In spite of the rapid growth in the application of active 3D sensing technologies, it has proved difficult to acquire surface data from transparent objects due to the high transmittance and specularity of the surfaces and the confusion caused by multiple returns. In this paper, we describe how active time-of-flight range sensing using photon counting can be used to acquire data from several transparent surfaces simultaneously. Following a short introduction, the paper is organised in three main

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... sections. First we review the basic principles of time of flight ranging using time correlated single photon counting. Second, we present some basic theory of how data is acquired from multiple surfaces. Third, we present some initial measurements on common transparent objects. Finally, we summarise progress and the necessity for further work.