title: An effective approach for gap-filling continental scale remotely sensed time-series.
abstract: The archives of imagery and modeled data products derived from remote sensing programs with high temporal resolution provide powerful resources for characterizing inter- and intra-annual environmental dynamics. The impressive depth of available time-series from such missions (e.g., MODIS and AVHRR) affords new opportunities for improving data usability by leveraging spatial and temporal information inherent to longitudinal geospatial datasets. In this research we develop an approach for filling gaps in imagery time-series that result primarily from cloud cover, which is particularly problematic in forested equatorial regions. Our approach consists of two, complementary gap-filling algorithms and a variety of run-time options that allow users to balance competing demands of model accuracy and processing time. We applied the gap-filling methodology to MODIS Enhanced Vegetation Index (EVI) and daytime and nighttime Land Surface Temperature (LST) datasets for the African continent for 2000-2012, with a 1 km spatial resolution, and an 8-day temporal resolution. We validated the method by introducing and filling artificial gaps, and then comparing the original data with model predictions. Our approach achievedR2values above 0.87 even for pixels within 500 km wide introduced gaps. Furthermore, the structure of our approach allows estimation of the error associated with each gap-filled pixel based on the distance to the non-gap pixels used to model its fill value, thus providing a mechanism for including uncertainty associated with the gap-filling process in downstream applications of the resulting datasets.
authors: Spatial Ecology and Epidemiology Group, Tinbergen Building, Department of Zoology, University of Oxford, Oxford, UK.
authors: Daniel J
authors: DJ
authors: Weiss
authors: Geography and Environment, University of Southampton, University Road, Southampton SO17 1BJ, UK.
authors: Peter M
authors: PM
authors: Atkinson
authors: Spatial Ecology and Epidemiology Group, Tinbergen Building, Department of Zoology, University of Oxford, Oxford, UK.
authors: Samir
authors: S
authors: Bhatt
authors: Spatial Ecology and Epidemiology Group, Tinbergen Building, Department of Zoology, University of Oxford, Oxford, UK.
authors: Bonnie
authors: B
authors: Mappin
authors: Spatial Ecology and Epidemiology Group, Tinbergen Building, Department of Zoology, University of Oxford, Oxford, UK ; Fogarty International Center, National Institutes of Health, Bethesda, MD, USA.
authors: Simon I
authors: SI
authors: Hay
authors: Spatial Ecology and Epidemiology Group, Tinbergen Building, Department of Zoology, University of Oxford, Oxford, UK.
authors: Peter W
authors: PW
authors: Gething
keywords: Africa; EVI; Gap-filling; LST; MODIS
references: Adv Parasitol. 2006;62:37-77
references: 16647967
references: PLoS One. 2008 Jan 09;3(1):e1408
references: 18183289