MB-System Unix Manual Page: mbrolltimelag

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    mbrolltimelag
    Section:  MB-System 5.0  (1)
    Updated:  26 October 2009
    Index

    NAME

    mbrolltimelag - Calculates cross correlation between the apparent
    bottom slope in swath bathymetry data and the roll time series used by
    the sonar in order to assess attitude time lag problems.

    VERSION

    Version 5.0

    SYNOPSIS

    mbrolltimelag -Iswathdata [-Fformat
    -Nnping -Ooutroot -Snavchannel
    -Tnlag/lagmin/lagmax -V -H ]

    DESCRIPTION

    MBrolltimelag is an utility used to assess relative time errors,
    or time lag, between the ping timestamps of swath bathymetry data
    and the sonar attitude (roll and pitch) used in calculating
    the bathymetry. For any sonar ping, a roll error will cause
    the acrosstrack bathymetry profile to rotate vertically so that
    it is too shallow on one side of the swath and too deep on the other.
    Consequently, if no correction is made for the roll of the sonar, then the
    bathymetry data will appear to be ruffled in the outer swath.
    If the timestamps of the roll and ping data are consistent, then
    correcting for roll will produce bathymetry without these pronounced
    across-track artifacts. If, however, there is a lag between the two
    sets of time stamps, then the roll values used for correction will
    be incorrect, and the ruffles will still occur.

    In order to determine the amount of time lag, if any, associated
    with a swath bathymetry dataset, this program calculates the
    cross correlation between the roll signal and the apparent bottom
    slope in the case of no roll correction (in practice this latter
    value is found by subtracting the applied roll value from the
    apparent acrosstrack bottom slope). If the seafloor is planar so
    that the apparent slope signal is dominated by roll error, then
    there will be a distinct peak in the cross correlation function
    at the actual time lag.

    MBrolltimelag reads one or more swath sonar data files
    containing bathymetry data and calculates many cross correlation
    functions. The number of pings used for each calculation is
    specified with the -Nnping option. The range of time
    lags used and the number of lag values are all specified using
    the -Tnlag/lagmin/lagmax option. The cross correlation
    functions are output to a file named "swathdata_xcorr.txt", where
    swathdata is the input file or datalist specified with the
    -Iswathdata option. The macro mbm_xyplot is also
    called to generate a plot shellscript that, if run, will generate
    a postscript plot of the correlation functions.

    AUTHORSHIP

    David W. Caress (caress@mbari.org)

      Monterey Bay Aquarium Research Institute

    Dale N. Chayes (dale@ldeo.columbia.edu)

      Lamont-Doherty Earth Observatory

    OPTIONS

    -F

    format

    Sets the MBIO integer format identifier
    for the input file specified with the
    -I option. By default, mbrolltimelag
    infers the format from the "*.mbXX" MB-System suffix
    convention.
    -H

    This "help" flag cause the program to print out a description
    of its operation and then exit immediately.
    -I

    filename

    Sets the input filename. If format > 0 (set with the
    -F option) then the swath sonar data contained in infile
    is read and processed. If format < 0, then infile
    is assumed to be an ascii file containing a list of the input swath sonar
    data files to be processed and their formats.  The program will read
    and process the data in each one of these files. Each input file will
    have an associated output file with either the ".sga" or ".aga" suffix.
    In the infile file, each
    data file should be followed by a data format identifier, e.g.:

            datafile1 11

            datafile2 24

    This program uses the MBIO library and will read any swath sonar
    format supported by MBIO. A list of the swath sonar data formats
    currently supported by MBIO and their identifier values
    is given in the MBIO manual page. Default: infile = "datalist.mb-1".
    -N

    nping

    Sets the number of pings to be read for each cross correlation calculation.
    Default: lonflip = 0.
    -O

    outroot

    Sets the root of the output filenames.
    Default: output root is is the input filename minus any MB-System
    filename suffixe (e.g. the root derived from "datalistp.mb-1" will be
    "datalist").
    -S

    navchannel

    Sets MBrolltimelag to read the roll data from navigation records rather
    than the record type listed as the "navigation source" for a particular
    data format. Swath data formats may contain synchronous navigation
    (navigation is included in survey data records), asynchronous navigation
    (navigation comes in records separate from and at different times
    than the survey data records), or both (survey records contain merged
    navigation while the original asynchronous navigation is preserved in
    separate navigation records). Some data formats provide for multiple
    navigation sources, so that there are more than one channel of
    asynchronous data records. In this case one channel is always designated
    as the primary or active navigation channel. The -S option allows
    the user to specify that MBrolltimelag uses roll from
    the primary asynchronous navigation (-N0) or from one
    of three auxilliary navigation channels
    (-N1, -N2, or -N3). If -N is
    used but the data file
    does not contain asynchronous navigation or the specified auxilliary
    navigation channels, then mbnavlist will output nothing. To
    determine if a datafile contains asynchronous navigation and/or auxilliary
    navigation, run mbinfo using its -N option to get counts
    of all data record types in the file.
    Default: navchannel = 1.
    -T

    nlag/lagmin/lagmax

    Sets the time lag values used for the cross correlation calculations. A total
    of nlag  cross correlation values will be calculated evenly spaced from
    lagmin seconds to lagmax seconds.
    Default: nlag = 41, lagmin = -2.0 seconds, lagmax = 2.0 seconds.
    -V

    The -V option causes the program to be verbose.

    EXAMPLE

    Suppose you want to evaluate the possible roll time lag in a collection
    of Reson 7125 files referenced by a datalist called datalistp.mb-1. The
    sonar was pinging at 2Hz (twice a second), and roll is available at 10 Hz
    in asynchronous navigation records that can be accessed with
    navchannel = 2. We choose to calculate the cross correlation with
    time lags separated by 0.1 seconds from -2.0 to 2.0 seconds. The following
    will suffice:

            mbrolltimelag -Idatalistp.mb-1 -N41/-2.0/2.0 -S2 -V

    SEE ALSO

    mbsystem(l)

    BUGS

    Da.

     Index

    NAME
    VERSION
    SYNOPSIS
    DESCRIPTION
    AUTHORSHIP
    OPTIONS
    EXAMPLE
    SEE ALSO
    BUGS

Last Updated: 26 October 2009

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