Calculate maxima and minima of quasi periodic time series. The function works good when the time series is 'smooth enough'. The function will fail when multiple local extrema exist, with a magnitude similar to the extremum extremorum and in an interval larger than [t-T2, t+T2] around the extremum extremorum at time t. When this is the case, this might be solved by adding extra wrappers around the function.
extrema(h, h0, T2 = 5*60*60, hoffset = 0, filtconst = 1)Water level time series. Data frame with time and h column
Reference level, either single valued vector with dimension corresponding to h
'Lower' bound on half the quasi period, but higher than expected stagnant phase; default = 5h
Offset level, to prevent spurious maxima generation due to small fluctuations
Filtering constant for smoothing the time series with filter(x, rep(1/filtconst,filtconst))
a list containing:
Data frame with time, water level and reference level of the extrema. Column HL denotes H(igh) (=maximum) or L(ow) (=minimum) water levels
Original water level data frame with additional columns HL, denoting H(igh) or L(ow) water phase and N(umber) of tidal cycle.