def ndvi_filter_site(image_directory):
    
    """A function that extracts the site name from the imagery path name

    Parameters
    ----------
    directory: directory to file including study 
    site e.g: "'HARV/landsat-crop/LC080130302017031701T1-SC20181023151837'"
    
    Returns
    -------
    Date string of the image site

    """
    filter_path = image_directory
    filter_site = filter_path[0:4]

    return filter_site