Silicon Chip – June 2019

siliconchip.com.au Australia’s electronics magazine June 2019 15

Bet you’ve never heard of

beam sonar, using an array of transduc-

ers and powerful computers to form

3D images of the seabed or river bed

under a ship, or a towed sonar array.

But electronic/acoustic water depth

measurements go back over 100 years

and simpler methods have been in use

since antiquity.

Fig.1 shows a comparison of the

three most common modern sound-

ing techniques. We’ll now describe the

history of sounding techniques, start-

ing from the beginning and proceed-

ing to the present and the latest sonar

and LIDAR systems.

Historical bathymetry

Seabed mapping has been per-

formed since ancient times. It was

practised by the Ancient Egyptians,

who used poles and ropes, and also

the ancient Greeks and Romans, who

used a rope with a weight on the end

to determine depth, known as a lead

Fig.2: a lead line or sounding line

showing different markers at tradit-

ional depths of 2, 3, 5, 7, 10, 13, 15,

17 and 20 fathoms. A fathom is today

defined as exactly six feet or 1.8288m.

Fathoms and feet are still used on

US nautical charts whereas other

countries use metres.

Fig.1: three different sounding methods in use today. A lead line or sounding line, used since ancient times, gives

spot measurements; a single beam sonar is capable of giving continuous measurements although some still give spot

measurements; multibeam sonar can scan a wide area in one pass and can quickly build up a seabed map. Laser systems

such as LADS give similar results to multibeam sonar.

line or sounding line – see Fig.2.

Such lines were the primary meth-

od of determining seabed depth right

up until the 20th century, and are

still used today a backup to electronic

depth sounding systems (sonar).

In the 19th century, attempts were

made to automate the lead line sound-

ing process. These employed mecha-

nisms which would indicate when the

seabed had been reached.

Among these were Edward Massey’s

sounding machine, employed by the

Royal Navy, who purchased 1750 of

them in 1811. There was also Peter

Burt’s buoy and nipper device.

These devices were designed to

work up to around 150 fathoms’ depth

(275m). In the late 19th century, the

installation of undersea telegraph ca-

bles created a much greater demand

for depth measurement.

Lord Kelvin (then Sir William

Thomson) developed and patented