Pulse duration concept
The pulse duration is controlled by the Pulse Duration parameter. In shallow waters a short pulse duration is used and in deeper waters a longer pulse duration is more useful.
The pulse duration is controlled by the Pulse Duration parameter. The minimum allowable pulse duration is calculated from:
Bfc = 3.63/PD + 0.87 BLFM
where:
•  BLFM = Bandwidth of Linear FM sweep
•  PD = Pulse duration in seconds
•  Bfc = 3.63/PD for CW pulse
Bfc is the bandwidth covered by the Fourier coefficients used in the beamforming. This number of Fourier coefficients is matched to give maximum ping rate, while providing a sidelobe level in range (time) at about -35 dB. In beam modes with less than -35 dB sidelobe level in space, is will be desirable to lower the sidelobe level in range as well. This is obtained by setting the Fc Factor larger than 1. When pulse duration is set, the value is automatically limited by the minimum allowable value. The decimation of element data samples to beam data samples is depending on the selected pulse duration. The decimation factor follow the below equation:
DF = 2 ^ Integer part ( Log 2 ((PD[s] * 62500) / (3.63 * Fc Factor) ) )
where:
•  DF = Decimation factor
Using this equation the decimation factor will be:
Pulse Duration [s] Decimation Factor
0.000064 - 0.000112 1
0.000128 - 0.000224 2
0.000240 - 0.000464 4
0.000480 - 0.000928 8
0.000944 - 0.001856 16
0.001872 - 0.003712 32
0.003728 - 64
The step size when changing the pulse duration depends on the pulse duration interval you started from. The step will always be 0.000016s times the decimation factor.
When you click Apply and recalculate the beam mode, the step size will be recalculated according to the selected pulse duration. In this way you can fine adjust your pulse duration selection by scrolling the pulse duration to the desired area. Repeat this process as many times as required. The 0.000064s pulse duration is obtainable for a beam configuration consisting of a single reference beam, using the entire frequency band and running in linear frequency/beam spacing.