Compute the minimum-amplitude downward continuation filter of Wieczorek and Phillips (1998).

## Usage

wl = DownContFilterMA (l, half, r, d)

## Parameters

wl : output, real(dp)
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(dp)
The reference radius of the gravitational field.
d : input, real(dp)
The radius of the surface to downward continue to.

## Description

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.

## References

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.