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<title>MGD77SNIFFER</title>
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<h1 align=center>MGD77SNIFFER</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#REQUIREMENTS">REQUIREMENTS</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#MGD77 FIELD INFO">MGD77 FIELD INFO</a><br>
<a href="#GRID FILE INFO">GRID FILE INFO</a><br>
<a href="#E77 ERROR FORMAT">E77 ERROR FORMAT</a><br>
<a href="#EXAMPLES">EXAMPLES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#REFERENCES">REFERENCES</a><br>
<hr>
<a name="NAME"></a>
<h2>NAME</h2>
<p style="margin-left:11%; margin-top: 1em">mgd77sniffer
− Scan for errors in MGD77 data</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77sniffer</b>
<i>NGDC-ids</i> [
<b>−A</b><i>fieldabbrev</i>,<i>scale</i>,<i>offset</i>
] [ <b>−C</b><i>maxspd</i> ] [
<b>−Dd</b>|<b>e</b>|<b>E</b>|<b>f</b>|<b>l</b>|<b>m</b>|<b>s</b>|<b>v</b>
][<i>r</i>] [
<b>−g</b><i>fieldabbrev</i>,<i>imggrid</i>,<i>scale</i>,<i>mode</i>
] [ <b>−G</b><i>fieldabbrev</i>,<i>grid</i> ] [
<b>−H</b>[<b>i</b>][<i>nrec</i>] ] [
<b>−I</b><i>fieldabbrev</i>,<i>rec1</i>,<i>recN</i> ]
[ <b>−K</b> ] [ <b>−L</b><i>custom limits
file</i> ] [ <b>−N</b> ] [
<b>−Q</b>[<b>b</b>|<b>c</b>|<b>l</b>|<b>n</b>][[<b>/</b>]<i>threshold</i>]
] [
<b>−R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>]
] [ <b>−Sd</b>|<b>s</b>|<b>t</b> ] [
<b>−T</b><i>gap</i> ] [ <b>−V</b> ] [
<b>−Wc</b>|<b>g</b>|<b>o</b>|<b>s</b>|<b>t</b>|<b>v</b>|<b>x</b>
] [
<b>−bo</b>[<b>s</b>|<b>S</b>|<b>d</b>|<b>D</b>[<i>ncol</i>]|<b>c</b>[<i>var1</i><b>/</b><i>...</i>]]
]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77sniffer</b>
scans old (pre-Y2K) and new format ASCII MGD77 files for
errors using point-by-point sanity checking, along-track
detection of excessive slopes, and optional comparison of
cruise data with global gravity and predicted bathymetry
grids. Detected data problems are output by default as
verbose descriptions of each detected error, often resulting
in multiple messages per scanned record. Data problems are
optionally output (<b>−De</b> option) using a
computer-parseable format (see E77 ERROR FORMAT description
below). Default error thresholds are derived from histograms
of all MGD77 geophysical data collected between 1952 and
January, 2006. Thresholds are adjustable with the
<b>−L</b> option. <i><br>
NGDC-ids</i></p>
<p style="margin-left:22%;">Can be one or more of five
kinds of specifiers: <br>
1) 8-character NGDC IDs, e.g., 01010083, JA010010etc., etc.
<br>
2) 2-character <agency> codes which will return all
cruises from each agency. <br>
3) 4-character <agency><vessel> codes, which
will return all cruises from those vessels. <br>
4) =<list>, where <list> is a table with NGDC
IDs, one per line. <br>
5) If nothing is specified we return all cruises in the data
base. <br>
(See mgd77info <b>−L</b> for agency and vessel codes).
The ".mgd77" or ".nc" extensions will
automatically be appended, if needed (use <b>−I</b> to
ignore certain file types). Cruise files will be looked for
first in the current directory and second in all directories
listed in <b>$MGD77_HOME</b>/mgd77_paths.txt [If
<b>$MGD77_HOME</b> is not set it will default to
<b>$GMT_SHAREDIR</b>/mgd77].</p>
<a name="REQUIREMENTS"></a>
<h2>REQUIREMENTS</h2>
<p style="margin-left:11%; margin-top: 1em">The
mgd77sniffer links with Generic Mapping Tools 4.0 or later
along with the supplemental GMT packages x2sys and mgd77.
See http://gmt.soest.hawaii.edu for GMT details. Grids for
comparison with cruise data may be downloaded via the
web.</p>
<a name="OPTIONS"></a>
<h2>OPTIONS</h2>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−A</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Apply scale factor
and DC adjustment to specified data field. Allows adjustment
of cruise data prior to along-track analysis. CAUTION: data
must be thoroughly examined before applying these global
data adjustments. May not be used for multiple cruises.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−C</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Set maximum ship
speed in m/s, or knots with <b>−N</b> option. Ship
speeds exceeding 10 m/s (~20 knots) are flagged as excessive
by default.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−D</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Suppress default
warning output and only dump cruise data row-by-row such as
values, gradients, grid-cruise differences, E77 error
summaries for each record, re-created MGD77 records or
sniffer limits. Append r to include all records (default
omits records where navigation errors were detected).</p></td>
</table>
<p style="margin-left:22%; margin-top: 1em"><b>−Dd</b>
output differences between cruise and grid data. Requires
<b>−G</b> option. Output columns include:</p>
<p style="margin-left:22%; margin-top: 1em"><i>lat lon dist
cruiseZ gridZ diff [cruiseZ2 gridZ2 diff2 ...]</i></p>
<p style="margin-left:22%; margin-top: 1em">Note: grid
values are subtracted from cruise data so a positive
difference implies cruise > grid. For multiple grid
comparison, <i>cruiseZ gridZ diff</i> are repeated for each
grid comparison in command line order.</p>
<p style="margin-left:22%; margin-top: 1em"><b>−De</b>
output E77 error classification format. Error output is
divided into (1) a header containing information globally
applicable to the cruise and (2) individual error records
summarizing all errors encountered in each cruise record.
mgd77sniffer writes E77 directly to <ngdc_id.e77> file
handle. See <b>E77 ERROR FORMAT</b> below for additional
details.</p>
<p style="margin-left:22%; margin-top: 1em"><b>−DE</b>
Same as <b>−De</b> but no regression tests will be
carried out.</p>
<p style="margin-left:22%; margin-top: 1em"><b>−Df</b>
output delta Z (change in geophysical field) column and
delta S (change in distance) for each geophysical field.
Distance between observations often differ for different
fields depending on instrument sampling rate, so ds is
included for each geophysical observation. Output columns
include:</p>
<p style="margin-left:22%; margin-top: 1em"><i>d[twt] ds
d[depth] ds d[mtf1] ds d[mtf2] ds d[mag] ds d[diur] ds
d[msd] ds d[gobs] ds d[eot] ds d[faa] ds</i></p>
<p style="margin-left:22%; margin-top: 1em"><b>−Dl</b>
display mgd77sniffer limits. Customize this output to create
a custom limits file for the <b>−L</b> option. No
additional arguments are required. Output columns
include:</p>
<p style="margin-left:22%; margin-top: 1em"><i>fieldabbrev
min max maxSlope maxArea</i></p>
<p style="margin-left:22%; margin-top: 1em"><b>−Dm</b>
output MGD77 format records in Y2K-compliant MGD77
format</p>
<p style="margin-left:22%; margin-top: 1em"><b>−Dn</b>
output distance to coast for each record. Requires
<b>−Gnav</b> or <b>−gnav</b> option. Output
columns include:</p>
<p style="margin-left:22%; margin-top: 1em"><i>lat lon dist
distToCoast</i></p>
<p style="margin-left:22%; margin-top: 1em"><b>−Ds</b>
output calculated gradients for speed and geophysical
fields. Gradients correspond to the gradient type selected
in the <b>−S</b> option (spatial derivatives by
default). Output columns include:</p>
<p style="margin-left:22%; margin-top: 1em"><i>speed d[twt]
d[depth] d[mtf1] d[mtf2] d[mag] d[diur] d[msd] d[gobs]
d[eot] d[faa]</i></p>
<p style="margin-left:22%; margin-top: 1em">See <b>MGD77
FIELD INFO</b> below for field and abbreviations
descriptions.</p>
<p style="margin-left:22%; margin-top: 1em"><b>−Dv</b>
display values for the twelve position and geophysical
fields for each MGD77 data record (in this order):</p>
<p style="margin-left:22%; margin-top: 1em"><i>lat lon twt
depth mtf1 mtf2 mag diur msens gobs eot faa</i></p>
<p style="margin-left:22%; margin-top: 1em">See below for
<b>MGD77 FIELD INFO</b>.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−g</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Compare cruise data
to the specified grid in Sandwell/Smith Mercator format.
Requires a valid MGD77 field abbreviation (see <b>MGD77
FIELD INFO</b> below) followed by a comma, the path (if not
in current directory) and grid filename, a scale to multiply
the data (1 or 0.1), and mode which stand for the following:
(0) Img files with no constraint code, returns data at all
points, (1) Img file with constraints coded, return data at
all points, (2) Img file with constraints coded, return data
only at constrained points and NaN elsewhere, and (3) Img
file with constraints coded, return 1 at constraints and 0
elsewhere.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−G</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Compare cruise data
to the specified grid. Requires a valid MGD77 field
abbreviation (see <b>MGD77 FIELD INFO</b> below) followed by
a comma, then the path (if not in current directory) and
grid filename. Multiple grid comparison is supported by
using separate <b>−g</b> or <b>−G</b> calls for
each grid. See <b>GRID FILE INFO</b> below.</p></td>
</table>
<p style="margin-left:22%; margin-top: 1em">Grid comparison
activates several additional error checks. (1) Re-weighted
Least Squares Regression of ship versus grid data determines
slope and DC shift, which when differing from expected 1 and
0, respectively, may indicate incorrectly scaled ship data,
including incorrect units or instrument drift as well as
erroneous gravity tie-in. (2) Accumulated ship grid offsets
are computed along-track and excessive offsets are flagged
according to <i>maxArea</i> threshold (use <b>−L</b>
option to adjust <i>maxArea</i>). Warning: predicted
bathymetry grids are constrained by cruise data so grids and
cruise data are not always independent. Comparison of cruise
bathymetry with predicted bathymetry grids also activates a
"navigation crossing over land" check.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−H</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">(with
<b>−G</b>|<b>g</b> only) disable (or force) decimation
during RLS analysis of ship and gridded data. By default
mgd77sniffer analyses both the full and decimated data sets
then reports RLS statistics for the higher correlation
regression.</p> </td>
</table>
<p style="margin-left:22%; margin-top: 1em"><b>−Hb</b>
analyze both (default), report better of two.</p>
<p style="margin-left:22%; margin-top: 1em"><b>−Hd</b>
to disable data decimation (equivalent to -H with no
argument).</p>
<p style="margin-left:22%; margin-top: 1em"><b>−Hf</b>
to force data decimation.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−I</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Append a field
abbreviation and the first and last record in a range of
records that should be flagged as bad (and set to NaN prior
to the analysis). Repeat as many times as needed. May not be
used for multiple cruises.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−K</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Reverse navigation
quality flags (good to bad and vice versa). May be necessary
when a majority of navigation fixes are erroneously flagged
bad, which can happen when a cruise’s first navigation
fix is extremely erroneous. Caution! This will affect
sniffer output and should only be attempted after careful
manual navigation review.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−L</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Override
mgd77sniffer default error detection limits. Supply path and
filename to the custom limits file. Rows not beginning with
a valid MGD77 field abbreviation are ignored. Field
abbreviations are listed below in exact form under MGD77
FIELD INFO. Multiple field limits may be modified using one
default file, one field per line. Field min, max, max slope
and max area may be changed for each field. Max slope
pertains to the gradient type selected using the
<b>−S</b> option. Max area is used by the
<b>−G</b> option as the threshold for flagging
excessive offsets from the specified grid. Dump defaults
<b>−Dl</b> to view syntax or to quickly create an
editable custom limits file.</p></td>
</table>
<p style="margin-left:22%; margin-top: 1em">Example custom
default file contents (see below for units): <br>
# abbrev min max maxSlope maxArea <br>
twt 0 15 1 0 <br>
depth 0 11000 500 5000 <br>
mag -800 800 - - <br>
faa -300 300 100 2500</p>
<p style="margin-left:22%; margin-top: 1em">Use a dash
’-’ to retain a default limit. Hint: to test
your custom limits, try: mgd77sniffer <b>−Dl
−L</b><yourlimitsfile></p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−N</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Use nautical
units.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−P</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Flag regression
statistics that are outside the specified confidence level.
(i.e., -P5 flags coefficients m, b, rms, and r that fall
outside 95%.)</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−Q</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Quick mode, use
bilinear rather than bicubic interpolation [Default].
Alternatively, select the interpolation mode by adding
<b>b</b> for B-spline smoothing, <b>c</b> for bicubic
interpolation, <b>l</b> for bilinear interpolation or
<b>n</b> for nearest-neighbor value. Optionally, append
<i>threshold</i> in the range [0,1]. This parameter controls
how close to nodes with NaN values the interpolation will
go. E.g., a <i>threshold</i> of 0.5 will interpolate about
half way from a non-NaN to a NaN node, whereas 0.1 will go
about 90% of the way, etc. [Default is 1, which means none
of the (4 or 16) nearby nodes may be NaN]. <b>−Q0</b>
will just return the value of the nearest node instead of
interpolating. This is the same as using
<b>−Qn</b>.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−R</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top"><i>west, east,
south,</i> and <i>north</i> specify the Region of interest,
and you may specify them in decimal degrees or in
[+-]dd:mm[:ss.xxx][W|E|S|N] format. Append <b>r</b> if lower
left and upper right map coordinates are given instead of
w/e/s/n. The two shorthands <b>−Rg</b> and
<b>−Rd</b> stand for global domain (0/360 and
-180/+180 in longitude respectively, with -90/+90 in
latitude). Alternatively, specify the name of an existing
grid file and the <b>−R</b> settings (and grid
spacing, if applicable) are copied from the grid.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−S</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Specify gradient
type for along-track excessive slope checking.</p></td>
</table>
<p style="margin-left:22%;"><b>−Sd</b> Calculate
change in z values along track (dz). Output is given in
geophysical units, e.g. mGal. <b><br>
−Ss</b> Calculate spatial gradients (dz/ds). Output is
given in geophysical units per km along the survey track,
e.g. mGal/km. <b><br>
−St</b> Calculate time gradients (dz/dt) [default].
Output is given in geophysical units per second along the
survey track, e.g. mGal/sec.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−T</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Adjusts
mgd77sniffer gap handling. By default, data gaps greater
than 5 km are skipped. Set to zero to de-activate gap
skipping.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−W</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Print out only
certain warning types for verbose error messages. Comma
delimit any combination of <b>c|g|o|s|t|v|x</b>: where
(<b>c</b>) type code warnings, (<b>g</b>)radient out of
range, (<b>o</b>)ffsets from grid (requires
<b>−G</b>|<b>g</b>), (<b>s</b>)peed out of range,
(<b>t</b>)ime warnings, (<b>v</b>)alue out of range,
(<b>x</b>) warning summaries. By default ALL warning
messages are printed.Not compatible with any <b>−D</b>
options.</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−V</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects verbose
mode, which will send progress reports to stderr [Default
runs "silently"].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−b</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">output binary data
for <b>−D</b>d|f|s|v option. Append <b>s</b> for
single and <b>d for double precision [Default is
double].</b></p> </td>
</table>
<a name="MGD77 FIELD INFO"></a>
<h2>MGD77 FIELD INFO</h2>
<p style="margin-left:11%; margin-top: 1em"><i>Field
Abbreviation Units</i> <br>
Two-way Travel Time twt sec <br>
Corrected Depth depth m <br>
Mag Total Field1 mtf1 nT <br>
Mag Total Field2 mtf2 nT <br>
Residual Magnetic mag nT <br>
Diurnal Correction diur nT <br>
Mag Sensor Depth/Alt msens m <br>
Observed Gravity gobs mGal <br>
Eotvos Correction eot mGal <br>
Free Air Anomaly faa mGal</p>
<a name="GRID FILE INFO"></a>
<h2>GRID FILE INFO</h2>
<p style="margin-left:11%; margin-top: 1em">For
<b>−g</b> the grids must be in the format used by
Sandwell & Smith, which is a spherical Mercator 2-byte
grid with no header. For <b>−G</b> the grid files can
be of any grid type supported by GMT and therefore must
contain a GMT header. A correctly formatted *.i2 grid file
can be generated using grdraster as shown below.</p>
<p style="margin-left:11%; margin-top: 1em">gmtset
GRIDFILE_SHORTHAND TRUE</p>
<p style="margin-left:11%; margin-top: 1em">Create/edit
.gmt_io file to include the following rows: <br>
# GMT I/O shorthand file <br>
# suffix format_id scale offset NaN <br>
grd 0 - - - <br>
i2 2 - - 32767</p>
<p style="margin-left:11%; margin-top: 1em">grdraster 1
-R0/359:55/-90/90 -Getopo5_hdr.i2</p>
<p style="margin-left:11%; margin-top: 1em">The new grid,
etopo5_hdr.i2 in this example, contains a GMT header and can
be used in the <b>−G</b> option to compare cruise
depth with grid values.</p>
<a name="E77 ERROR FORMAT"></a>
<h2>E77 ERROR FORMAT</h2>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em" valign="top"><b>Header</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Information
pertaining to an entire cruise, such as NGDC and survey
institution identification codes, cruise examination time,
two-way travel time corrector information, data precision
warnings, as well as systematic scales, DC shifts and
correlation coefficients from global grid comparisons are
reported as E77 header information.</p></td>
</table>
<p style="margin-left:22%; margin-top: 1em"><b>Sample</b>
<br>
# Cruise 08010039 ID 74010908 MGD77 FILE VERSION: 19801230
N_RECS: 3066 <br>
# Examined: Wed Oct 3 16:30:13 2007 by mtchandl <br>
# Arguments: -De -Gdepth,/data/GRIDS/etopo5_hdr.i2 <br>
N Errata table verification status <br>
# mgd77manage applies corrections if the errata table is
verified (toggle ’N’ above to ’Y’
after review) <br>
# For instructions on E77 format and usage, see
http://gmt.soest.hawaii.edu/mgd77/errata.php <br>
# Verified by: <br>
# Comments: <br>
# Errata: Header <br>
Y-E-08010039-H13-02: Invalid Magnetics Sampling Rate: (99) [
] <br>
Y-W-08010039-H13-10: Survey year (1975) outside magnetic
reference field IGRF 1965 time range (1965-1970) <br>
Y-I-08010039-depth-00: RLS m: 1.00053 b: 0 rms: 127.851 r:
0.973422 significant: 1 decimation: 0 <br>
Y-W-08010039-twt-09: More recent bathymetry correction table
available <br>
Y-W-08010039-mtf1-10: Integer precision <br>
Y-W-08010039-mag-10: Integer precision</p>
<p style="margin-left:11%;"><b>Error Record</b></p>
<p style="margin-left:22%;">Individual error records have
strict format. Included is a time or distance column
followed by record number, a formatted error code string,
and finally a verbose description of errors detected in the
record. Three error classes are encoded into the error code
string with different alphabetic characters representing
unique error types. See below for error code format
description.</p>
<p style="margin-left:22%; margin-top: 1em"><b>Format</b>
<br>
<time/distance> <record number> <error code
string> <description></p>
<p style="margin-left:22%; margin-top: 1em"><b>Sample</b>
<br>
# Errata: Data</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="22%"></td>
<td width="-4%"></td>
<td width="8%">
<p valign="top">Y</p></td>
<td width="8%"></td>
<td width="8%"></td>
<td width="30%"></td>
<td width="8%"></td>
<td width="8%"></td>
<td width="7%"></td>
<td width="5%">
</td>
<tr valign="top" align="left">
<td width="22%"></td>
<td width="-4%"></td>
<td width="8%">
<p valign="top">08010039</p></td>
<td width="8%"></td>
<td width="8%">
<p valign="top">1975-05-10T22:16:05.88</p></td>
<td width="30%"></td>
<td width="8%"></td>
<td width="8%">
<p valign="top">74</p></td>
<td width="7%"></td>
<td width="5%">
</td>
<tr valign="top" align="left">
<td width="22%"></td>
<td width="-4%"></td>
<td width="8%"></td>
<td width="8%"></td>
<td width="8%"></td>
<td width="30%"></td>
<td width="8%"></td>
<td width="8%">
<p valign="top">C-0-0</p></td>
<td width="7%"></td>
<td width="5%">
<p valign="top">NAV: excessive speed</p></td>
</table>
<p style="margin-left:11%;"><b>Error Code
Description</b></p>
<p style="margin-left:22%;">Each of the three error classes
is separated by a dash ’-’ and described by a
combination of alphabetic characters or 0 signifying no
detected problems.</p>
<p style="margin-left:22%; margin-top: 1em">Error classes:
NAV-VAL-GRAD</p>
<p style="margin-left:22%; margin-top: 1em"><b>Error Class
Descriptions</b> <br>
NAV (navigation): <br>
0 - fine <br>
A - time out of range <br>
B - time decreasing <br>
C - excessive speed <br>
D - above sea level <br>
E - lat undefined <br>
F - lon undefined</p>
<p style="margin-left:22%; margin-top: 1em">VAL (value):
<br>
0 - fine <br>
K - twt invalid <br>
L - depth invalid <br>
O - mtf1 invalid <br>
etc.</p>
<p style="margin-left:22%; margin-top: 1em">GRAD
(gradient): <br>
0 - fine <br>
K - d[twt] excessive <br>
L - d[depth] excessive <br>
O - d[mtf1] excessive <br>
etc.</p>
<p style="margin-left:22%; margin-top: 1em">The NAV error
class has unique cases while VAL and GRAD classes are
described by alphabetic characters for each of the 24
numeric fields in MGD77 format order.</p>
<p style="margin-left:22%; margin-top: 1em">MGD77
bit-pattern w/ E77 alpha characters <br>
|-------------------------------------------------|----------|
<br>
| X W V U T S R Q P O N M L K J I H G F E D C B A | E77 Code
| <br>
| - - - - - - - - - - - - - - - - - - - - - - - - | - - - -
-| <br>
| n f e g m d m m m m b b d t p l l m h d m y t d | F I |
<br>
| q a o o s i s a t t t c e w t o a i o a o e z r | i D |
<br>
| c a t b d u e g f f c c p t c n t n u y n a t | e | <br>
| s r n 2 1 t r t r | l | <br>
| s h h | d | <br>
| - - - - - - - - - - - - - - - - - - - - - - - - | - - - -
-| <br>
| 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 | Bit
place| <br>
| - G C G C C - G G G - - G G - - - T T T T T - - | Bit type
| <br>
|-------------------------------------------------|----------|
<br>
Bit types: (G)eophysical, (C)orrection, (T)ime</p>
<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
<p style="margin-left:11%; margin-top: 1em">To scan for
excessive values or gradients, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77sniffer</b>
08010001</p>
<p style="margin-left:11%; margin-top: 1em">To dump cruise
gradients, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77sniffer</b>
08010001 -Ds</p>
<p style="margin-left:11%; margin-top: 1em">To compare
cruise depth with ETOPO5 bathymetry and gravity with
Sandwell/Smith 2 min gravity version 11, try</p>
<p style="margin-left:11%; margin-top: 1em"><b>mgd77sniffer</b>
08010001 <b>−G</b>depth,/data/GRIDS/etopo5_hdr.i2
<b>−g</b>faa,/data/GRIDS/grav.11.2.img,0.1,1</p>
<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>
<p style="margin-left:11%; margin-top: 1em"><i><A HREF="mgd77list.html">mgd77list</A></i>(1),
<i><A HREF="mgd77track.html">mgd77track</A></i>(1) <i><A HREF="x2sys_init.html">x2sys_init</A></i>(1)</p>
<a name="REFERENCES"></a>
<h2>REFERENCES</h2>
<p style="margin-left:11%; margin-top: 1em">Wessel, P., and
W. H. F. Smith, 2009, The Generic Mapping Tools (GMT)
version 4.5.0 Technical Reference & Cookbook,
SOEST/NOAA. <br>
Wessel, P., and W. H. F. Smith, 1998, New, Improved Version
of Generic Mapping Tools Released, EOS Trans., AGU, 79 (47),
p. 579. <br>
Wessel, P., and W. H. F. Smith, 1995, New Version of the
Generic Mapping Tools Released, EOS Trans., AGU, 76 (33), p.
329. <br>
Wessel, P., and W. H. F. Smith, 1995, New Version of the
Generic Mapping Tools Released,
http://www.agu.org/eos_elec/95154e.html, Copyright 1995 by
the American Geophysical Union. <br>
Wessel, P., and W. H. F. Smith, 1991, Free Software Helps
Map and Display Data, EOS Trans., AGU, 72 (41), p. 441. <br>
The Marine Geophysical Data Exchange Format -
"MGD77", see
<i>http://www.ngdc.noaa.gov/mgg/dat/geodas/docs/mgd77.txt</i></p>
<hr>
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