Range-resolved co-pointing multiple wavelength lidar backscatter from aerosols is analyzed for a summer day in the northeast United States. Lidar backscatter wavelengths are 355 nm, 532 nm, and 1064 nm and were measured at a vertical range gate of 60 meters. The altitude range of lidar measurement is from the surface to 4 km above ground level and the measurement period spanned five hours from late afternoon through several hours after sunset. Vertical profiles of temperature, relative humidity, and wind velocity, and surface visibility, were also measured to characterize the prevailing air mass. Lidar aerosol backscatter was significant through 3 km and diminished rapidly above. Several aerosol models selected on an a priori basis are used to compute backscatter ratios for wavelength pairs using scattering theory. These are compared with the profiles of measured backscatter ratios in an attempt to infer the type of aerosol present in the lower atmosphere and estimate multiple wavelength extinction. Measured backscatter ratios agreed with the ratios for soot, water-soluble, and haze aerosol models at the lowest altitudes with little agreement above 1 km for any model. Extinction estimates derived from lidar backscatter at 300 m were significantly higher than the corresponding values deduced from surface observations.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.