SystemSizeParam
returns the size parameter calculation
From Rinehart (1997), Eqn 4.9 and 5.7 and Battan Ch. 4.5
SystemSizeParam(D, lam)
R. E. Rinehart, 1997 Radar for Meteorologists Rinehart Publishing
L. J. Battan, 1973 Radar observation of the atmosphere The University of Chicago Press