Estimate atmospheric pressure in an rsk object. Pressures must be in
decibars for this to work. First, a subset of pressures is created, in which
the range is `sap-dp`

to `sap+dp`

. Here, `sap`

=10.1325 dbar is standard
sealevel atmospheric pressure. Within this window, three measures of central
tendency are calculated: the median, the mean, and a weighted mean that has
weight given by
\(exp(-2*((p-sap)/dp)^2)\).

`rskPatm(x, dp = 0.5)`

- x
an rsk object.

- dp
Half-width of pressure window to be examined (in decibars).

A list of four estimates: `sap`

, the median, the mean, and the weighted mean.

The documentation for rsk explains the structure of
`rsk`

objects, and also outlines the other functions dealing with them.

Other things related to rsk data:
`[[,rsk-method`

,
`[[<-,rsk-method`

,
`as.rsk()`

,
`ctdFindProfilesRBR()`

,
`plot,rsk-method`

,
`read.rsk()`

,
`rsk-class`

,
`rskToc()`

,
`rsk`

,
`subset,rsk-method`

,
`summary,rsk-method`