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We have investigated how the quality of stereoscopically measured topography degrades with varying illumination, in particular theranges of incidence angles and illumination differences over which useful digital topographic models (DTMs) can be recovered. Ourapproach is to make high-fidelity simulated image pairs of known topography and compare DTMs from stereoanalysis of theseimages with the input data. Well-known rules of thumb for horizontal resolution (>3–5 pixels) and matching precision (~0.2–0.3pixels) are generally confirmed, but the best achievable resolution at high incidence angles is ~15 pixels, probably as a result ofsmoothing internal to the matching algorithm. Single-pass stereo imaging of Europa is likely to yield DTMs of consistent (optimal)quality for all incidence angles ≤85°, and certainly for incidence angles between 40° and 85°. Simulations with pairs of images inwhich the illumination is not consistent support the utility of shadow tip distance (STD) as a measure of illumination difference, butalso suggest new and simpler criteria for evaluating the suitability of stereopairs based on illumination geometry. Our study wasmotivated by the needs of a mission to Europa, but the approach and (to first order) the results described here are relevant to a widerange of planetary investigations

THE EFFECT OF ILLUMINATION ON STEREO DTM QUALITY: SIMULATIONS IN SUPPORT OF EUROPA EXPLORATION