What is EARL?
EARL is a LIDAR machine that uses a 523.5 nanometer-wavelength laser to beam laser light up into the sky to collect data about the atmosphere. The laser light scatters off of particles in the atmosphere, and the light that scatters at 180 degrees returns straight back where it came from--EARL itself. Part of the EARL assembly are two mirrors that focus the laser light into a receiver that splits the received light into two channels: long range and short range. The long range channel is used to better observe the upper parts of the atmosphere, above 4,000 meters. The short range channel works better with light received from below 4,000 meters. A photomultiplier tube converts the light received into voltage, which is then translated into binary code by the EARL Electronics Box, which contains a digitizer. The information is then read by the computer, and the user observes real-time data on the screen with a LabPro program called RunEarl. Later on, after a full data run where enough data has been compiled, a user can run a Matlab script called ProcEarl to read the files saved by RunEarl to see what happened in the atmosphere over the course of the data run.
Still confused? Want further information? Try the video below.
Haviland Forrister, Agness Scott graduate class of 2012, explains how the EARL system works using the apparatus itself and several graphs of data that she did her research on.