The 20 mm thickness block has been used with 20 mm and 100 mm water paths. For the 20 mm water path, only 3 backwall echoes have correctly been measured, the remaining ones are distrupted by the second surface echo, due to the low water path relative to the block thickness and are not simulated by the CIVA models.
Results are calibrated from a Ø2 mm SDH, located at 28 mm depth and a 20 mm water path. Amplitudes of the surface echo (echo n°0), of the first backwall echo (echo n°1) and of the following backwall echoes are plotted below in black for experimental measurements, in red for Kirchhoff model results and in blue for specular model results.
Both models are very similar and overestimate echoes amplitudes versus measurements with 4 dB for the surface echo and the first backwall echo, and up to 6 dB for the ninth echo in the case of 100 mm water path. The discrepancy slightly increases with the number of rebounds.
The Ascans are represented below in the case of 20 mm water path for the surface echo and the three measured backwall echoes. The red curve corresponds to Kirchhoff model, the blue one to the specular model and the black one to measured results.
Both CIVA models predict correctly the three backwall echoes but less accurately the surface echo.
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