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The use of microwave remote sensing opens new possibilities to study global soil moisture dynamics. The measured signal is proportional to the surface moisture and temperature of a thin soil layer. Several low-frequency microwave sensors, such as the Advanced Microwave Scanning Radiometer (AMSR) in C band and Soil Moisture and Ocean Salinity (SMOS) in L band, are now being flown (AMSR) or are scheduled to be launched in the near future (SMOS, in 2005) on sun-synchronous satellite platforms. Because of the diurnal cycle of the measured surface soil moisture content and its temporal variability, the restricted time sampling by an instrument in sun-synchronous orbit may be a source of error in the monthly mean quantities used for climate and land surface processes models. This paper presents a time sampling experiment, conducted with a general circulation model, in order to estimate the …