Object Detection Using NORBIT Multibeam Sonar
In this case study we highlight the benefits of using different approaches for imaging underwater targets.
The applications for these techniques support:
- Search and Recovery Operations
- Environmental/Biological/Ecological Assessment
- Navigational Support for vessels in shallow water
Detecting detailed objects underwater
Detecting objects underwater using multibeam echosounders presents a variety of challenges.
Typical digital terrain models made from bathymetry data incur a loss of resolution as a function of grid size which makes detailed object representation more difficult. Also, operational considerations include conflicting needs such as “real time” operator aided inspection vs. offline post processed inspection of data.
NORBIT Survey: iWBMS and FLS Setup
For this case study we chose a novel dual head sonar configuration consisting of a standard NORBIT FLS imaging sonar mounted with a NORBIT iWBMS mapping kit.Both sonar heads were connected to a single SIU topside and run from NORBIT GUI software (v10.4.X) simultaneously.
The surveys were conducted from a RHIB vessel using a custom mounting arrangement made from inexpensive materials. RTK was provided via cellular network.
Results
Point Cloud vs. DTM
In this example we highlight the difference between a DTM and a Point Cloud representation of small and medium sized complex objects.
Anchor
Full resolution point clouds typically preserve the complex structure of small objects as shown below:
Environmental Assessment: Industrial drums (contents unknown)
These storage drums were located near a popular fishing location. Full
resolution point cloud data allows divers to have the maximum level of detail required to plan and support safe inspection and recovery.
Drums were detected in the riverbed using the Forward Looking Sonar (FLS).
Forward Looking SONAR (FLS) images also provide a unique representation of objects ahead of the vessel.
Lost containers, unknown contents
Lost shipping containers present a unique challenge for recovery. This container was inspected as a potential store for WWII ammunition. Understanding the structure's detailed orientation, how it lies, and the distribution of debris surrounding it is critical for safe recovery efforts.
Small sunken boat
Shipwrecks are a classic target for representing underwater structure and detailed objects.In this example we see a small fishing boat imaged using both mapping and imaging sonar modes.
Mannequin Imaging
Search and recovery in maritime operations includes the location and identification of human forms.In this example we experiment with detection of human forms in the mapping data.
Fish and Fish “dimples”
In this example, we see shallow structures created by fish burrowing into the sediment of a lakebed. This behavior creates “dimples” which are easily detected using FLS or iWBMS modes. Analysis of these structures could help assess population density and activity.
Shallow Water Navigation
In this example an FLS is used to maneuver around complex underwater structures in very shallow water (1-2m max). By Combining Google images with real time FLS an operator can easily navigate a reasonable path through a dense obstacle field. This example shows boat launch ramps from a decommissioned shipyard which is sometimes used for illegal dumping of waste and is located near residential fishing areas.
Fusing Imagery – FLS and Satellite Images
