tidem(t, x, constituents, latitude=NULL, rc=1, regress=lm,
debug =getOption("oceDebug"))sealevel object (e.g. produced by
read.sealevel or as.sealevel) or a vector of
times. In the former case, time is part is a sealevel-class object, in
which case it is inferred as t[["elevation"]]tidem will try to infer this from sl.lm, but could be for example rlm from the
class "tide", consisting ofZ0, 1 for SA, etc.M2".p value may make no sense at all, and it might
be removed in a future version of this function. Perhaps a significance
level should be presented, as in the software developed by both Foreman
and Pawlowicz.}
constituents is not provided, then the constituent
list will be made up of the 69 constituents regarded by Foreman as
standard. These include astronomical frequencies and some shallow-water
frequencies, and are as follows: c("Z0", "SA", "SSA", "MSM", "MM",
"MSF", "MF", "ALP1", "2Q1", "SIG1", "Q1", "RHO1", "O1", "TAU1", "BET1",
"NO1", "CHI1", "PI1", "P1", "S1", "K1", "PSI1", "PHI1", "THE1", "J1",
"SO1", "OO1", "UPS1", "OQ2", "EPS2", "2N2", "MU2", "N2", "NU2", "GAM2",
"H1", "M2", "H2", "MKS2", "LDA2", "L2", "T2", "S2", "R2", "K2", "MSN2",
"ETA2", "MO3", "M3", "SO3", "MK3", "SK3", "MN4", "M4", "SN4", "MS4",
"MK4", "S4", "SK4", "2MK5", "2SK5", "2MN6", "M6", "2MS6", "2MK6",
"2SM6", "MSK6", "3MK7", "M8").} constituents is the string
"standard", then a provisional list is set up as in Case 1, and
then the (optional) rest of the elements of constituents are
examined, in order. Each of these constituents is based on the name of a
tidal constituent in the Foreman (1977) notation. (To get the list,
execute data(tideData) and then execute cat(tideData$name).)
Each named constituent is added to the existing list, if it is not already
there. But, if the constituent is preceeded by a minus sign, then it is
removed from the list (if it is already there). Thus, for example,
constituents=c("standard", "-M2", "ST32") would remove the M2
constituent and add the ST32 constituent.}
"standard", then the list of
constituents is processed as in Case 2, but without starting with the
standard list. As an example, constituents=c("K1", "M2") would fit
for just the K1 and M2 components. (It would be strange to use a minus
sign to remove items from the list, but the function allows that.)}
In each of the above cases, the list is reordered in frequency prior to the
analysis, so that the results of summary.tidem will be in a
familiar form.
Once the constituent list is determined, tidem prunes the elements of
the list by using the Rayleigh criterion, according to which two
constituents of frequencies $f_1$ and $f_2$ cannot be
resolved unless the time series spans a time interval of at least
$rc/(f_1-f_2)$. The value rc=1 yields nominal
resolution.
A list of constituent names is created by the following: data(tidedata) print(tidedata$const$name)
The text should include discussion of the (not yet performed) nodal correction treatement.
Leffler, K. E. and D. A. Jay, 2009.
Enhancing tidal harmonic analysis: Robust (hybrid) solutions.
Continental Shelf Research, 29(1):78-88.
Pawlowicz, Rich, Bob Beardsley, and Steve Lentz, 2002.
Classical tidal harmonic analysis including error estimates in MATLAB using T_TIDE.
Computers and Geosciences, 28, 929-937.
summary.tidem summarizes a "tide" object,
plot.tidem plots one, and predict.tidem
makes predictions from one. As for the input, sealevel objects may be
created with as.sealevel or read.sealevel. See
notes at sealevelTuktoyaktuk, which is test data set.library(oce)
# The demonstration time series from Foreman (1977),
# also used in T_TIDE (Pawlowicz, 2002).
data(sealevelTuktoyaktuk)
tide <- tidem(sealevelTuktoyaktuk)
summary(tide)
# AIC analysis
extractAIC(tide[["model"]])
# Fake data at M2
t <- seq(0, 10*86400, 3600)
eta <- sin(0.080511401 * t * 2 * pi / 3600)
sl <- as.sealevel(eta)
m <- tidem(sl)
summary(m)Run the code above in your browser using DataLab