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Title:   Author  item
                                            LEI, FANGNI - Wuhan Universityitem
                                            Crow, Wadeitem
                                            SHEN, HUANFENG - Wuhan Universityitem
                                            PARINUSSA, R.M. - University Of New South Walesitem
                                            HOLMES, T. - Science Systems, Inc
  Submitted to: Remote Sensing
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 10/1/2015
                                    Publication  Date: 10/15/2015
                                    Citation: Lei, F., Crow, W.T., Shen, H., Parinussa, R., Holmes, T. 2015. The impact of acquisition times on the accuracy of microwave soil moisture retrievals over the contiguous U.S. 7(10)13448-13465. doi: 10.3390/rs71013448.Interpretive Summary: Satellite-derived estimates of surface soil moisture are increasingly being used for a wide-variety of agricultural applications including: drought monitoring, numerical weather prediction, and flood forecasting. However, a key unresolved issue is the optimal time of day for satellite overpasses designed to measure soil moisture – especially for high-biomass agricultural regions. This issue has been addressed in a number of previous theoretical or plot-scale studies; however, this paper is the first to empirically examine it (at a continental-scale) using real satellite products. The results of the study offer new insight into the design of optimal soil moisture satellite missions for the retrieval of surface soil moisture during high-biomass conditions within agricultural landscapes. As a result, it will be used by operational drought monitoring to maximize our ability to detect the onset and severity of summer agricultural drought within intensively-cultivated areas with the United States Corn Belt.
                                Technical Abstract: Satellite-derived soil moisture products have become an important data source for the study of land surface processes and related applications. For satellites with sun-synchronous orbits, these products are typically derived separately for ascending and descending overpasses with different local acquisition times. Moreover, diurnal variations in land surface conditions, and the extent to which they are accurately characterized, lead to distinct systematic and random error characteristics in ascending versus descending soil moisture products. Here, we apply two independent evaluation techniques (triple collocation and direct comparison against sparse ground-based observations) to quantify (correlation-based) accuracy differences in satellite-derived surface soil moisture acquired at different local acquisition times. The orbits from different satellites are separated into two overpass categories: AM (00:00 to 11:59 Local Solar Time) and PM (12:00 to 23:59 Local Solar Time). Results demonstrate how patterns in the accuracy of AM versus PM retrieval products (obtained from a variety of active and passive microwave satellite sensors) vary according to land cover and across satellite products with different local acquisition times.


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