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Overcoming the Nadir Gap with Mosaicked Sonar Data

Unmanned Undersea Vehicle (UUV) missions often involve the use of side scan sonar for wide area surveys. To create an image of the sea floor, side scan sonar produces narrow beams from the side of the sensor that scan large areas along the mission path. During the side scan survey, the region directly below the sensor, commonly refereed to the nadir region, is left unscanned. To overcome this gap in the data, UUV operators have historically planned missions with overlapping runs to capture the missing data. This caused increased overall mission run time and increased the risk for missing an important target.

 

L3 Technologies is overcoming the gap in side scan sonar data by integrating both side scan sonar and a forward looking sonar on its Iver4 UUV platform. The side scan sonar and forward looking sonar are run simultaneously while the Iver4 follows its mission plan. The two data sets are then mosaicked together using the SonarMosaic software to create one image that shows the complete scan area without a nadir region. By collecting both side scan and forward looking sonar data together, Iver4 operators will save significant time in data collection. It also significantly reduces the risk of missing a target that might have been hiding in the nadir region.

 

The data shown in this mission example was collected by an Iver UUV in San Diego Bay, CA. The Iver used for this mission was equipped with the EdgeTech 2205 side scan sonar and the Oculus 750d forward looking sonar. If only side scan sonar data was used (figure 1), there is a possibility that the shipwreck target location may have been missed in the nadir region of the scan. By mosaicking the forward looking sonar data (figure 2) with the side scan data, the Iver operator was able to locate a shipwreck target (figure 3) located in the bay channel with minimal passes run during the mission. This saved the operator time and ensured that the target was located.

Side Scan with Nadir Region
Figure 1- Side Scan Data with Nadir Region
Forward Looking Sonar
Figure 2 - Forward Looking Sonar Data
Mosaicked Sonar Data
Figure 3 - Side Scan Sonar Data Mosaicked with Forward Looking Sonar Data

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