This function is intended to provide a bridge to predict.tidem(), enabling tidal predictions based on published tables of harmonic fits.

as.tidem(tRef, latitude, name, amplitude, phase, debug = getOption("oceDebug"))

Arguments

tRef

a POSIXt value indicating the mean time of the observations used to develop the harmonic model. This is rounded to the nearest hour in as.tidem(), to match tidem().

latitude

Numerical value indicating the latitude of the observations that were used to create the harmonic model. This is needed for nodal-correction procedures carried out by tidemVuf().

name

character vector holding names of constituents.

amplitude

Numeric vector of constituent amplitudes.

phase

Numeric vector of constituent Greenwich phases.

debug

an integer specifying whether debugging information is to be printed during the processing. This is a general parameter that is used by many oce functions. Generally, setting debug=0 turns off the printing, while higher values suggest that more information be printed. If one function calls another, it usually reduces the value of debug first, so that a user can often obtain deeper debugging by specifying higher debug values.

Value

An object of tidem, with only minimal contents.

Details

Note that only constituent names known to tidem() are handled. The permitted names are those listed in Foreman (1978), and tabulated with

data(tidedata)
data.frame(name=tidedata$const$name, freq=tidedata$const$freq)

Warnings are issued for any constituent name that is not in this list; as of the late summer of 2019, the only example seen in practice is M1, which according to Wikipedia (2019) has frequency 0.0402557, which is very close to that of NO1, i.e. 0.04026859, perhaps explaining why Foreman (1978) did not handle this constituent. A warning is issued if this or any other unhandled constituent is provided in the name argument to as.tidem().

Known issues

There are two known differences between tidem() and the Matlab T_TIDE package, as listed in references 3 and 4. Work on these issues is planned for the summer of 2020.

References

  1. Foreman, M. G. G., 1978. Manual for Tidal Currents Analysis and Prediction. Pacific Marine Science Report. British Columbia, Canada: Institute of Ocean Sciences, Patricia Bay.

  2. Wikipedia, "Theory of Tides." https://en.wikipedia.org/wiki/Theory_of_tides Downloaded Aug 17, 2019.

  3. Github issue 1653: tidem() and t_tide do not produce identical results https://github.com/dankelley/oce/issues/1653

  4. Github issue 1654: predict(tidem()) uses all constituents, unlike T_TIDE https://github.com/dankelley/oce/issues/1654

See also

Examples

# Simulate a tide table with output from tidem(). data(sealevelTuktoyaktuk) # 'm0' is model fitted by tidem() m0 <- tidem(sealevelTuktoyaktuk)
#> Note: the tidal record is too short to fit for constituents: SA SSA MSM MF SIG1 RHO1 TAU1 BET1 CHI1 PI1 P1 S1 PSI1 PHI1 THE1 SO1 OQ2 2N2 NU2 GAM2 H1 H2 MKS2 LDA2 T2 R2 K2 MSN2 SO3 MK4 SK4 2MK6 MSK6
p0 <- predict(m0, sealevelTuktoyaktuk[["time"]]) m1 <- as.tidem(mean(sealevelTuktoyaktuk[["time"]]), sealevelTuktoyaktuk[["latitude"]], m0[["name"]], m0[["amplitude"]], m0[["phase"]]) # Test agreement with tidem() result, by comparing predicted sealevels. p1 <- predict(m1, sealevelTuktoyaktuk[["time"]]) expect_lt(max(abs(p1 - p0), na.rm=TRUE), 1e-10) # Simplified harmonic model, using large constituents # > m0[["name"]][which(m[["amplitude"]]>0.05)] # [1] "Z0" "MM" "MSF" "O1" "K1" "OO1" "N2" "M2" "S2" h <- " name amplitude phase Z0 1.98061875 0.000000 MM 0.21213065 263.344739 MSF 0.15605629 133.795004 O1 0.07641438 74.233130 K1 0.13473817 81.093134 OO1 0.05309911 235.749693 N2 0.08377108 44.521462 M2 0.49041340 77.703594 S2 0.22023705 137.475767" coef <- read.table(text=h, header=TRUE) m2 <- as.tidem(mean(sealevelTuktoyaktuk[["time"]]), sealevelTuktoyaktuk[["latitude"]], coef$name, coef$amplitude, coef$phase) p2 <- predict(m2, sealevelTuktoyaktuk[["time"]]) expect_lt(max(abs(p2 - p0), na.rm=TRUE), 1) par(mfrow=c(3, 1)) oce.plot.ts(sealevelTuktoyaktuk[["time"]], p0) ylim <- par("usr")[3:4] # to match scales in other panels oce.plot.ts(sealevelTuktoyaktuk[["time"]], p1, ylim=ylim) oce.plot.ts(sealevelTuktoyaktuk[["time"]], p2, ylim=ylim)