreground with BAY HYDROGRAPHER in the background tied up to pier.
Figure 5. (NOAA)
  • Multi-beam Sonar is used by oceanic vessels use multiple echo soundings to map narrow swaths of the ocean floor. Examples are shown below.
Figure 6. (NOAA)


  • Deep Tow Vehicles are pulled behind ocean going vessels and use highly precise instruments to map topographic features below the seafloor, as mentioned above. 

Figure 7. (NOAA)

NOAA Ship Fairweather

Figure 8. The Fairweather, owned by NOAA is designed and outfitted for conducting hydrographic surveys in support of nautical charting. (NOAA)


  • Theberge, Albert E. "NOAA History - Tools of the Trade/Surveying and Mapping/Sounding Pole to Sea Beam." NOAA History - Tools of the Trade/Surveying and Mapping/Sounding Pole to Sea Beam. N.p., n.d. Web. 08 May 2014

  • Dierssen, Heidi M. Theberge Jr. Albert E. Bathymetry: History of Seafloor Mapping. Encyclopedia of Natural Resources. 
  • "Underwater Vehicles." / Underwater Exploration / Ocean Floor / Science Topics / Learning / Home. N.p., n.d. Web. 08 May 2014.