Ultrasonic Spectrum : The frequency span of elastic waves greater than the highest audible frequency, generally regarded as being higher than 2.0 x 10 cycles per second, to approximately 10 cps. (RP 2X)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}