Whitcraft, Alyssa K.; Vemiote, Eric F.; Becker-Reshef, Inbal; Justice, Christopher O. (2015). Cloud cover throughout the agricultural growing season: Impacts on passive optical earth observations. REMOTE SENSING OF ENVIRONMENT, 156, 438-447.

Abstract
Cloud cover impedes optical satellite remote sensing instruments from obtaining clear views of the Earth's surface. Meanwhile, agriculture is a highly dynamic process, with significant changes in crop biomass and condition often occurring within roughly a week. The Group on Earth Observations Global Agricultural Monitoring (GEOGLAM) Initiative represents international efforts to improve the satellite-based monitoring of agricultural processes at multiple temporal and spatial scales. Within this context, it is necessary to understand how cloud cover impacts the probability of securing reasonably clear views of croplands using passive optical Earth observations as the agricultural growing season progresses. To this end, we employ 10-13 years of twice daily 0.05 degrees MODIS Terra (AM) and Aqua (PM) surface reflectance quality assessment cloud flags to investigate diurnal, geographical, and seasonal (early, mid, late, and non-agricultural growing season) characteristics of cloud cover presence frequency and pervasiveness (amount) over global agricultural areas. To provide insight into the ability of hypothetical missions with two modeled revisit frequencies (f = 2, 4 days) to return reasonably clear views at a rate sufficient to track changes in crop biomass and condition, we show the percentage of 8 day compositing periods throughout the agricultural growing season for which a given clarity requirement (at least 70%, 80%, 90%, or 100% cloud-free) could be met.This research shows that the early and mid-agricultural growing season, which are important periods for crop type area identification and crop yield forecasting, are characterized by both frequent and pervasive cloud extent. Many important agricultural areas during this and other portions of the agricultural growing season are so persistently and pervasively occluded by clouds that less than half of their 8 day composites would be even 70% clear, suggesting that in these areas/time periods, optical, polar-orbiting imaging is not likely to be a viable option for operational monitoring and alternatives (e.g. microwave synthetic aperture radar, SAR) ought to be considered. Further, for most agricultural areas of the world, regardless of seasonality, morning acquisitions are more likely to return reasonably clear views, an important consideration in the planning of future optical, polar-orbiting Earth observing missions with agricultural monitoring science objectives. These results are an important contribution toward the articulation of Earth observation data requirements for global agricultural monitoring. (C)2014 Elsevier Inc. All rights reserved.

DOI:
10.1016/j.rse.2014.10.009

ISSN:
0034-4257