Rapid optical method for logging dust concentration versus depth in glacial ice

We describe the design and simulated response of a dust logger consisting o f a downward-pointing phototube, similar to2 m below side-directed light-em itting diodes (ZEDs), attached to a cable that can lower the device down a 3-in. (7.5-cm) borehole filled with butyl acetate. ZED photons that enter t he ice are scattered or absorbed by dust grains, and those that reach the p hototube provide a measure of dust or volcanic ash concentration at a given depth. An increased dust concentration associated with an ancient colder c limate will usually result in an increase in collected light, but may decre ase collected light if air bubbles are present. Centimeter-thick volcanic a sh hands can also be detected. The concept is based on six years of experie nce with pulsed light sources used to measure optical properties of deep An tarctic ice. (C) 2001 Optical Society of America.