Ultrasound independent Advisory Group on Non-ionising Radiation (AGNIR) produced a report in 2010, which was published by the UK Health Protection Agency (HPA). This report recommended an exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above). Ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz (20,000
Above and Below seeks to "recreate the experience and feeling" of the underwater landscapes through use of various thickness of wire. Three-fifths of the artwork depict the Bluespring Cavern with the last two sections depicting what is beneath the water level in the cave. "Above and Below" was fabricated at Walla Walla Foundry in Washington utilizing the bathymetric data gathered from the river bottom and cavern ceiling. Lin's studio translated the data into a collection of contour curves and then sent them to the Foundry. The aluminum tubing was carefully bent to match the computer-generated templates created by the studio then hung within