Read the excerpt below and answer the question.
lying, robed in snowy white
that loosely flew to left and right -
the leaves upon her falling light-
through the noises of the night
she floated down to camelot:
and as the boat-head wound along
the willowy hills and fields among,
they heard her singing her last song,
the lady of shalott.
what is the basis for the imagery used in the underlined selections?