Surface-based sonar system could rapidly map the ocean floor at high resolution - Satellite measurements make major seafloor map improvements - Sonar image was not Amelia Earhart plane, exploration team says - New Niwa vessel to study the sea floor in the Hauraki Gulf - Explorer Shackleton's last ship discovered 'intact' on sea floor - as sonar image released - Explorers believe sonar image shows Amelia Earhart's missing plane