MB-System Unix Manual Page
Section: MB-System 5.0 (1)
Updated: 10 November 2011
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.
mbrolltimelag -Iswathdata [-Fformat
-Krollsource -Nnping -Ooutroot -Snavchannel
-Tnlag/lagmin/lagmax -V -H ]
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.
David W. Caress (email@example.com)
Monterey Bay Aquarium Research Institute
Dale N. Chayes (firstname.lastname@example.org)
Lamont-Doherty Earth Observatory
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
This "help" flag cause the program to print out a description
of its operation and then exit immediately.
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.:
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".
This option sets the type of data record from which the roll values
will be extracted. By default, the roll values are extracted from
survey data records. If the -S option is used, the roll data
will be extracted from primary or ancilliary navigation records. If
this -K option is set, then the roll data will be extracted from
data records of type Krollsource, where the possible values are listed
MB_DATA_DATA 1 /* general survey data */
MB_DATA_CALIBRATE 4 /* Hydrosweep DS */
MB_DATA_MEAN_VELOCITY 5 /* Hydrosweep DS */
MB_DATA_VELOCITY_PROFILE 6 /* general */
MB_DATA_NAV 12 /* Simrad, Reson 7k */
MB_DATA_HEADING 17 /* Simrad, Hypack */
MB_DATA_ATTITUDE 18 /* Simrad, Hypack, Reson 7k */
MB_DATA_SSV 19 /* Simrad */
MB_DATA_NAV1 28 /* ancillary nav system 1 */
MB_DATA_NAV2 29 /* ancillary nav system 2 */
MB_DATA_NAV3 30 /* ancillary nav system 3 */
MB_DATA_MOTION 32 /* Reson 7k */
MB_DATA_SIDESCAN2 37 /* Reson 7k, XTF */
MB_DATA_SIDESCAN3 38 /* Reson 7k, XTF */
MB_DATA_ROLL 40 /* Reson 7k */
MB_DATA_PITCH 41 /* Reson 7k */
MB_DATA_NMEA_RMC 48 /* NMEA */
MB_DATA_NMEA_DBT 49 /* NMEA */
MB_DATA_NMEA_DPT 50 /* NMEA */
MB_DATA_NMEA_ZDA 51 /* NMEA */
MB_DATA_NMEA_GLL 52 /* NMEA */
MB_DATA_NMEA_GGA 53 /* NMEA */
MB_DATA_ATTITUDE1 55 /* ancillary attitude system 1 */
MB_DATA_ATTITUDE2 56 /* ancillary attitude system 2 */
MB_DATA_ATTITUDE3 57 /* ancillary attitude system 3 */
A typical value is Krollsource=18, which specifies extraction of roll from asynchronous attitude
data records. This option supercedes the -S option.
Sets the number of pings to be read for each cross correlation calculation.
Default: nping = 50.
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
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.
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.
The -V option causes the program to be verbose.
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
mbrolltimelag -Idatalistp.mb-1 -N41/-2.0/2.0 -S2 -V
- SEE ALSO
Last Updated: 10 November 2011
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