  There is a large number of data archives and web services offering free
access to multispectral satellite imagery. Images from multiple sources are
increasingly combined to improve the spatio-temporal coverage of measurements
while achieving more accurate results. Archives and web services differ in
their protocols, formats, and data standards, which are barriers to combine
datasets. Here, we present RGISTools, an R package to create time-series of
multispectral satellite images from multiple platforms in a harmonized and
standardized way. We first provide an overview of the package functionalities,
namely downloading, customizing, and processing multispectral satellite imagery
for a region and time period of interest as well as a recent statistical method
for gap-filling and smoothing series of images, called interpolation of the
mean anomalies. We further show the capabilities of the package through a case
study that combines Landsat-8 and Sentinel-2 satellite optical imagery to
estimate the level of a water reservoir in Northern Spain. We expect RGISTools
to foster research on data fusion and spatio-temporal modelling using satellite
images from multiple programs.
