An airborne continuous wave (CW) focused CO2 Doppler lidar and a ground-based pulsed CO2 Doppler lidar were used to obtain seven pairs of comparative measurements of tropospheric aerosol backscatter profiles at 10.6 μm wavelength, near Denver, Colorado, during a 20-day period in July 1982. In regions of uniform backscatter the two lidars show good agreement, with differences usually less than ~50% near 8-km altitude and less than a factor of 2 or 3 elsewhere but with the pulsed lidar often lower than the CW lidar. Near sharp backscatter gradients the two lidars show poorer agreement, with the pulsed lidar usually higher than the CW lidar. Most discrepancies arise from a combination of atmospheric factors and instrument factors, particularly small-scale areal and temporal backscatter heterogeneity above the planetary boundary layer, unusual large-scale vertical backscatter heterogeneity above the planetary bouundary layer, unusual large-scale vertical backscatter structure in the upper troposphere and lower stratosphere, and differences in the spatial resolution, detection threshold, and noise estimation for the two lidars. ¿American Geophysical Union 1991