Aglite lidar: calibration and retrievals of well characterized aerosols from agricultural operations using a three-wavelength elastic lidar

Abstract

Lidar (LIght Detection And Ranging) provides the means to quantitatively evaluate the spatial and temporal variability of particulate emissions from agricultural activities. AGLITE is a three-wavelength portable scanning lidar system built at the Space Dynamic Laboratory (SDL) to measure the spatial and temporal distribution of particulate concentrations around an agricultural facility. The retrieval algorithm takes advantage of measurements taken simultaneously at three laser wavelengths (355, 532, and 1064 nm) to extract particulate optical parameters, convert these parameters to volume concentration, and estimate the particulate mass concentration of a particulate plume. The quantitative evaluation of particulate optical and physical properties from the lidar signal is complicated by the complexity of particle composition, particle size distribution, and environmental conditions such as heterogeneity of the ambient air conditions and atmospheric aerosol loading. Additional independent measurements of particulate physical and chemical properties are needed to unambiguously calibrate and validate the particulate physical properties retrieved from the lidar measurements. The calibration procedure utilizes point measurements of the particle size distribution and mass concentration to characterize the aerosol and calculate the aerosol parameters. Once calibrated, the Aglite system is able to map the spatial distribution and temporal variation of the particulate mass concentrations of aerosol fractions such as TSP, PM 10 , PM 2.5 , and PM 1. This ability is of particular importance in the characterization of agricultural operations being evaluated to minimize emissions and improve efficiency, especially for mobile source activities.

Integration of remote lidar and in-situ measured data to estimate particulate flux and emission from tillage operations

“…The details of this approach described in our recent publications [1,6]. In summary, these point measurements are used to establish the parameters required to invert the lidar data and retrieve the aerosol concentration.…”

“…Secondly the signal-to-noise ratio (SNR) of the lidar return signal strongly decreases with the distance and the retrieval errors consequently degrade when reference point is chosen far away from the lidar. In most of practical cases it leads to the strong decrease in the accuracy of retrievals [6]. If the boundary point can be placed at a range relatively close to the instrument where the signal-to-noise ratio (SNR) is still high the accuracy of lidar retrieval and calibration will increase significantly.…”

“…The process of retrieving aerosol mass concentration from the Aglite lidar data is discussed in details in our previous publications [6,10]. The retrieval process can be summarized as following (see Figure 2).…”

“…Light detection and ranging (lidar) technology has been successfully applied to qualitatively characterize particulate emissions from agricultural sources [1][2][3]. The physical properties of an aerosol can be retrieved from lidar data using the measured backscatter coefficients and the known relationship between aerosol physical properties and backscatter [4][5][6]. This study used advanced measurement technologies such as lidar system [7] coupled with conventional point measurement air quality samplers to map PM emissions at high spatial and temporal resolutions [1,6], allowing for accurate comparisons of the Conservation Management Practices (CMP) under test.…”

“…The physical properties of an aerosol can be retrieved from lidar data using the measured backscatter coefficients and the known relationship between aerosol physical properties and backscatter [4][5][6]. This study used advanced measurement technologies such as lidar system [7] coupled with conventional point measurement air quality samplers to map PM emissions at high spatial and temporal resolutions [1,6], allowing for accurate comparisons of the Conservation Management Practices (CMP) under test. The purpose of this field study was to determine whether and how much particulate emission differs from the conventional method of agricultural fall tillage and a "Combined Operations" Conservation Management Practice.…”