海洋調査技術　第11巻　2号　1999年9月

Fig. 4. Occurrence frequency of the ratio (%) of reported maximum observation depth to water depth.

Fg. 5. Yearly variation of the occurrence frequency of erroneous maximum observation depth. The frequencies for various excess ratios (the maximum observation depth divided by water depth) are shown by different shades:no shade (white) for excess ratio from 10 to 125%, the light shade from 125 to 190%, medium shade frorn 190 to 260%, and heavy shade larger than 260%. The large excess ratio appears mainly in the years between 1974 and 1977, when mismatched data sheets were used.

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