Determination of the Threshold for Correcting the Astronomical Tide

Abstract

     This research aims to determine the threshold for correcting the astronomical tide and to study the guidelines for applying the threshold for correcting the astronomical tide in the tide table by analyzing the observed water level and the astronomical tide over a tide cycle during 1997-2016 to characterize the differences between the observed water level and the astronomical tide (Residual Levels) and then synthesized as the threshold for correcting the astronomical tide. The results showed that Residual Levels of the Sattahip Bay tide gauge station during spring tide the highest mean was 13 centimeters, during neap tide the highest mean was 19 centimeters, during the interval between spring tide and neap tide the highest average is 14 centimeters. At Songkhla tida gauge station, during spring tide the highest mean was 12 centimeters, during neap tide the highest mean was 16 centimeters, during the interval between spring tide and neap tide the highest average is 17 centimeters. At Thap Lamu Bay tide gauge station, during spring tide the highest mean was 18 centimeter, during neap tide the highest mean was 16 centimeters, during the interval between spring tide and neap tide the highest average is 16 centimeters. The Residual Levels was synthesized as the threshold for correcting the astronomical tide according to the following period: during spring tide was 1–18 centimeters, during neap tide was 3–16 centimeters, and during the interval between spring tide and neap tide was 0–16 centimeters. Then applying the threshold for correcting the astronomical tide was used to compare with the observed water level at Thap Lamu Bay tide gauge station in 2014. The results showed that the mean difference was in the range of 2-16 centimeters, the standard deviation was 0 – 1 centimeters. It shows that using the threshold for correcting the astronomical tide can make the astronomical tide more close to the observed water level.