While reformatting 600 terabytes of SEG-D data SIOSEIS encountered
several quirks in the SEG-D standard.  


RECORD LENGTH AND NUMBER OF SAMPLES
-----------------------------------
    SIOSEIS was changed to automatically detect datasets with an extra
data sample which was created by a poor definitiion of record length
in a version of the SEG-D standard.  It's the classic "how many samples".
E.G. How many sample are in a 2 second 1 mil trace?".  2000 or 2001?  
SEG-D datasets before Rev 2(?) always used 2000.

NON_SEISMIC DATA
----------------
    SIOSEIS was changed to handle non-seismic data in a way that
is still useful in SEG-Y.  SIOSEIS retains the format of the SEG-D
non-seismic traces when creating the SEG-Y output.  e.g. SEG-D external
data may contain ASCII navigation which will remain ASCII in the
SEG-Y trace.  The SEG-Y trace id (trace header short integer 15) is
set to 0 or "unknown". (I need to see how DISKIN treats id 0).
    See SEG-D external header analysis.
    Only SEG-D channel sets id 1, 8, 9 (seismic data, unfiltered 
signature, filtered signature) are considered seismic and are converted 
using the SEG-D data word format. The SEG-Y output trace of a i
non-seismic trace is just a copy of the input SEG-D trace.  

MP FACTOR
---------
     The SEG-D MP factor is "used to descale the data to obtain input
voltage in millivolts".
     SIOSEIS computes the MP FACTOR differently from two commercial
processing packages which differed from each other too!.  Each is different 
by a constant.  E.g. SIOSEIS is different from Paradigm by a factor of 4.


SEG-Y TRACE ID vs SEG-D CHANNEL SET ID
--------------------------------------
SEG-Y                                   upper nibble
REV 1	description	SEG-D Rev 1	byte 11       	SEGD rev 3 - BCD=Hexidecimal	
  -1	Other
  0	Unknown          	0       unused          00	
  1     seismic data    	1	seismic data	10	
                                                        11	
  2     dead trace              2       time break      20	
                                                        21	
                                                        22	
  3     dummy                   3       uphole          30	
  4     time break              4       water break     40
  5     sweep                   5	time counter    50
  6     sweep                   6       external data   60	
                                                        61
                                                        62
                                                        63
  7     timing                  7       other           70	
  8		8	signature, unfiltered		80	
  9	near-field gun signature	9	signature filtered		90	
  10	far-field gun signature				91	
  B       =      11	seismic pressure sensor				92	
  C     =        12	multicomponent	12	Auxiliary Data Trailer		93	
  13					94	
  14					95	
  15					96	
  16					97	
						
						
					B0	
					B1	
					B2	
					B3	
					C0	
					C1	
					C2	
					C3	
					C4	
					C5	
					C6	
					C7	
					F0