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                    R E A D M E . V A R I A B L E S 
                    doc: Tue Apr 13 10:51:01 2010
                    dlm: Mon Jun  3 12:35:43 2013
                    (c) 2010 A.M. Thurnherr
                    uE-Info: 30 22 NIL 0 0 72 3 2 4 NIL ofnI
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d-STRUCTURE FIELDS
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d.ts(combo_bin,ensemble)
	- target strength
	- set in [loardri.m]
	- combo_bin is bin number in combined up-/downlooker data
	- look-up combo_bin using d.izd(bin) and d.izu(bin)

d.tg(combo_bin,ensemble)
	- target strength corrected for attenuation and beam spreading
	- calculated in targ() in [getbtrack.m]
	- same format as d.tg

d.izd(bin), d.izu(bin)
	- set in [loadrdi.m]
	- d.izd(1) is first bin of downlooker
	- d.izu(end) is last bin of uplooker

d.z(ensemble)
	- instrument depth

d.izm(combo_bin,ensemble)
	- depth of each measurement

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OUTPUT FIELDS
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dr.ts, dr.ts_out
	- target strength of 2nd & last downlooker bin, respectively
	- scaled to dB using RDI scale factor of 0.45 [loadrdi.m] #1138
	- median of all 4 beams [loadrdi.m] #718
	- super-ensemble average [prepinv.m] #584