Observation range versus operational frequency

Absorption increases dramatically with frequency in salt water. For maximum observation range you should select a low operating frequency, a large transducer and the maximum transmit power.

The key facts related to observation range versus operational frequncy are:

•

Observation range increases when the operational frequency is reduced.

•

Resolution increases when the operational frequency is increased.

If you wish to work in deep waters, you need a low operational frequency.

If you wish to work with high resolution, you need a high operational frequency. The observation range is then limited.

Using the Simrad ES38B transducer (38 kHz, 7x7 degrees, 2000 W) you can observe a 60 centimeter cod down to 950 meters, while bottom detection works down to 2800 meters. However, with the Simrad ES200-7C transducer (200 kHz, 7x7 degrees, 1000 W) you can only observe that same cod down to 270 meters. Bottom detection becomes unreliable below 500 meters.

Typical observation ranges are shown in the table.

Maximum detection depth (Split-beam transducers)
Transducers	Frequency (kHz)	Pulse duration (ms)	Bandwidth (hz)	Tx Power (W)	Range fish (m)	Range bottom (m)
ES18-11	18	8,21	382	2000	1100	7000
ES38B	38	4,09	766	2000	950	2800
ES70-11	70	2,05	1526	800	450	1100
ES120-7C	120	1,02	3026	1000	440	850
ES200-7C	200	1,02	3088	1000	270	550

Maximum detection depth (Single-beam transducers)
Transducers	Frequency (kHz)	Pulse duration (ms)	Beam angle (deg)	Bandwidth (Hz)	Tx Power (W)	Range (m)
38-7	38	4	7	766	2000	3000
38-9	38	4	9	766	1500	2600
38/200D	38	4	13x21	766	1000	2100
50/200D	50	2	10x16	1493	1000	1400
50-18	50	2	18	1526	500	1400
50-7	50	2	7	1493	2000	1900
120-15	120	1	10	3026	1000	800
200-7	200	1	7	3088	1000	500
710-36	710	1	2,8	3088	100	70
38/200	200	1	7	3026	1000	450
50/200	200	1	7	3088	1000	450

These range calculations assume a normal sea water salinity (3.5%) and temperature (+10°C), an average bottom (surface backscattering strength = -20 dB) and a noise level typical for a moving vessel.