Nighttime near-ground hyperspectral imaging for urban scale remote sensing of aerosols Yael Etzion 1 , David M. Broday 1 , Tsafrir Kolatt 3 , and Maxim Shoshany 2 1 Department of Environmental and Water Resources Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel 2 Department of Transportation and Geo-Information Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel 3 ASI – Applied Spectral Imaging Ltd. Migdal-HaEmek 10511, Israel Keywords: remote sensing, urban scale, fine PM, hyperspectral imaging Spatiotemporal variations in size attributes of ambient aerosols, in particular fine PM, are important estimates for public health risk assessment. Both satellite and ground remote sensing (RS) are applied for characterizing atmospheric aerosols by analyzing the aerosol interactions with electromagnetic radiation in multiple visible-NIR wavelengths or multiple angles. Relying on solar radiation, these methods are limited by sun elevation angle and the cloud cover, and also by the revisit periods and variability of surface albedo for satellite-borne sensors. Current RS procedures can provide estimates of bi-modal size distributions in vertical atmospheric columns (Wang et al., 1996). However, the correlation between the vertical aerosol profiles and ground-level particulate matter (PM) distribution at the urban-scale resolution is highly influenced by the geo-site specific seasonality and the corresponding mixing layer height (Schäfer et al., 2008). The aim of this study was to extract the size attributes of PM in the accumulation mode obtained by hyperspectral imaging through horizontal open paths of 1-4km between the camera and the imaged targets. For this, a camera that acquires high resolution spectral signatures in the visible-NIR range (VDS Vosskühler Cool-1300Q, =400- 1100nm, 160-180 wavelengths) has been used to measure variations in PM accumulation modes. A dedicated procedure was developed by exploiting nocturnal illumination sources as a novel concept for urban scale horizontal RS, as well as an innovative solution for nighttime when solar radiation cannot be used. A laboratory scale feasibility study has been conducted in a dedicated optic chamber. Aerosol optical thicknesses (AOT) between 0.02-1.00 were generated in order to emulate AOT levels in urban regions over 1km open path. Analysis of the hyperspectral sensor response to halogen illumination showed highest sensitivity to AOT in the range of =550-900nm, which allowed for retrievals of fine modes concentrations in diameter range of 0.5- 1.6m, based on Mie calculations. Periodical field scale imaging of remote street lights was performed next. This report focuses on the field-scale imaging and the analysis of extinctions in radiation during extreme dust and haze events, aimed to retrieve potential content of fine modes, by using spectral trends in attenuation (Figure 1). Figure 1. Hyperspectral camera response to a dust event along a 1 km open path in Octber 2008. Spectral signature of a street lamp (top) and the attenuation trend in the main emission range of the lamp (bottom). Bibliography Schäfer, K., Harbusch, A., Emeisa, S., Koepke, P., & Wiegner, M (2008). Atmospheric Environment 42, 4036–4046. Wang, P., Kent, G. S., McCormick, M. P., Thompson, L. W., & Yue, G. K. (1996).Applied Optics 35, 433-440.