2D vs 3D Sonar Processing
WARNING: Technical Jargon Ahead
FarSounder has approached sonar system design fundamentally different than other sonar technologies. The solution FarSounder's technology provides is the ability to deal with multi-path and water depth issues, allow for fast refreshes, and create a large field of view with single pings, all in a small cost effective package. FarSounder's approach does not hurt marine life and can be used as a marine mammal shipstrike mitigation device.
FarSounder's single ping, 3D sonar approach enables the system to overcome traditional Forward Looking Sonar limitations such as Multipath Interference, Shallow Water Operation, Roll/Pitch Compensation, Surface Effects and Ship Motion.
When used as a navigation device in shallow water, other 2D technologies often fall short of being effective navigation tools. These systems are very good at finding the range and bearing to a single target in deep water. However, by definition, there are targets at every range and bearing in shallow water. Those 2D systems cannot distinguish between the safe sea floor and the dangerous in-water obstacle through depth measurement. They must rely on visual cues to guess whether or not the obstacles are located in the water column or on the sea floor. The need for visual cues forces those 2D systems to have very high horizontal angular resolution. Unfortunately, this causes the systems to require many listening channels and requires a footprint for the receive array or lens aperture that is very long in terms of wavelengths. This long aperture requirement drives the systems to a higher frequency which in turn excludes them from long range capabilities.
To illustrate the difference between these two approaches consider the following figures.
In figure 1, real data of a pier wall bulkhead collected with a FarSounder 3D sonar system is processed as a simple 2D horizontal slice. In this display, color is mapped to signal strength where red is "loud" and blue is "quiet". The angular resolution is roughly equal to the existing off-the-shelf Forward Looking Sonars (FLS) -- also called Collision Avoidance Sonar Systems (CASS) or Obstacle Avoidance Sonars (OAS) -- manufactured by various companies. There is clearly a feature caused by the pier wall crossing the field of view at about 45° (noted with the dotted line). Yet there is also another feature or "bright" spot noted by the oval. As a navigation tool, this 2D display is not very effective.
In figure 2, this same ping has been processed with FarSounder's 3D processing using patented Target Model technology. In this image, color is mapped to depth. The view is a look down orthographic projection, yet targets are actually plotted in 3D space. Note the clear presence of the pier wall (shallow) in red and the sea floor (deep) in blue.
In figure 3, the same data is plotted in 3D space with a rotated perspective view. Note how clear it is to see the navigation hazards in 3D with this processing technique.
Without 3D capability, Forward Looking Sonars are unable to easily compensate for roll and pitch without large amounts of expensive hardware. Even in these cases, 2D roll and pitch compensation is marginal at best. FarSounder's technology is capable of compensating for roll and pitch entirely in software with a simple, inexpensive roll and pitch sensor.