An Improved Technique for Producing MPL Backscatter Profiles Properly Characterized at All Ranges
Flynn, C.J. and Powell, D.M., Pacific Northwest National Laboratory
Eleventh Atmospheric Radiation Measurement (ARM) Science Team Meeting
An important part of ARM's mission is the quantitative study of the effect of clouds and aerosol on radiative transfer and the energy budget. Micropulse Lidar (MPL) are an integral component of the ARM Program's measurement strategy with one deployed at each of the four major sites (SGP, TWP1, TWP2, and NSA). The MPL system is capable of producing vertical profiles of cloud and aerosol from ground level to the top of the atmosphere. However, the legitimacy of these profiles is sensitive to the calibration and system corrections of the individual MPL. In particular, the MPL is susceptible to optical alignment problems which reduce the accuracy of these corrections. This issue is relevant to historical data sets as well as to the state of ongoing collections. We present a two-stage technique for addressing this problem. We first determine corrections to achieve proper far-range behavior by comparing vertical MPL profiles against a theoretical Rayleigh atmosphere. This stage requires background-subracted, afterpulse-subtracted, range-corrected MPL profiles where no significant cloud or aerosol return is evident above a few kilometers. It assumes that the scattering above this range is purely Rayleigh molecular scattering. As a second stage, proper near-range behavior is then achieved using horizontal measurements under homogeneous conditions. The net result is a lidar profile properly characterized at all ranges.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
