What has been changed by the digital processing of sea level data?

Abstract

In the 20th century, tidal curves were recorded on papers at most of the tide stations. The times in the records were not accurate mainly due to the unreliable handling of the recording paper. The hourly heights of the sea level were derived from the smoothing curves, which were drawn on tidal curves by the personnel. The data quality of the hourly heights depended on the capability of the personnel in charge of the data processing at the tide stations. At present, sea level data at most of tide stations are recorded and processed digitally. The times of records are now accurate and high frequency components are removed by digital low-pass filters. The data quality of the hourly heights does not depend on the capability of the personnel and has become better than ever. The digital processing of sea level data may have increased the quality of the records produced at the tide stations. In this paper, the improvement of the data quality of hourly heights is shown by comparing the differences in the hourly heights between neighboring tide stations in the past and the present.