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The apparent water depth obtained by photogrammetric measurement appears to be shallower than true depth. This is because the reflected sun-rays from the sea-bottom refract at the water's surface.<BR>In order to convert the water depth observed by aerial photographs to true depth, it is necessary to obtain correction factors. Equation (2), derived by G.C. Twinkel, determines the correction factors; equation (3), derived by J.G. Meijer, transforms the correction factors of equation (2) so that they may be used for numerical calculation by digital computer. In this study, the computer programs based on the above equations were successful. (During the study, A-7 plotting equipment was used for analyzing the aerial photographs.)<BR>The two areas covered by the aerial photographs were: 1. off-shore, near Omaezaki Port, Shizuoka Prefecture; 2. Amatsu Port, Chiba Prefecture. Both areas are located in Japan.<BR>The water depths observed from the aerial photographs were corrected to true depths by digital computer. The calculated true depths were compared with the water depth results recorded by echo-sounding. The results of this comparison were as follow:<BR>1) The apparent water depths obtained by photographs measured deeper than those obtained by echo-soundings.<BR>2) The mean differences of the water depths obtained by aerial photographs and echosoundings were 13.9cm in the Omaezaki area (within 500m from the shoreline) and 5.4cm at Amatsu Port.<BR>3) The mean water depths by echo-soundings were 3.24m off-shore Omaezaki and 0.62m at Amatsu Port. Consequently, the relative errors were within a ±30% maximum range (and were mostly a ±10% range) .<BR>4) As relative orientation of the stereo model of Amatsu Port was complete, we were able to carry out statistical test of the differences between the independent samples. Results showed that the distinct differences between these two methods of measurement were not recognized.<BR>Conclusion; The application of photogrammetry to water depth measurement is practicable and may prove valuable in near-shore and/or reef zone areas where it is difficult to reach such arenas by observation boat.
- 社団法人 日本写真測量学会の論文
社団法人 日本写真測量学会 | 論文
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