Compute the minimum-amplitude downward continuation filter of Wieczorek and Phillips (1998).
wl = DownContFilterMa (l, half, r, d)
wl : output, real*8
: The amplitude of the downward continuation filter.
l : input, integer
: The spherical harmonic degree.
half : input, integer
: The spherical harmonic degree where the filter is equal to 0.5.
r : input, real*8
: The reference radius of the gravitational field.
d : input, real*8
: The radius of the surface to downward continue to.
DownContFilterMA will calculate the downward continuation filter of Wieczorek and Phillips (1998; eq. 19) for a given spherical harmonic degree l. The input parameters include half, which is the degree where the filter is equal to 0.5, and r and d, which are the reference radius of the gravitational field and the radius of the surface to downward continue to, respectively.
Wieczorek, M. A. and R. J. Phillips, Potential anomalies on a sphere: applications to the thickness of the lunar crust, J. Geophys. Res., 103, 1715-1724, 1998.