36 | Berichte des BSH Nr. 57 
3.4 
Practical 
information on 
the calculation 
The main programming steps for analysing the semi-monthly inequality and cal- 
culating the tidal parameters are summarized as follows: 
1. 
2. 
Read data: Times and heights of high and/or low water. 
If necessary, convert the times to UTC and the heights to a standardised 
height level. 
Filter out the high and low water levels that are marked as influenced by 
the authority operating the tide gauge. 
Determine whether there is enough data for an independent analysis 
or whether a reference-based calculation must be carried out 
‘see section 3.2). 
Ifa reference-based calculation is necessary, repeat the procedure from 
step 1 with the data of the reference tide gauge (up to step 11). 
Assign the lunar transit number to the high and low water levels. The 
transit number counts the number of transits of the Moon through the 
prime meridian, whereby the Oth transit was set to 31 December 1949 
{21:08 UT) (Müller-Navarra, 2009). The transit number makes it easier to 
sort and organise the high and low waters. However, the analysis of the 
semi-monthly inequality can in principal also be carried out without the 
assignment of transit numbers. 
Calculation of the tidal intervals: the transit times of the (true) moon at the 
prime meridian are subtracted from the times of high and low water. 
Filter out the high and low water that deviate more than three standard 
deviations in height or interval from the respective mean value. 
In case of a reference-based calculation, subtract the data from the refer- 
ence tide gauge (see section 3.2) 
Modelling of the semi-monthly inequality (see section 3.1) in two itera- 
tions with 3-sigma clipping after the first run. 
\Alhen calculating the reference tide gauge: save the analysis results and 
continue with the data of the subordinate tide gauge in step 6. 
Optional: Calculate the uncertainties on the model parameters, e.g. via 
Markov-Chain-Monte-Carlo analysis. 
ın case of a reference-based calculation, calculate the final coefficients 
as the sum of the coefficients of the reference-based calculation and the 
coefficients for the reference tide gauge (see section 3.2) 
Determine the times of the maxima and minima in the course of the semi- 
monthly inequality (T1, T2, T3, T4 in Table 1) 
Calculation of the tidal parameters from model parameters according to 
Table 1. 
3 
4 
5 
6. 
7 
8 
9. 
10. 
11. 
12. 
13. 
14. 
15.