# A Wide-Area Deep Ocean Floor Mapping System: Design and Sea Tests
## 6 Discussion: Overall System Design and Performance  
In Section 3, we validated our ocean mapping system using a proof-of-principle sonar test in a scaled tank. The tank testing showed that the sparse-aperture concept is viable  
Figure 16: Initial sea testing of custom ASVs and sensors. Precision optical and LiDAR tracking of the vessel from shore (**a**) and boat (**b**). Figure 15: The in-lab test setup for precision-relative navigation is shown in (**a**). Example data frames from a near-infrared camera and LiDAR are shown in (**b**). Edge distances and interior angles calculated for tracking the ASV are shown in (**c**). despite the challenges posed by the tank size causing significant signal interference and multipath effects. We also showcased the application of our imaging algorithms and showed the convergence of reconstructed images as we varied resolution. We compared the reconstructed images from the three scattering models and concluded that the [PERSON] and [PERSON] bistatic model provided the best results. After demonstrating that the sparse-aperture concept is viable, in Section 4 we showcased the application of our system in reconstructing a 3D image of a sunken barge near Boston Harbor. We discussed details of our signal-processing and calibration chain and compared the image we obtained of the barge to that obtained by a commercial side-scan sonar. It should be noted that the imagery from our array was created using an initial algorithm set based on the signal-processing chain we developed for our tank experiment. Many aspects of the signal-processing suite would improve the quality of the imagery. Some of the possible improvements we are currently working on are listed in Table 1. In Appendix A, we discuss environmental impacts and how they can be expected to be limited compared to other systems. A sparse array design introduces higher sidelobes than a fully populated dense array of equal size. A high sidelobe allows acoustic energy from other directions to smear into the look location of the array and degrades the image quality. In Appendix B, we showcase such sidelobe effects and outline our algorithm to reduce them. Specifically, Figures 15 and 16 first confirm that a long inter-array distance introduces high sidelobe artifacts. Figure 17 shows that these sidelobe artifacts intensify for a spotlight-shaped transmit beam. This wide transmit beam illuminates a broader 2D patch of the seafloor than a 1D seafloor strip illumination from a narrow fan-shaped transmit beam and introduces more sidelobe energy leakage. We have developed a coherent sidelobe-reduction algorithm based on alternative projection [14] and the CLEAN algorithm of [PERSON] [29]. Our algorithm effectively reduces sidelobe artifacts for a modeled Lambertian seafloor example, as shown in Figure 18. This algorithm is currently under further development, and we are planning performance analyses on both simulated scenarios and real measurements. On the basis of our current ASV design, tracking system, and acoustic imaging, we have estimated the performance and costs of a fully operational array. Desired resolution of the seabed imagery determines the sonar operating frequency and the number and quality of navigation sensors needed to achieve the one-tenth-wavelength relative positioning accuracy. The accuracy requirement can be relaxed to one-third-wavelength with an autofocus mapping capability. A conventional deep-water multibeam sonar has about 1\({}^{\circ}\) beam and costs around USD 2 million. The sparse array technique will require long-endurance ASVs that cost about USD 75,000 each. At 1 m resolution, using our current GNSS-visual-inertial navigation setup will require installing a precision GNSS receiver capable of real-time kinematics (RTK), inertial measurement unit, and multiple cameras and LiDARs on vehicles. The total cost of the system will be USD 7 million At lesser resolution requirements, such as 10 m, fewer ASVs are needed, and each vehicle can be outfitted with a less exquisite navigation sensor suite.