This paper presents a comparison of the two main techniques for measuring the direction of arrival of signals that have been proposed for implementation on a topside sounding satellite. The assumption is that the topside sounder would be a payload on a Surrey Satellite Technology Limited (SSTL) satellite. The two candidate methods are amplitude direction finding (DF) where the relative amplitude on two (or more) receiving antennas is compared, and an interferometric method where the relative phases of reception on two antennas separated in space are compared. A novel interferometric “synthetic aperture” method (SARDF) for across track DF is reported for the first time in this paper. This method is particularly well suited for providing the pulse signal returns in a form suitable for along track synthetic aperture measurements. The two methods are compared using a simple information theoretic approach to assess how angular accuracy is limited with respect to signal to noise ratio, pulse length and ionospheric roughness.