def _sensor(product_id):
    """Find sensor ID from product ID."""
    sid = product_id[:2]
    if sid == 'LC':
        return 'OLI_TIRS'
    elif sid == 'LO':
        return 'OLI'
    elif sid == 'LE':
        return 'ETM'
    elif sid == 'LT':
        return 'TM'
    elif sid == 'LM':
        return 'MSS'