By comparing their shapes, distribution and height we can distinguish noises from fish heavens. Where artificial features presumably exists such as dredged area or wharf frontage, same step is required. To avoid this, we need to limit range to adopt soundings in the swath. GPS gyro is also useful. Correction of ray refraction may be incomplete because measurement of sound velocity is usually performed once a day.
Beams formed by circular array is sensitive to surface sound velocity.
Surveying with multibeam echo sounding is efficient, but on the other hand its enormous data takes too much time to process. More efficient multibeam editor is requested. In addition, detecting method of abnormal data should be developed. Fig.8 Comparison of soundings acquired by multibeam and single beam echosounders. Fig.9 Comparison of soundings acquired by multibeam and single beam echosounders.