2.6 Application to Aircraft Structures
45
Fig. 2.18 Fastener with multisite damage. Reconstructed with 4 × 4 transmitter scan and 32 × 32
receiver scan, using the stest estimator. Noise: 1% relative magnitude error; 1 ◦ phase error
ratio of the largest to the smallest value of S is not large, typically five or less. On the
other hand, the minimum for cell no. 86 is quite sharply peaked at a value of −0.86,
which is quite close to its ‘correct’ value of −0.84. Furthermore, the minimum is
much deeper than that for cell no. 87. This, then, is the basis of our heuristic rule:
if host cells and anomalous cells occupy the same layer, the host cells are quite
poorly resolved compared to the anomalous cells. Hence, when we see curves
such as those in Fig. 2.20, we will assume that cells, such as no. 87, for which
45
Fig. 2.18 Fastener with multisite damage. Reconstructed with 4 × 4 transmitter scan and 32 × 32
receiver scan, using the stest estimator. Noise: 1% relative magnitude error; 1 ◦ phase error
ratio of the largest to the smallest value of S is not large, typically five or less. On the
other hand, the minimum for cell no. 86 is quite sharply peaked at a value of −0.86,
which is quite close to its ‘correct’ value of −0.84. Furthermore, the minimum is
much deeper than that for cell no. 87. This, then, is the basis of our heuristic rule:
if host cells and anomalous cells occupy the same layer, the host cells are quite
poorly resolved compared to the anomalous cells. Hence, when we see curves
such as those in Fig. 2.20, we will assume that cells, such as no. 87, for which