What is a GTD Analyser?

Answer 1

GTD is a model for high resolution radar signal processing or processing of telescopic signals. It stands for Geometrical Theory of Diffraction.

Cited below is the abstract of a paper describing its use with radar. I have also cited a paper discussing its use with telescopes.

The 3rd citation is actually for a book entitled "Geometrical Theory of Diffraction."

Hope one of those helps! :-)