beam characteristics and the frequency separation into account, NDS SCOUT reaches a 2D beam resolution of about 3 degrees times 3 degrees. This new technology opens the door to high-pre- cision direction of arrival finding for all detected objects. Other advantages are apparent when comparing the NDS SCOUT system with other possible array configura- tions, including a 2D receive array. A beam resolution as high as that provid- ed by the NDS SCOUT approach would require the installation of a planar array with a considerably higher number of channels. Such architecture would be more complex due to the expanded array and higher processing load. Ad- ditionally, it would need more integra- tion space. A 2D array complexity can be reduced by sparse array techniques, but at the cost of increased side lobe levels, which result in increased false- alarm rates.
As an alternative, NDS SCOUT uses horizontal beamforming and vertical frequency separation to ensure higher performance, greater affordability and a smaller footprint. Based on the 2D beam data, obstacle detection is per- formed, and the results are displayed on the HMI.
If an object is moving in the direction of the submarine, an alert is set to warn the operator. In addition to the per-ping detections, a Kalman filter is applied to track up to eight objects. The tracking results present a noise-reduced mea- surement of the object's position and a prediction of its movement. Results of this automatic tracking are also dis- played on the HMI. The multiple-frequency approach
ensures vertical and horizontal resolu- tion, which are standard with the NDS SCOUT system. Three-dimensional positioning is possible without further pings or an expensive combination of a planar array with 2D beamforming.
The BM mode uses the same elec- tronics as the OA mode. Only one of the transmit frequencies from the OA mode is used in the BM mode. The transmit pulse is emitted at an angle tilted steeper downward than the lowest transmit planes in OA mode. By tilting the transmit pulse in BM mode more than in OA mode, the back- scatter characteristics of the seafloor are optimized. The advantage to tilting
24 st / NOVEMBER 2012 www.sea-technology.com