Assemble data into a ctd object. This function is complicated (spanning approximately 500 lines of code) because it tries to handle many special cases, and tries to make sensible defaults for unspecified parameters. If odd results are found, users might find it helpful to call this function with the first argument being a simple vector of Practical Salinity values, in which case the processing of the other arguments is relatively straightforward.
as.ctd( salinity, temperature = NULL, pressure = NULL, conductivity = NULL, scan = NULL, time = NULL, units = NULL, flags = NULL, missingValue = NULL, type = "", serialNumber = NULL, ship = NULL, cruise = NULL, station = NULL, startTime = NULL, longitude = NULL, latitude = NULL, deploymentType = "unknown", pressureAtmospheric = 0, sampleInterval = NULL, profile = NULL, debug = getOption("oceDebug") )
may be (1) a numeric vector holding Practical Salinity,
(2) a list or data frame holding
salinity and other
hydrographic variables or (3) an
oce-class object that holds
hydrographic information. If
salinity is not provided,
conductivity must be provided, so that
can be used to compute salinity.
a numeric vector containing in-situ temperature in
\(^\circ\)C on the ITS-90 scale; see “Temperature units” in the
a numeric vector containing sea pressure values, in decibars.
Typically, this vector has the same length as
but it also possible to supply just one value, which will be repeated
to get the right length. Note that
as.ctd() stores the
pressureAtmospheric in the returned object,
although the default value for
pressureAtmospheric is zero, so
in the default case,
pressure is stored directly.
an optional numeric vector containing electrical conductivity ratio through the water column. To convert from raw conductivity in milliSeimens per centimeter divide by 42.914 to get conductivity ratio (see Culkin and Smith, 1980).
optional numeric vector holding scan number. If not provided,
this is set to seq_along
optional vector of times of observation.
an optional list containing units. If not supplied,
defaults are set for
conductivity. Since these are simply guesses, users
are advised strongly to supply
units. See “Examples”.
if supplied, this is a list containing data-quality flags. The elements of this list must have names that match the data provided to the object.
optional missing value, indicating data that should be
NA. Set to
NULL to turn off this feature.
optional type of CTD, e.g. "SBE"
optional serial number of instrument
optional string containing the ship from which the observations were made.
optional string containing a cruise identifier.
optional string containing a station identifier.
optional indication of the start time for the profile,
which is used in some several plotting functions. This is best given as a
POSIXt time, but it may also be a character string
that can be converted to a time with
UTC as the timezone.
optional numerical value containing longitude in decimal
degrees, positive in the eastern hemisphere. If this is a single number,
then it is stored in the
metadata slot of the returned value; if it
is a vector of numbers, then they are stored in the
optional numerical value containing the latitude in decimal
degrees, positive in the northern hemisphere. See the note on length, for
character string indicating the type of deployment. Use
"unknown" if this is not known,
"profile" for a profile (in
which the data were acquired during a downcast, while the device was lowered
into the water column, perhaps also including an upcast;
the device is installed on a fixed mooring,
"tsg") if the device is mounted on a moving vessel, to record
near-surface properties, or
"towyo" if the device is repeatedly
lowered and raised.
A numerical value (a constant or a vector),
that is subtracted from pressure before storing it in the return value.
(This altered pressure is also used in calculating
that is to be computed from
conductivity, etc., using
optional numerical value indicating the time between samples in the profile.
optional positive integer specifying the number of the profile
to extract from an object that has data in matrices, such as for some
argo objects. Currently the
profile argument is only utilized for
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
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
A ctd object.
The following sections provide an some notes on how
certain object types given as the first parameter.
Converting argo objects
salinity argument is an object of argo, then that
object is dismantled and reassembled as a ctd object in ways that
are mostly straightforward, although the handling of time depends
on the information in the original netcdf data file that was used
read.argo() to create the argo object.
All Argo data files contain an item called
juld from which the profile
time can be computed, and some also contain an additional item named
from which the times of individual measurements can also be computed. Both
cases are handled by
as.ctd(), using a scheme outlined in
Note 4 of the Details section of the
Converting rsk objects
salinity argument is an object of rsk,
as.ctd passes it,
rsk2ctd(), which builds the ctd object that is
as.ctd. The other arguments to
are ignored in this instance, because
rsk objects already
contain their information. If required, any data or metadata
element can be added to the value returned by
The returned rsk object contains pressure in a form that
may need to be adjusted, because
rsk objects may contain
either absolute pressure or sea pressure. This adjustment is handled
as.ctd, by examination of the metadata item
pressureType (described in the documentation for
read.rsk()). Once the sea pressure is determined,
adjustments may be made with the
although in that case it is better considered a pressure adjustment
than the atmospheric pressure.
rsk objects may store sea pressure or absolute pressure (the
sum of sea pressure and atmospheric pressure), depending on how the object was
ctd objects store sea pressure, which is needed for
plotting, calculating density, etc. This poses no difficulties, however,
as.ctd automatically converts absolute pressure to sea pressure,
if the metadata in the rsk object indicates that this is
appropriate. Further alteration of the pressure can be accomplished with the
pressureAtmospheric argument, as noted above.
Culkin, F., and Norman D. Smith, 1980. Determination of the concentration of potassium chloride solution having the same electrical conductivity, at 15 C and infinite frequency, as standard seawater of salinity 35.0000 ppt (Chlorinity 19.37394 ppt). IEEE Journal of Oceanic Engineering, volume 5, pages 22-23.
Other things related to ctd data:
library(oce) # 1. fake data, with default units pressure <- 1:50 temperature <- 10 - tanh((pressure - 20) / 5) + 0.02*rnorm(50) salinity <- 34 + 0.5*tanh((pressure - 20) / 5) + 0.01*rnorm(50) ctd <- as.ctd(salinity, temperature, pressure) # Add a new column fluo <- 5 * exp(-pressure / 20) ctd <- oceSetData(ctd, name="fluorescence", value=fluo, unit=list(unit=expression(mg/m^3), scale="")) summary(ctd) #> CTD Summary #> ----------- #> #> * Data Overview #> #> Min. Mean Max. Dim. NAs #> scan 1 25.5 50 50 0 #> salinity [PSS-78] 33.489 34.108 34.516 50 0 #> temperature [°C, ITS-90] 8.9501 9.7841 11.029 50 0 #> pressure [dbar] 1 25.5 50 50 0 #> fluorescence [mg/m³] 0.41042 1.7903 4.7561 50 0 #> #> * Processing Log #> #> - 2023-09-21 15:03:33 UTC: `create 'ctd' object` #> - 2023-09-21 15:03:33 UTC: `as.ctd(salinity = salinity, temperature = temperature, pressure = pressure)` #> - 2023-09-21 15:03:33 UTC: `oceSetData(object = ctd, name = "fluorescence", value = fluo, unit = list(unit = expression(mg/m^3), scale = ""))` # 2. fake data, with supplied units (which are the defaults, actually) ctd <- as.ctd(salinity, temperature, pressure, units=list(salinity=list(unit=expression(), scale="PSS-78"), temperature=list(unit=expression(degree*C), scale="ITS-90"), pressure=list(unit=expression(dbar), scale="")))