title: Estimating random errors due to shot noise in backscatter lidar observations.
abstract: We discuss the estimation of random errors due to shot noise in backscatter lidar observations that use either photomultiplier tube (PMT) or avalanche photodiode (APD) detectors. The statistical characteristics of photodetection are reviewed, and photon count distributions of solar background signals and laser backscatter signals are examined using airborne lidar observations at 532 nm using a photon-counting mode APD. Both distributions appear to be Poisson, indicating that the arrival at the photodetector of photons for these signals is a Poisson stochastic process. For Poisson- distributed signals, a proportional, one-to-one relationship is known to exist between the mean of a distribution and its variance. Although the multiplied photocurrent no longer follows a strict Poisson distribution in analog-mode APD and PMT detectors, the proportionality still exists between the mean and the variance of the multiplied photocurrent. We make use of this relationship by introducing the noise scale factor (NSF), which quantifies the constant of proportionality that exists between the root mean square of the random noise in a measurement and the square root of the mean signal. Using the NSF to estimate random errors in lidar measurements due to shot noise provides a significant advantage over the conventional error estimation techniques, in that with the NSF, uncertainties can be reliably calculated from or for a single data sample. Methods for evaluating the NSF are presented. Algorithms to compute the NSF are developed for the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations lidar and tested using data from the Lidar In-space Technology Experiment.
authors.affiliation: National Institute of Aerospace, Hampton, Virginia, USA. zliu@nianet.org
authors.forename: Zhaoyan
authors.initials: Z
authors.lastname: Liu
authors.forename: William
authors.initials: W
authors.lastname: Hunt
authors.forename: Mark
authors.initials: M
authors.lastname: Vaughan
authors.forename: Chris
authors.initials: C
authors.lastname: Hostetler
authors.forename: Matthew
authors.initials: M
authors.lastname: McGill
authors.forename: Kathleen
authors.initials: K
authors.lastname: Powell
authors.forename: David
authors.initials: D
authors.lastname: Winker
authors.forename: Yongxiang
authors.initials: Y
authors.lastname: Hu