We present an orbit/scan/geolocation model for systems based on a rotating mirror—such as the Along Track Scanning Radiometer (ATSR) and the Advanced Very High Resolution Radiometer (AVHRR). For ATSR-2, we show how the Bi-directional Reflectance Distribution Function (BRDF) is sampled at different latitudes and times of year. We calculate the shape and weighting functions of the ground resolution elements and the local sampling behaviour. We conclude that, for strongly heterogeneous scenes, a simple map of the nadir data onto the forward data may not suffice. We discuss two of the possible telemetry schemes proposed for ATSR-2. In one there is lower spatial resolution. In the other the swath width is reduced and the inter-visit time increased.