mbm_bprSection: MB-System 5.0 (1)
Updated: 19 March 2012
NAMEmbm_bpr - MB-System macro to process data from a Seabird SBE53 pressure sensor into a tidal model for use by mbprocess.
SYNOPSISmbm_bpr -Ibprfile -Otidefile [-Doffset Rlon/lat -T -H -V]
DESCRIPTIONmbm_bpr is a perl shellscript used to translate pressure data from a Seabird SBE53 pressure sensor used as a Bottom Pressure Recorder (BPR) into tidal data that can be used to correct swath bathymetry data. The user specifies an input BPR data file in the *.tid format produced by Seabird software and the output path for the resulting tidefile.
By default, the output tidefile will be in the form of a text file with two columns:
Here time_d are time values in decimal epoch seconds (seconds since 1970 Jan 1 00:00:00) and the tide values are in meters. In this case, the tidefile is in format 1 as supported by mbprocess, so to make use of this tide data to correct swath bathymetry, use mbset as follows:
mbset -Idatalist.mb-1 -PTIDEFILE:tidefilename -PTIDEFORMAT:1
where datalist.mb-1 is the datalist referring to the data files to be processed. After using mbset to turn on tide correction, run mbprocess:
If the -T option is specified, then the output file will have the form of:
year month day hour min sec tide
In this case, the tidefile is in format 2 as supported by mbprocess, so to make use of this tide data to correct swath bathymetry, use mbset as follows:
mbset -Idatalist.mb-1 -PTIDEFILE:tidefilename -PTIDEFORMAT:2
where datalist.mb-1 is the datalist referring to the data files to be processed. After using mbset to turn on tide correction, run mbprocess.
The macro mbm_bpr calculates depth from pressure and latitude using the empirical formula for seawater in:
N. P. Fofonoff and R. C. Millard, Jr., ÔÔAlgorithms for computation of fundamental
properties of seawater,ÕÕ Unesco Tech. Papers in Mar. Sci., No. 44 1983.
and then calculates tidal data as the difference between the observed depth and a vertical reference depth. If a location is supplied using the -R option, mbm_bpr uses the latitude in the depth calculation and also extracts a tidal model corresponding the to BPR deployment site and timespan using the program mbotps. The vertical reference is then the average difference between the tidal model and the observed depths. If the user does not supply a location using the -R option, a location on the equator is assumed for the depth calculation and the vertical reference is the mean depth of the middle half of the depth time series (i.e. depths from 1/4 to 3/4 of the total time span). The user can specify an additional offset to apply to the tide data using the -Doffset option.
If the -T option is not used, then mbm_bpr will also output a shellscript that will, if executed, generate a GMT postscript plot of the tide data output. If a location has been specified so that a tidal model was also generated, the model will be plotted with the tide data.
AUTHORSHIPDavid W. Caress (email@example.com)
Monterey Bay Aquarium Research Institute
Dale N. Chayes (firstname.lastname@example.org)
Lamont-Doherty Earth Observatory
Suzanne H. O'Hara (email@example.com)
Lamont-Doherty Earth Observatory
To extract a tidal model, use mbm_bpr as follows:
mbm_bpr -I BPR.tid -OBPR.tde -R-110.682037/27.453160 -V
The output to the shell looks like:
1771 pressure values read from BPR.tid
Vertical reference to tidal model for position -110.682037 27.453160
Tide will be output as <time_d tide> values
A plot will be generated
Executing: mbotps -A1 -D1200 -R-110.682037/27.453160 -B2012/03/14/16/52/21 -E2012/03/15/22/22/21 -OBPR.tid_tidemodel.txt
Results are really in BPR.tid_tidemodel.txt
1690 pressure values output to BPR.tde
Vertical reference: 1267.31678290355 m
Executing mbm_xyplot -R1331743941.000000/1331850141.000000/-0.5071/0.5071 -IW0/0/0:BPR.tde -IW255/0/0:BPR.tid_tidemodel.txt -OBPR.tde_tideplot -L"Tide Data from BPR <BPR.tde> (black) & Tide Model (red):Seconds:Tide (meters)" -V
Executing <BPR.tde_tideplot.cmd> also invokes gv to view the plot on the screen.
The output tidal data file BPR.tde has the form:
where the first column is time in seconds since January 1, 1970 (epoch seconds, aka unix seconds, aka time_d values within MB-System), and the second column is the tidal signal in meters. In this case the reference tidal model is provided by mbotps, and the plot created by running the output shellscript BPR.tde_tideplot.cmd plots both the tidal data calculated by mbm_bpr and the tidal model extracted using mbotps.
Last Updated: 19 March 2012
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