The ABCS Program for the Analysis of Echo Sounder Returns for ...

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δr 1 r 2d 2DSTO-GD-0215To see how the returned ping can change duration as the seafloor depth differs,consider the same source ping insonifying the seafloor at two different depths to anangle of 2θ (see Figure 14). The wave fronts produced by the source will be spherical inshape. The leading edge of the ping will be insonifying the seafloor at an angle θ andthere will be some point (point A in Figure 14) in the source ping that is just about tostart insonifying the seafloor, with time between these two points being δt.Sinceδt 1 = c δr 1 , δt 2 = c δr 2eq(7)anddCosθwhere c = radial speed of soundδr =the distance between the pointsd = depth12δ r1 = − d1, r2 = − d2dδ eq(8)CosθSea surfacer 1θ d 1θPoint A δr 2SeafloorFigure 14: Two different depths with the same insonified angle, when the insonified area is acircle.Combining eq(7) and eq(8) gives:d2δ t2 = δt1eq(9)d1The leading edgeThe leading edge Point A24
DSTO-GD-0215Therefore the time taken to insonify the seafloor to a specific angle after the start ofthe ping first hits the seafloor takes longer for deeper water. The return path back tothe hydrophone will have a similar delay. For a constant sampling rate, more sampleswill be taken before a particular angle is reached for a deeper bottom compared to ashallower bottom. Therefore the deeper the water the longer the duration of thereturned pulse (see Figure 15). This result also holds for an insonified annulus on theseafloor.PowerDepth=d1d2>d1 Dilated returnd1
Page 1 and 2: The ABCS Program for the Analysis o
Page 3: The ABCS Program for the Analysis o
Page 7 and 8: DSTO-GD-02151. IntroductionThe type
Page 9 and 10: DSTO-GD-02153.1 Depth Normalisation
Page 11 and 12: DSTO-GD-0215By combining these two
Page 13 and 14: DSTO-GD-02153.1.3 Effect of Transfo
Page 15 and 16: DSTO-GD-0215If a longer ping durati
Page 17 and 18: DSTO-GD-0215SamplingRate =2 × Soun
Page 19 and 20: DSTO-GD-0215If a return is not foun
Page 21 and 22: DSTO-GD-0215The FFT plot was calcul
Page 23 and 24: DSTO-GD-0215Figure 10 : Statistics
Page 25 and 26: DSTO-GD-02153.4 Problems found from
Page 27 and 28: DSTO-GD-0215R.E. Francois and G.R.
Page 29: DSTO-GD-0215Appendix 1: Returned Pi
Page 33 and 34: DSTO-GD-0215Appendix 2: Geometric E
Page 35 and 36: DSTO-GD-0215Appendix 3: The ‘Leve
Page 37 and 38: DSTO-GD-02151st input2nd inputRetur
Page 39 and 40: DSTO-GD-0215Appendix 4: Calculation
Page 41 and 42: DSTO-GD-0215Substituting y=µSinω
Page 43 and 44: DSTO-GD-0215dB P= Sinθeq(21)dθ2Th
Page 45 and 46: DSTO-GD-0215Calculating the Insonif
Page 47 and 48: DSTO-GD-0215Appendix 5: Search Area
Page 49 and 50: DISTRIBUTION LISTThe ABCS Program f
Page 51: Page classification: UNCLASSIFIEDDE

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