How frequent the Landsat 8/9-Sentinel 2A/B virtual constellation observed the earth for continuous time series monitoring

The synergy of Landsat 8/9 and Sentinel 2A/B in the formation of a virtual constellation marked a significant advancement in high spatiotemporal time series monitoring. However, the presence of contaminations, including clouds, snow/ice, and shadows, had notably impacted the quality of image acquisition. The practical monitoring capacity of this constellation, particularly in terms of time scale, had not been exactly investigated. Therefore, this study proposed an evaluation method for the minimum time scale, accounting for the temporal discontinuity induced by contaminations. It was found that while the average revisit period of constellation was as short as 2.7 days, the effective period degraded to 5.5 days after the removal of contaminated observations. In considering continuous monitoring along with time series, the practical monitoring scale, referred to as the ideal period, was significantly longer than the effective period. Consequently, it was observed that roughly 80 % of global land (excluding Polar regions) could achieve a minimum time scale of only weekly monitoring. These findings underscored the potential overestimation of the practical capacities for the virtual constellation in previous knowledge, offering valuable insights for policymakers in determining the appropriate frequency and timing of satellite applications.