# Smart Ocean: A New Fast Deconvolved Beamforming Algorithm for Multibeam Sonar
## 3 Experimental Results
### Real Data Experiment  
#### 3.3.1 Experimental Data Results of the Multibeam Sonar System  
In this section, we utilize the data from outfield experiments to analyze the performance of CBF and deconvolved beamforming. The equipment used in the experiment was a shallow water multibeam sonar system developed by the research group where the authors work, the number of array elements was M = 100, the array element spacing was \(d=\frac{\lambda}{2}\), the signal frequency was 200 kHz, CW pulse, and a pulse width 0.5 ms. The experimental site was an open shallow sea area with flat topographic topography, the level of sea condition was less than four, and the hydrologic condition was good.  
Figure 8 shows a single channel waveform in the time domain, which was compensated by TVG. The raw data was processed according to the procedure shown in Figure 6, and then we obtained the processed results of CBF and deconvolved beamforming, and we abstracted the beam power at the time 0.0933 s. As shown in Figure 9e, there are two main lobes, and this is because the experimental terrain was relatively flat, which led to the emergence of two strong echo points on the time slice. The main lobe width of deconvolved beamforming was narrower than that of CBF, and the noise level of deconvolved beamforming was about 5 dB lower than that of CBF, which is consistent with the simulated case above.  
Figure 9a shows the 2D image obtained by utilizing CBF. It is a convex arc and it can be roughly conjectured that the actual terrain is a relatively flat terrain. The beam (that is, the vertical incident and received) located in the top of the arc has the strongest main lobe and its side lobe leakage is obvious, which is called the tunnel effect [16]. Figure 9b is the enlarged result of the middle and upper part of Figure 9a, and more details of the side lobe leakage can be seen. If the strength of the side lobe is higher than the real echo of the same beam, which usually exists in the beam of small grazing angle, the estimate of the time of arrival (TOA) is wrongly regarded as being where the side lobe is using the  
Figure 7: (**a**) The 2D images utilizing CBF with the simulated flat seabed echo data, (**b**) utilizing deconvolved beamforming.  
energy center method [17]. Figure 9f shows this case, where the sinusoidal value (sin \(\theta\)) of the beam angle is \(-0.906\), and the strength of the real echo of CBF (solid line) is obviously weaker than that of the side lobe generated by the beam of the arc's top. There will be a mistake if the energy center method is used to estimate TOA under these circumstances. For deconvolved beamforming (dotted line), the strength of the real echo is still stronger than that of the side lobe generated by the beam of the arc's top, and the estimate of the TOA is still correct utilizing the energy center method. Figure 9c shows the 2D image obtained utilizing CBF, and the outline is the same as Figure 9a, but it is finer and clearer. The side lobe generated by the beam of the arc's top is significantly reduced and it is obvious that the tunnel effect is suppressed. Figure 9d is the enlarged result of the middle and upper part of Figure 9c.  
Figure 8: A single channel waveform in time domain.  
Figure 9: _Cont._