extrema {Tides}

Extrema

Description

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.

Usage

extrema(h, h0, T2 = 5*60*60, hoffset = 0, filtconst = 1)

Arguments

h

Water level time series. Data frame with time and h column

h0

Reference level, either single valued vector with dimension corresponding to h

T2

'Lower' bound on half the quasi period, but higher than expected stagnant phase; default = 5h

hoffset

Offset level, to prevent spurious maxima generation due to small fluctuations

filtconst

Filtering constant for smoothing the time series with filter(x, rep(1/filtconst,filtconst))

Value

a list containing:

HL

Data frame with time, water level and reference level of the extrema. Column HL denotes H(igh) (=maximum) or L(ow) (=minimum) water levels

h

Original water level data frame with additional columns HL, denoting H(igh) or L(ow) water phase and N(umber) of tidal cycle.

Author(s)

Tom Cox <tom.cox@untwerpbe>