Extracts contents of SMAP dataSource:
Extracts datasets from SMAP data files.
A data frame produced by
download_smap()that specifies input files from which to extract data.
The path in the HDF5 file pointing to data to extract.
dataset must refer specifically the
group and name within group for the input file, such as can be obtained with
list_smap(). This function will extract that particular dataset,
returning a Raster object.