PROCESS WBT, WBT2, WBT3  (water bottom time definition)
          ------- ---  ----  ----


Parameters, alphabetically:
day      guided    index     lprint    nscan     offset    pass
peak     prestk    seg       sel       sepp      ses       solrat
thres    track     vel

Documentation Date:  22 October 2014
Modifications:
    Oct. 14 - Honor SEGY Rev 1 deep water delay scalar (diskin).
    ???  - Honor SEGY Rev 1 water bottom depth scalar.
    15 July 14 - Add parameters GUIDED and SEG.
    7 June 11 - Honor PRESTK when using VEL.
    5 Nov. 09 - Add parameters PASS for offline filtering.
    22 Feb 2008 - Honor TRACK when doing VEL.

PROCESS WBT associates a water bottom time with every trace.  The time
is placed in the trace header and may be used by other processes
such as mute, nmo, or decon for 'hanging' windows from. 'Hanging'
windows means that the window times are added to the water bottom time,
thus the window times may be the same distance from the water bottom on
all traces.

PROCESSES WBT2 and WBT3 are identical to WBT and enable three unique
WBT processes to be given in a single SIOSEIS job.

The water bottom times may be entered in one of several ways:  
1) Listing rp-time pairs
2) Listing gmt time-time pairs
3) Converting depths to time using the SEG-Y source depth entry.
4) Automatic picking using a sliding average amplitude window.
5) Automatic picking using the first absolute value amplitude that
   exceeds a trhreshold.
6) Automatic picking using the largest positive/negative/absolute value
   of each trace.

The rp-time pairs method of entering the water bottom times
consists of entering a list of pairs of rp numbers followed by the two
way travel time for the rp.

The rp numbers must strictly increase.  Rp numbers may be assigned using
SIOSEIS processes geom or header.  The water bottom time specified will
be associated with all traces with the same rp number (a single cdp has
the same rp number!).  Water bottom times not specified are calculated
by interpolation or held constant.
*** NOTE ***
The only 'end' needed is the 'end' to terminate the wbt parameters when
using rp-time pairs or gmt-time pairs.

The gmt time method consists of specifying the Julian day via the
parameter 'day' and then a list of gmt time - water bottom time pairs.
The parameter 'day' must be given prior to the gmt time and must be 
given on the first pair.  Furthermore, the day must be given on day 
changes.  The gmt time is given in terms of decimal minutes of the 24
hour clock, thus 1532.75 represents 1532 and 45 seconds.  Water bottom
times not specified are calculated by interpolation or are held constant.  

Example 1:
     wbt
          41 1.197
          43 1.199
     end
RPS less than 41 will receive a water bottom time of 1.197, rp 41 a time
of 1.197, 42 a time of 1.198, 43 a time of 1.199, and rp's larger than
43 a time of 1.199. 

Example 2:
     wbt
     day 265 1045 .21
          1100 .25
          2200 2.0
     day 266 0300 3.5
     end


THE PARAMETER DICTIONARY
--- --------- ----------

PASS   - The passband of a 55 point time domain convolutional zero phase
         bandpass filter (same as process filter ftype 99) to apply 
         before picking.  The filtered data are NOT passed to the next
         seismic process, thus the filter is applied "offline".  The
         low and high "corners" of the filter must be given.  Offline
         filtering is available on all automatic picking options (thres,
         solrat, peak, short/long).
         Preset = none      e.g.  pass 100 200
         
LPRINT - Print switch.
       =2, The water bottom time for every trace is printed.
       =4, When using the SOLRAT method, the short and long averages
         are printed on EVERY trace.  THIS CAN CAUSE A LARGE VOLUME
         OF PRINT OUTPUT.
         Preset = 0     e.g.   lprint 4

INDEX  - The index within the SEG-Y trace header where the water
         bottom time will be written.  Time is the floating point
         number of seconds and is type REAL.
         Preset = 50    e.g.     index 59

Converting SEG-Y water bottom depth (word 16) to time:
---------- ----- ----- ------ ----- --------  -- -----
VEL    - The velocity to convert the water depth (SEGY long word 16
         with scalar in short word 16) to time.  Useful with SeaBeam
         and Knudsen data.
         Preset = 0     e.g.   vel 1450

TRACK  - The maximum deviation, in seconds, the water bottom time
         may have from the previous trace's water bottom time.  If the
         deviation exceeds TRACK, then the previous trace's water
         bottom time is used.  Done in time since most seismic plots
         are in time.
         Preset = 99.    e.g.  track .05

Listing rp-time pairs:
------- ------- ------
       - List of rp numbers and two way travel times.  The rp numbers
         must increase.
         Preset = 0     e.g.    41 1.197

Listing gmt-time pairs:
------- -------- ------
DAY    - The Julian day of the GMT-time pairs that follow.
       - List of gmt times and two way travel times.  The gmt times must
         increase unless the day parameter is used to set a new day.
         Preset = 0     e.g.    1100 .25

Automatic Pick Using Average Amplitude Windows:
--------- ---- ----- ------- --------- --------
    The water bottom time is picked when the ratio of a short sliding
average amplitude window over a long average amplitude window exceeds
the user given ratio.  The picked time is put in trace header word 50.

SOLRAT - Short Over Long window RATio.
         Preset = 0.     e.g.  solrat 1.5

SES    - Start and Stop times, in seconds, of the first Short window.
         The SES window should be prior to the water bottom, so that
         the first window  doesn't contain seismic data (lower
         amplitudes than the SEL window).
         Preset = 0      e.g.    ses 0 .1

SEL    - Start and Stop times, in seconds, of the Long window.  SEL
         should be below the anticipated water bottom, so that the
         window contains seismic data (higher amplitudes than the SES 
         window).
         Preset = 0      e.g.    sel 6 7

TRACK  - The maximum deviation, in seconds, the time of the pick
         may have from the previous good pick.  When the pick time is
         before the track, the pick is discarded and a the SES window
         is advanced one sample before trying again.  If the pick is
         greater than previous trace pick plus TRACK, the pick from
         the previous trace is used.
         Preset = 99.    e.g.  track .05

Automatic Pick Using First Amplitude Greater Than A Threshold.
--------- ---- ----- ----- --------- ------- ---- - ----------
    The water bottom time is picked when the first amplitude exceeds
a threshold.  The absolute value of the trace amplitude is compared
to the user given threshold.  

THRES  - The threshold (a value) which defines the water bottom.
         Usually the trace amplitudes in the water column are lower
         than the water bottom reflection by several orders of
         magnitude.  The trace is scanned from the first sample, so
         the direct arrival might exceed the threshold.  Process
         PROUT may be used to examine the trace amplitudes.
         Preset = 0     e.g. thres 16000

TRACK  - The maximum deviation, in seconds, the time of the pick
         may have from the previous good pick.  When the time is
         outside (previous pick time +/- track), the previous
         pick time is used.
         Preset = 99.    e.g.  track .05

Parameters used by autopickers SOLRAT and THRES and VEL
---------- ---- -- ----------- ------ --- ----- --- ---
PRESTK - A YES/NO switch when set to YES means that the data are rp
         sorted and that only the first trace of each rp should be
         picked and that the water bottom time/depth of the first
         trace within the rp should be used on all traces within
         the rp.  In this case, a new rp starts when the rp number
         (SEG-Y header word 6) changes.
         Preset = no      e.g.   prestk yes

Automatic Pick Using the Peak Amplitude:
--------- ---- ----- --- ---- --------- 
PEAK   - Invokes the "peak" picker which uses the time associated with
         the "largest" amplitude of each trace.
       =POS, Use the largest positive value of each trace.
       =NEG, Use the largest negative value of each trace.
       =ABS, Use the largest absolute value of each trace.
        Preset = none     e.g.   peak abs

SEPP   - Start and End time of the Peak Picker.  The window for
         PEAK to operate in.
         Preset = entire trace.

TRACK  - The maximum deviation, in seconds, the time of the pick
         may have from the previous good pick.  When the time is
         outside (previous pick time +/- track), the previous
         pick time is used.
         Preset = 99.    e.g.  track .05

Automatic peak/trough pick using a window based on the existing water bottom time.
--------- ----------- ---- ----- - ------ ----- -- --- -------- ----- ------ -----
(implemented in  SIOSEIS ver 2014.4.2 (11 Jul. 2014))

GUIDED - Invokes the "peak" picker which uses the time associated with
         the "largest" amplitude of each trace.
       =POS, Use the largest positive value of each trace.
       =NEG, Use the largest negative value of each trace.
       =ABS, Use the largest absolute value of each trace.
        Preset = none     e.g.   peak abs

SEG    - Start and End time of the GUIDED window.  The existing water bottom
         time in SEGY trace header word INDEX is added to SEG on each trace
         for the actual search window.  Remember that process WBT can be used
         to convert the SEGY water depth to time, and that there may be multiple
         process WBTs in the procs list.
	 e.g.  procs diskin wbt wbt2  ......
         wbt  vel 1500 end         wbt2  guided pos seg -.02 .02 track .005 end
         Preset = none

TRACK  - The maximum deviation, in seconds, the time of the pick
         may have from the previous good pick.  When the time is
         outside (previous pick time +/- track), the previous
         pick time is used.
         Preset = 99.    e.g.  track .05


Obsolete side-echo scanner
-------- --------- ----------
OFFSET - The number of traces between the SeaBeam depth (center of the
         ship) and the reflection point.
         Preset = 3

NSCAN  - The number of traces to scan for the "closest" SeaBeam depth.
         NSCAN/2 traces will be scanned in both forward and aft
         directions.
         Preset = 10


Copyright (C) 1980 The Regents of the University of California
Written by Paul Henkart, Scripps Institution of Oceanography, March 1980
ALL RIGHTS RESERVED.