| Summary: | 碩士 === 國立中山大學 === 海洋環境及工程學系 === 87 === Abstract:
The invention of multi-beam echo sounder system is a wonderful news for the people who have dealing with marine research and engineering. Its character of high data density gives us better understanding about the seabed topography and its change. However, the error propagation of multibeam data is hard to derive because all the sounding data is computed from related sensors. Besides, some irregular soundings or outliers indeed influence the charting result, and may spoil the quality of decision making. It may not be difficult to remove the outliers from the data measured in the absolutely flat and smooth seabed. But for the seabed with artificial reef or rocky coast, we need more logical rule to identify the anomalous data.
Most current published automatic error detection algorithms for multi-beam data rely on comparison with its neighbor soundings. Thus the efficiency of error detection is very much related to the data quality. However, our automatic error detection algorithm for multi-beam data has following characteristics. At first, we find the relationship between the beam angles and the positions where the beams hit the seabed in a profile. Secondly, the "shadow effect" caused by the features on the seabed is been investigated. Thirdly, time-based moving average algorithm was used for previous stages flagged data points by comparing with its neighbors from its adjacent line. The outliers are removed due to above mentioned prefiltering processes. And finally, the consistency of the inter-swath data and the seabed roughness were also checked by comparing inter-swath data .
The result shows that the two phases error flagging process originated from our error detection algorithm not only filter out the big mistake but detect small unreasonable soundings. However, it is found that a lot of soundings around artificial reefs don''t have enough neighbor soundings for depth accuracy estimation owing to lack of inter-swath overlay area at the second flagging phase. We can easily distinguish the depth points located on the surface of artificial reefs from outliers by overlapping two adjacent survey lines.
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