The Van de Casteele test revisited:: An efficient approach to tide gauge error characterization

The classical question of metrology related to the quality of the tide gauge measurements has become more important this last decade or so as new technologies have emerged and tide gauge networks are modernized. The Global Sea Level Observing System (GLOSS) target of 1-cm accuracy in the individual sea level measurement is motivated by more demanding applications than the traditional hydrographic works and tide predictions, for instance, the monitoring of the long-term trends in sea level or the calibration of satellite radar altimeters. To examine and further assess the performance of modern tide gauge measurements, the Van de Casteele test is revisited. This test is based on a diagram plotting readings taken with a reference probe against the tide gauge readings over at least one tidal cycle. The application of the test to different sets of data at different locations in the world under different environmental conditions shows the test as a simple procedure that immediately gives a qualitative and quantitative illustration of the errors involved in the sea level measurement, capable of sensing the presence of a fault with whatever tide gauge technology is involved. It is recommended that such quality control tests are brought back into fashion and are conducted on a regular basis, in particular following the upgrading of the tide gauge stations.