Tidal analysis

Citation

Loughlin, C. (2009), "Tidal analysis", Sensor Review, Vol. 29 No. 3. https://doi.org/10.1108/sr.2009.08729caa.001

Tidal analysis

Article Type: Editorial From: Sensor Review, Volume 29, Issue 3

I have developed an interest in tides to support my nautical endeavours and have found them to be very complicated indeed. The tides that we experience are based on a variety of astronomical activities from the position of the moon (the biggest influence) and the sun (about half the influence of the moon).

Astronomical events are interesting because, on one hand, everything is highly predictable and on the other, everything constantly varies. The sun and the moon both change their distance from the earth as well as their relative orbital phases and their declination (angle to the plane of the earth’s rotation).

Vice-Admiral Robert Fitzroy, the originator of weather forecasting and Darwin’s captain on the Beagle, committed suicide after a long bout of depression aggravated by his lack of success in making accurate weather forecasts. I would be surprised if early practitioners of tidal prediction did not consider the same fate.

I have tried to establish easily explainable links between, for example, the highest tides of the year and various astronomical positions and have failed dismally to get anything close to reality. It turns out that over 300 factors need to be taken into account before a reasonable accuracy can be obtained.

Fundamentally, tides are waveforms, and Fourier analysis is needed to separate the individual frequency components and determine the rules on which future predictions can be based.

However, given this analysis, good accuracies can be obtained and tides do become reasonably predictable, although the weather (whose prediction thwarts the endeavours of supercomputers) plays a role, as high and low pressures, respectively, give rise to lower and higher tides than those predicted.

Someone tasked with generating tide tables without access to external sources of information, would soon work out that the phase of the moon played a significant role (as full moons equate to higher tides and half-moons to lower). And after ten years of painstaking recording might also note that tides around January (when the earth is closest to the sun) tended to have a still larger range.

However, apart from these advances, our lone tidesman would be puzzled by seemingly random variations and as such will no doubt gain the sympathy of many an industrial engineer struggling to make sense of their own data.

Tidal height calculations require inputs of many sources of sensor data, from astronomical positions to barometric pressure and Coriolis forces. However, – given that these data have been obtained, the real world effects can be analyzed and predicted.

The main point of all the above is that any output from a system can only be predicted if you have an understanding of the sources of inputs. If your industrial manufacturing system is not behaving as you expect or want, then it is likely that you are not seeing the full picture of controlling influences.

You need to be able to measure all the relevant inputs if you are going to be able to understand the output. But if you can obtain this data and analyze the output with reference to it, then you will almost certainly gain a greater understanding of the process you are trying to control.

Clive Loughlin