# tr_ctd

##

Last updated Fri Nov 19 12:59:39 1999

Interpolate CTD at ADCP transducer depth

## 1. USAGE

tr_ctd control_file

## 2. DESCRIPTION

This utility interpolates CTD data at Adcp transducer depth and profile times or positions, creating a list of temperature and salinity values. These can then be used to calibrate the speed of sound.

For each time range listed in the control file, tr_ctd will read CTD profiles from a CODAS database and interpolate temperature and salinity values at the given transducer depth. It will then regrid these values to the specified ADCP positions or times and print them to the output files.

## 3. PARAMETERS

The control file must define the following parameters:

year_base: YYYY

  Year base to be used for converting time into decimal days. This value must correspond to the dates listed in the file specified by parameter nav_file.

dbname: name

  Name (with path) of CTD database containing the profiles to process.

nav_file: file

  Name of file containing ADCP profile times and positions. It has the same format as the output from getnav.

tr_depth: float

  Estimated transducer depth in meter.

x_axis: keyword

  Keyword specifying the interpolation axis of CTD data. Possible values are time, longitude and latitude. If CTD data have been collected with a CTD SeaSoar together with ADCP data, then time is probably the best choice. If calibration of sound speed must be carried out with data from a separate section, position values along the section must be chosen.

output name

  Base name (with path) for output files.

## 4. OPTIONS

In addition to the parameters listed above, the following options are available:

OPTIONS:

  This key word can be used to improve the clarity of the control file and specify the beginning of options. It has no effect.

steps: n

  Number of profiles to step within the CTD database.

z_gap: float

  When regriding CTD profile data to transducer depth, a call to fill_gaps is performed. If the distance from the next good data to transducer depth is too large, vertical filling is not a good idea, but horizontal interpolation with adjacent profiles will give a better result. You can adjust this by specifying the maximal allowed vertical gap (in the units of CTD pressure) for vertical filling.

lon_180

  Specify this for converting longitude values between -180 and +180 degree before using them.

end

  This keyword is mandatory and terminates the list of selected options.

## 5. TIME RANGES

Finally, the control file is terminated by a list of time ranges. See time_rng(5) for the syntax of these.

## 6. OUTPUT FILES

Two files are generated. They have the name specified by parameter output, but the one with suffix tem contains interpolated temperature values, while the one with suffix sal contains interpolated salinity values. The format of these files is the same and has the following columns:

1. ADCP time in decimal days, sorted in ascending order
2. Interpolated CTD values (temperature or salinity)
3. ADCP longitude in decimal degree
4. ADCP latitude in decimal degree

## 7. AUTHOR

- Pierre Jaccard, Geophysical Institute, University of Bergen, 1999

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