def prepare_collections_list(in_platform):
    """
    Basic function that takes the name of a satellite 
    platform (Landsat or Sentinel) and converts 
    into collections name recognised by dea aws. Used only
    for ArcGIS Pro UI/Toolbox.
    
    Parameters
    -------------
    in_platform : str
        Name of satellite platform, Landsat or Sentinel.
    
    Returns
    ----------
    A string of dea aws collections associated with input 
    satellite.
    """
    
    # checks
    if in_platform not in ['Landsat', 'Sentinel']:
        raise ValueError('Platform must be Landsat or Sentinel.')
        
    # prepare collections
    if in_platform == 'Landsat':
        return ['ga_ls5t_ard_3', 'ga_ls7e_ard_3', 'ga_ls8c_ard_3']
    
    elif in_platform == 'Sentinel':
        return ['s2a_ard_granule', 's2b_ard_granule']