oce (version 0.1.67)

ctd.trim: Trim start/end portions of a CTD cast

Description

Trim start/end portions of a CTD cast.

Usage

ctd.trim(x, method="downcast",parameters=NULL, verbose=FALSE)

Arguments

x

A ctd object, e.g. as read by read.ctd.

method

Various methods exist, some of which use parameters: "downcast"{Select only data for which the CTD is descending. This is done in stages.

1. The pressure data are despiked with a smooth() filter with method "3R". This remov

parameters

Depends on method; see above.

verbose

If set to TRUE, some debugging information is provided.

Value

• A new ctd object.

Details

For a quick look at the data, the method="downcast" scheme is normally quite adequate. However, a wise user will seek want to exert more control over the trimming process. Visual inspection is a good way to do this, using plot.ctd.scan() together with ctd.trim. Normally, this involves identifying by eye an initial period in which the CTD is in the air or unequilibrated in the water, and a final period in which the CTD is no longer descending. Quite often this final period is easier to find by eye than with the downcast method, since the instrument operator may leave the device in deep water for some extra time to fire off a water bottle, etc., yielding problematic CTD data (but with some wonderful chemical or biological samples).

References

The Seabird CTD instrument is described at http://www.seabird.com/products/spec_sheets/19plusdata.htm.

See Also

The ctd object may be read with read.ctd. plot.ctd.scan is very useful in providing guidance for trimming with ctd.trim.

Examples

library(oce)
data(ctd) 
ctd.trimmed <- ctd.trim(ctd, "pressure", c(3, 5))
summary(ctd.trimmed)