Scholarly reference for IDW variable radius algorithm

I'm trying to come up with a scholarly reference for the variant Inverse Distance Weighting algorithm where only the closest N points are used. The Wikipedia page for IDW lists it at the bottom under the heading Modified Shepard's Algorithm, bu开发者_运维技巧t the information there is pretty sketchy.

This algorithm is in common use in the GIS world (see the bottom of this ArcGIS Desktop Help page for a simple description). Does anyone know of a better (preferably authoritative) reference?

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The citation in the Wikipedia page is the original paper by Shepard, and is heavily cited. It does not get more authoritative than that. Otherwise, a good book on remote sensing or GIS could be an adequate reference.

The modified Shepard version is attributed to Franke and Nielson in this paper, and is also heavily cited in the literature (you can get an idea of citation counts in Google Scholar).