Abstract:

New and existing estimators of the “Echo Value Constant” based on split-beam detected and integrated single target echoes in the “alternative echo integration method” have been compared by using acoustic data. Two new estimators were made to make consideration to the fact that the detected echo strengths of single targets outside the half power angle of the split beam transducer have positive average bias. Another new estimator that was proposed in a previous paper of the same author is, however, not of this type, and seems in general to be positively biased. The other new estimators seems to be better with respect to the bias than the old one, but one of them seems to be a bit unstable with significant negative bias in special cases. There may be developed even better, nearly beam independent, estimators of the Echo Value Constant.

“In situ” single echo Target Strengths, although not used, are computed, and these indicate that the increasing average positive bias with increasing beam angle is not dramatic within the angle of -10 dB transmit beam damping.