process

1. USAGE

process control_file

2. DESCRIPTION

This utility averages NB raw ADCP pings and load them into a CODAS database. It is currently designed to load data as defined in producer definition file adcp_hm.def. See below for the syntax of the control_file.

3. PARAMETERS

The following parameters are required:

year_base: YYYY

Specify the year base to use for converting dates in decimal days. Since the format of NB ADCP raw files does not contain full dates with year, a good choice for this parameter is to choose the year during which measurements were carried out.

file_list: file

Name of file containing successive names (including path) of NB ADCP raw files to average. This file can contain C-syntax comments.

log_file: file

Name of file for log information.

db_name: name

Name of database with path. Remember that the base name of a CODAS database can only be made of five characters and that suffixes are added automatically

prd_file: file

Producer definition file. This is the file containing the content of the database.

avg_time: seconds

Averaging time in seconds.

4. OPTIONS

The rest of the averaging process is controlled by the following options:

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.

use_scan_nav:

Specify that navigation data should be read from a file generated by scan_nav(1). This file contains pre-processed navigation data synchronized with ADCP pings. The following sub-options are available:

file: file

Name of file (with path) containing pre-processed navigation data.

time

Use time from the navigation file as the ping time. Default is to use the one from the raw file.

heading

Use heading from the navigation file as the ping heading. Default is to use the one from the raw file.

pitch

Use pitch from the navigation file as the ping pitch. Default is to use the one from the raw file.

roll

Use roll from the navigation file as the ping roll. Default is to use the one from the raw file.

time_ref: ref_keyword

Specify which ensemble time to load into the database. Possible keywords are:

ensemble_start

The time loaded into the database will correspond to the start of ensembles.

ensemble_stop

The time loaded into the database will correspond to the end of ensembles. This is the default because most applications in the CODAS package are designed for this. It is therefore a natural choice here. Choose another reference if you know what you are doing.

end

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

nav_output:

This options allows to generate a file with navigation data for each averaged ensembles. The format of this file as the same as the output from getnav. Possible sub-options are:

file: file

Name of file in which navigation data should be written.

end

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

conversion_controls:

This option controls how data is converted. The following sub-options are available:

bin_mapping

Select this option to perform mapping of bin depths using pitch and roll data.

echo_scale_temp: float

Water temperature for scaling of echo amplitude data, in degree Celsius. Default is 10.0.

sound_speed: float

Speed of sound in water in m/s. Default is 1536. Here, it is probably best to specify the value used during collection of data. Correction for each specific ensemble is carried out during the calibration procedure with CTD data.

sound_absorption: float

Sound absorption for mapping echo amplitude data to their corresponding depths, in dB/m. Default is 0.039.

end

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

transducer_settings:

This option allows to specify transducer parameters. The following sub-options are available:

beam_angle= float

Angle in degree of beams relative to the vertical axis. This is usually 30.0 or 20.0. Default is 30.0.

beam_3_offset: float

Normally, the transducer is mounted so that beam numbered 3 faces the bow of the ship. However, this is often not the case. This option specifies this mounting offset in degree with increasing positive values corresponding to an offset toward starboard. Default is 0.0. Note that this parameter is not meant for the transducer misalignment.

transducer_depth: float

Depth of transducer in m. Default is 0.0. This option is required to get the true bin depths.

transducer_frequency: float

Transducer frequency in Hz. Since most NB VM-ADCP are operating on a frequency of 150kHz, the default is 153600.0.

transducer_misalignment:

This options allow to specify transducer misalignment relative to the selected value of parameter beam_3_offset. The following tilt values (in degree, default is 0.0) can be specified:

heading= float

pitch= float

roll= float

end

This keyword is mandatory and terminates the list of misalignment specifications.

bt_profiling_pings: integer

This option specifies the number of water tracking pings per water tracking pings. This parameter has no effect on data processing, however it is that value that will be loaded into the database, as the format of raw files does not contain this information. Furthermore, it has no effect on later processing of bottom track velocities.

end

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

processing_controls:

This option allows to tune the averaging and processing of raw ADCP pings. The following sub-options are available:

beam_solutions:

Specify the allowed beam solutions. With a well working transducer, one has four beam velocities to resolve current into Earth's coordinate system and an error velocity. With three beam velocities, only currents can be determined, one of them being probably less precise. When only two beam velocities are available, it still possible if available beams are orthogonal to each other, both of them being less precise. Clearly, when only one beam velocity is available for a direction, the current does not correspond to the vector average of velocities, yielding less precise data.

Before resolving currents, data are checked for bad values according to different methods. The latter determine how many beam velocities are made available for yielding currents. The following methods are implemented:

1

Set to bad beam values that already set to bad the ADCP.

2

Calculate the mean of the four beam values (those that have not been already set to bad by the ADCP), as well as the standard deviation. Beam values that lie outside the interval defined by the mean value and the standard deviation are set to bad.

The following list describes how the different variables are flagged as bad:

beam velocities

Method 1.

echo amplitude

Method 2.

spectral width

Method 2 on echo amplitude data.

bottom tracking velocities

Method 1.

In addition, the following sub-options are available:

min_beam= integer

The minimal beam solution allowed. This is a number between 2 and 4.

max_beam= integer

The maximal beam solution allowed. This is a number between 2 and 4.

end

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

The default for allowed beam solutions is to try all of them, starting from the best which is four. Results from a two beam solution are not expected to be of good quality. Hence, one should probably allow three and four beam solutions only. However, situation where the transducer was not well working might require a two beam solution.

time_controls:

This option allows to control the averaging process over time. The following parameters can be modified:

max_gap= integer

Maximal time gap allowed (in second) between two pings. If this value is exceeded, averaging of the current ensemble is stopped and averaging of a new one is started. Gaps between pings can also occur when navigation data is not available during a laps of time. The current ensemble is considered or thrown away according to the value of parameter avg_min (see below). Default is 20% of the given averaging interval.

avg_min= integer

Minimal average time (in second) allowed for an ensemble to be considered. This parameter is useful to decide whether the last ensemble should be kept or not. It is also used during the averaging process when large time gaps occur between valid pings (see parameter max_gap). Default value is 80% of the given averaging interval.

end

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

new_block

Normally, averaged ensembles are loaded into the database as successive profiles within the current block. A new block is only created for the first ensemble and when the number of profiles in the current block exceeds the allowed maximal value. This option allows a better control. If specified, a new block will also be created at the beginning of each time range specified at the end of the control file.

end

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

end

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

5. TIME RANGES

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

6. OUTPUT FILES

The following files are generated:

*.blk

Database files.

log_file

This file contains log information about the whole process, as well as some data in form of an ASCII table. Text information is commented with a %, so that this file can be read by the Matlab script process.m to view these data.

nav_output file

This file contains navigation data for each loaded ensemble. It has the same format as the output of getnav.

7. AUTHOR

Pierre Jaccard, Geophysical Institute, University of Bergen, 1999

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