Process XSTAR
                     ------- -----

Parameters, alphabetically:
binpath  deltad    depth     dummies   ftr       lprint   
ltr      mkreal    type      weights   wireout   xyzpath

Document Date: 29 June 2006
Modifications:
   Add TYPE 3 - Mar. 03
   Add parameter MKREAL - Jan. 05
   Add parameter dummies 2 - Jan. 05
   Add TYPE 5 - Aug. 05
   Add TYPE 4 - June 06

     Process XSTAR converts EdgeTech's chirp analytic data into a
more "standard SEG-Y" format and performs several signal processing
steps so that the data are more like conventional time series data.
Process XSTAR applies trace scaling and a complex modulus:
scalar = buf(51) / 32767. * 1.41E-14
trace(i) = scalar * SQRT( real * real + imag * imag).
     As a result of the complex modulus, the output of process XSTAR
has half as many samples as the input AND twice the sample interval.
The complex modulus of the analytic data creates the envelope.

     EdgeTech does not follow the SEG-Y standard, consequently the
data must be converted to SEG-Y.  GeoStar data are in PC byte order
and are missing the SEG-Y file header; GeoStar data must be converted
to using program gstar2segy.  Xstar data must be identified to SIOSEIS
in process DISKIN using parameter     format edgetech. 
(GeoStar data must not use it).

*****      Use DISKIN parameter     format edgetech      *****

     Parameter TYPE is required so that process XSTAR knows which
type of data it has.  
0 = GeoStar, 
1 = 1 trace Xstar, 
2 = 2 trace Xstar.
3 = 2 trace, where trace 1 is envelope and trace 2 is analytic.
4 = 2 trace Xstar without summing the traces.
5 = Xstar Version 5

     Of the two known XSTAR systems, one has two transducers and
the other one, as evidenced by the number of output traces they
produce.  Process XSTAR corrects most of the SEG-Y idiosyncracies
these systems produce (such as counting trace numbers from 0 and
setting the number of traces per ping to two when there are two
traces!).  The two traces of the dual transducer Xstar are 
automatically summed in process Xstar unless parameters FTR/LTR 
are given or TYPE 4 is specified.

     There are many different pulses available on Edgetech 
fish, but the pulse name is not recorded in the data.

     Towed fish data are hard to interpret if there is much
variation in the fish depth.  It is possible to remove this
variation and shift all the data to a datum.  If the fish
recorded the source and receiver depth/elevation in the SEG-Y
trace header, use process SHIFT parameters DATUMV and DATUME.
     If the fish did not have a depth sensor, several schemes
have been used to determine the fish depth.  See the SIOSEIS
examples for a method when in shallow water.  It is also possible
to do a datum correction if the water depth is known.  The
known water depth may be described via an XYZ file.  SIOSEIS
process WBT may be used to pick the water bottom return from
the chirp data and process HEADER can be used to save the pick
for the next chirp ping.  Process XSTAR can compute the depth
of the fish given the water depth at the fish and the fish
depth.  Parameter WIREOUT is used to locate the fish behind
the position (lat/long) in the SEG-Y header of each ping.  See
the 1999 Eel River example for a detailed discussion of a datum
correction given XYZ and WIREOUT.




Simple Example:
sioseis << eof
procs diskin xstar filter diskoa end
diskin
   format edgetech
   ipath /home/vol3/henkart/eel/yr2000day196-1915z.xstar end
end
xstar
   type 2 end
end
diskoa
    opath /home/vol3/henkart/eel/yr2000day196-1915z.segy end
end
filter
   pass 500 1000 end
end
end
eof


REQUIRED PARAMETERS
-------- ----------
TYPE    - The type of Edgetech chirp used.
        = 0, GeoStar.
        = 1, 1 trace Xstar
        = 2, 2 trace Xstar where the output is a single trace formed by
             summing the two input traces AFTER the envelope is formed.
        = 3, 2 trace Xstar where each output trace is just the envelope.
             The two traces are NOT stacked, however the "end-of-gather"
             flag is set on trace two so that process stack will work.


OPTIONAL PARAMETERS
-------- ----------
MKREAL  - A yes/no switch when set to YES indicates that the output
          trace should be the frequency corrected time domain trace.
          Preset = no.       e.g. yes

DUMMIES - A switch indicating how the program should treat missing
          pings or a missing ducer on the dual ducer xstar. 
          Inserting dead traces for missing pings is useful to keep
          the horizontal scale constant when plotting.
        =0, missing pings are not output.
        =1, dead traces are created for missing pings.
        =2, Valid with the dual ducer (type 2) only.  When 1 ducer
          is missing, the single trace is scaled and output.  Missing
          pings are replaced by dead traces.
          Preset = 1.        e.g. dummies 2 type 2

FTR/LTR - The first and last trace to use.  Only applicable with two
          trace Xstar data.   ftr 1 ltr 1 indicates trace 2 will be
          ignored.  ftr 2 ltr 2 indicates trace 1 will be ignored.
          ******   It is suggested that the user verify that the two
          ******   traces are similar before stacking the two traces.
          ******   i.e. One trace might be noiser that the other and
          ******        should not be used.

WEIGHTS - A list of weights to apply to the traces before summing
          (On Driscoll's XSTAR only since it has two traces!).
          Preset = 1 1

XYZPATH - The pathname of an ASCII file with longitude,
          latitude, and elevation of the fish.  SIOSEIS will
          find the closest XYZ position for every trace and
          inserts the fish depth into SEGY short integer header 
          word 16 and the floating point two way travel time
          into SEGY floating point word 50 ( depth / 750. ).
          Fish depth = - fish elevation.  The longitude and
          the latitude must be in decimal degrees and the fish
          elevation must be negative meters.  e.g
          -124.438095 40.650543 -52.921194
          -124.437859 40.650543 -52.381282
          -124.437614 40.650543 -51.851186

          The floating point two way travel time to the fish
          is needed because of the high sampling rate of the
          XSTAR fish.  One meter is several samples.

          Preset = " ".    e.g.   xyzpath Eureka.xyz

BINPATH - SIOSEIS converts the ASCII file into binary for internal
          use since ASCI I/O is quite time consuming.  The binary
          file may be saved and reused by giving this parameter.
          Preset = "xyz.bin".    e.g.   binpath my_xyz.bin

WIREOUT - The distance of the fish from the boat as measured by the
          amount of wire let out.  If the source (fish) depth is in
          the SEG-Y header from the previous ping, process XSTAR will
          calculate the water depth at the fish rather than the boat
          when an XYZ file is given.

LPRINT - SIOSEIS debug print switch.  A bit switch.
       =4, The fish lat/long are printed if XYZPATH is given.
       =8, The XYZ file lat/long/depth used is printed.

DELTAD - A warning is printed when the closest XY is greater than
         DELTAD meters away.
         Preset = .01    e.g.   deltad .0004


Written by:  Paul Henkart, Scripps Institution of Oceanography, October 2001
Copyright (C) The Regents of The University of California
All Rights Reserved.
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