In this work, which was managed by GEC-Marconi Research Centre under contract to ESTEC, an investigation has been performed into the temporal variation and contemporality of SAR and optical, high resolution remote sensing data. The primary aim of the study is to investigate the combination of SAR and optical data to determine, in the application areas of the cryosphere and hydrology, the so-called 'synergistic' temporal sampling requirements, i.e. the time interval within which both optical and SAR data must be recorded in order to derive a particular ground parameter or give a specified improvement. Given that the different viewing geometries of SAR (side-looking) and optical (nadirpointing) sensors would prevent the same area from being imaged simultaneously from the same platform, the resulting temporal sampling requirements are analysed to assess whether single-platform satellites combining SAR and optical sensors would be feasible in future missions for the various application areas considered. The results indicate that single-platform satellites could be used for such application areas in all cases except for the most stringent (1 day) sampling requirements.