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###  uw_merge.description  ###
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Description by S.M. Smith January 1995 

Underway marine geophysical data (navigation, depth, magnetics and
gravity) are merged into a single file containing time, position,
depth, magnetic total field and magnetic anomaly, measured gravity
and gravity freeair anomaly by program 'uwmerg'.

Input files to uwmerg are: Navigation	navbin.[CRUISE]
			   Depth	dep_uwts.[CRUISE]
			   Magnetics    mag_uwts.[CRUISE]
			   Gravity      grav_uwts.[CRUISE]

		Output file:		uwmrg.[CRUISE]

See 'uwmrg.file.description' [not onboard R/V Melville in Jan 1995;
the following is a brief overview]:

Time:           Unix Seconds (since 0000z/1January1970)

Position:	Latitude:  minutes and (parts_of_minutes * 10000) 
			     north of South pole
		Longitude: minutes and (parts_of_minutes * 10000)
			     east of Prime Meridian

Depth:	Two way travel time in seconds * 10000

Magnetic Total Field:	in nanoTessla * 10
Magnetic Anomaly:	in nanoTessla * 10

Gravity Measured:	in mgal * 100
Gravity Freeair:        in mgal * 100

Magnetic Anomaly:
-----------------
The magnetic anomaly is calculated by subtracting the International
Geomagnetic Reference Field (IGRF) from the total field value. (The
IGRF is calculated by determining the IGRF values at the corners of a
one degree square centered on the first point and then interpolating
the IGRF on this plane as long as the location of subsequent values
stay within the one degree square.)

Gravity Freeair Anomaly:
------------------------
### notes on gravity corrections taken from uwmerg.f program

c	EOTVOS CORRECTION:
c	Coefficients based on World Geodetic System 1972 (WGS-72) ellipsoid.  
c	Reference: Bowditch, Nathaniel, American Practical Navigator,
c		   (1984 edition), Appendix D (page 1173).
c		   SIO library call #: VK/555/A48/1984/v.1
c	   omega (earth angular velocity) = 7.2921e-5 rad/sec
c	   erad (earth radius) = 6378135 meters
c	   xkmsec (knots to m/sec) = 0.51444
c	eotvos.cor (mgal) = (2.0 * omega * spd.east(m/sec) * cos(lat)
c				+ speed(m/sec)**2/erad) * 1.0e5
c
c	result when input speed is in knots:
c
  	  etvos = (7.50271 * sin(cse * radeg) * cos(flat) 
     *		  + 0.00414931 * spd) * spd
c
c
c	INTERNATIONAL GRAVITY FORMULA 1967:
c	Based on Geodetic Reference System 1967.  
c	Reference: Geodetic Reference System 1967,
c		   International Association of Geodesy, 
c		   Special Publication No. 3, (page 60). 
c		   SIO library call #:SIO/QB/321/.I6/1967 (missing
c		   as of Aug88, obtain through Inter-library Loan).
c
c		   See also: G.P. Wollard,1979, Geophysics,v.44
c		   no.7,pp 1352-1366; 
c		   SIO library call #:SIO/1/GE7864/v.44/no.7-12
c
c	(Note, the form used below is the Chebychev approximation
c	which has a maximum error of 0.004 mgal.  According to
c	Spec. Pub. No. 3, the formula can also be expressed as a 
c	conventional series which is less accurate (0.1 magal) 
c	and requires sin (2*lat) ).
c	In calculations below, "sqsl" = sin(lat in radians) squared.
c
	grs67 = 978031.846 * (1.0 + 0.005278895 * sqsl
     *          + 0.000023462 * sqsl * sqsl)

	  mvalue(4) = nvald(3) 
c
c
c	free air anomaly (mgal*100) = meas.grav - grs67 + eotvos.corr
c
	mvalue(5) = mvalue(4) + (etvos - grs67) * 100. + 0.5


UWMLST ASCII LIST OUTPUT 
------------------------
Program 'uwmlst' produces an ASCII listing file from the uwmrg file.
This listing contains the contents of the uwmrg file but converts depth
to meters (1500m/sec assumed sound velocity and corrected by Carter
Tables) and adds course and speed fields. All header lines in the
'uwmlst.[CRUISE]' file begin with a "#" character, allowing these lines
to be stripped out by use of the  Unix command grep -v "^#" uwmlst.file. 
(see 'uwmlst.file.description').

MGD77 EXCHANGE FORMAT OUTPUT
----------------------------
Script 'DOtmgd77' takes input files 'uwmrg.[CRUISE]' and 'mgdhdterm.[CRUISE]
and creates a 'mgd77.[CRUISE]' file in the MGD77 Exchange Format.

Note, the MGD77.[CRUISE] file is blocked, i.e. no newline characters
at the end of each 120 character logical record.

#end