Validation of the propagation, target echo and sonar performance model ALMOST with near field target echo measurements

Validation of the propagation, target echo and sonar performance model ALMOST with near field target echo measurements

Schippers, P.
TNO Defensie en Veiligheid

Papadakis, J.S. (editor)
Bjorno, L. (editor)

2005

Since the late eighties the sonar performance model ALMOST of TNO Defence, Security and Safety is under development. For active detection performance first a point target with one Target Strength (TS) value dependent on aspect angle was used, based on measurements or other sources. Within the Torpedo Defence System Test Bed (TDSTB), developed at TNO, with ALMOST as the acoustic kernel, there is a demand for target echo (TS) modelling for ships, wakes, and mine-like targets. Therefore modelling of extended (nonpoint) targets was investigated. The method is based on coherent scattering from a 3-D surface constituted from dense pixels representing the specific size and shape of the target. Additionally normal vectors on this surface are included in the pixel file. ALMOST computes the response of the target echo after matched filtering, including the phase. Close range effects are fully taken into account. The ALMOST results are taken as simulator input for the Synthetic Aperture Sonar (SAS) processor, developed at TNO, as a first validity check ofALMOST. The model validity is checked further by comparing SAS results from ALMOST, with SAS results from SIMONA, a simulator for time signals, also developed at TNO. After these successful validity tests, ALMOST results for a mine-like target at close range (0.5 to 3m) are compared with measurements, obtained with a so-called “scan frame”. Identical geometry is used in ALMOST and the scan frame data, and both data sets are SAS processed. The SAS processor uses 2500 sonar positions with spacing 2mm, on a straight line, some decimetres above the target. SAS reconstructs the target shape into a two dimensional picture. Some differences between model and measurements can be explained from assumptions made in the pixel file representing the real target measurements.

Sonar
Target strengthTarget modellingSonar performanceTarget measurements

http://resolver.tudelft.nl/uuid:8eb9f55f-35d3-47a0-87a7-b72b4d9a0723

213766

Foundation for Research & Technology, Hellas

Proceedings of the 1st International Conference "Underwater Acoustic Measurements: Technologies & Results", 28th June - 1st July 2005, Heraklion, Crete, Greece

conference paper