Single target pulse properties

Single target pulse properties are output when an export of single targets from a region or a selection is performed from a single target echogram.

The following table details when each pulse property is applicable and available from the different types of single target echograms supported in Echoview.

See: Single target analysis variables for definitions of the variables.

Pulse property

single target detection - single beam

single target detection - split beam

single target detection - dual beam

Simrad single target E telegrams

HTI .RAW single target echograms

Precision Acoustic Systems .ts4 single target echograms

 PulseLengthDeterminationLevel

Y

Y

Y

Always 6dB

N

N

 Samples_above_PLDL

Y

Y

Y

N

N

N

 StandDev_angles_minor_axis

N

Y

N

N

N

N

 StandDev_angles_major_axis

 PulseLength_Normalized_6dB

Y

Y

Y

N

Y

Y

 PulseLength_Normalized_12dB

Y

Y

Y

N

Y

N

 PulseLength_Normalized_18dB

Y

Y

Y

N

Y

N

 PulseLength_Normalized_PLDL

Y

Y

Y

N

N

N

 Pulse_Start_Normalized_6dB

Y

Y

Y

N

N

N

 Pulse_Start_Normalized_12dB

 Pulse_Start_Normalized_18dB

 Pulse_Start_Normalized_PLDL

When pulse properties are not applicable or available the "no data" value of -9.90E+37 is output.

Pulse properties defined

The diagrams below describe the pulse properties.

Pulse Length Determination Level

Pulse Length and Pulse Start

Normalized pulse length

Single target pulse properties in Echoview are normalized to c*τ/2.

Where:

τ = transmitted pulse duration (s)
c = speed of sound (m/s)

The following is the justification for dividing by the factor of 2:

A transmitted pulse leaves the transducer, reflects from an object in the water column and travels back to the transducer. The transmitted pulse duration and speed of sound are known and the TimeOfReceivedEcho (at the transducer) is measured.

The distance in the water column that a transmitted pulse travels to an object is c * TimeToObject.

The distance in the water column that an echo travels from the object to the transducer is c* TimeFromObject.

Echosounders measure the time of a received echo, which is a round-trip time i.e. TimeOfReceivedEcho = TimeToObject + TimeFromObject. An echogram (range mode) or ping graph displays ping sample data at the calculated distance from the transducer.

The range from the transducer to an object is calculated using the TimeOfReceivedEcho and the speed of sound.

RangeOfObject = c* TimeOfReceivedEcho/2

As a result. given a transmitted pulse with a duration of τ in time, the pulse occupies a distance of c*τ in the water column and its range is c* τ/2.

Note: Normalized pulse length can be used to filter detected single targets. The filtering can exclude false single targets and remove spike noise.

Example of a single target pulse

Single beam method and pulse split beam method and pulse

See also

About Single target detection
Single target detection algorithms