Ratio of combined-channel to molecular channel image obtianed on March 18, 2003 as part of initial overnight operation tests. Values are approximate because calibration software was not complete at this time. Note cirrus cloud between altitudes of 9 an 10.5 km and a fog layer below 1.5 km. Fog is becoming optically thick near the end of the record.
Bulk depolarization image obtained on March 18, 2003 as part of initial overnight operation tests. Values are approximate because calibration software was not complete at this time.
Ratio of combined-channel to molecular channel image obtained on 05-Feb-03 showing ice crystal virga falling from a low-altitude water cloud. Values are proportional to the scattering ratio--however this data was obtained while testing an experimental I2 filter and is not precisely calibrated.
Our first observation of lidar returns with both the combined aerosol-molecular channel(green) and the I2 filtered channel(red). A cirrus cloud is seen between 10.5 and 12.5 km. These profiles are corrected for the inverse range-squared decay with the background subtracted but without any other processing.
Combined (green) and molecular (red) signals with the molecular scattering cross section profile (blue) computed from the 12 UTC Jan 8 Green Bay Wisconsin radiosonde profile. Signals have been normalized to the cross section profile below the cloud. A scaled version of the molecular cross section profile (black) has been normalized to the molecular return above the cloud. The ratio of the two molecular profiles provides a measurement of the cloud optical depth (tau=0.36 in this case). An enlargement of the figure can be viewed by clicking on the image. These are raw signals--no mathematical seperation of molecular and aerosol signals have been preformed and thus a slight feed through of the aerosol signal can be seen into the molecular signal inside the cloud.
The ratio of the combined channel signal to the I2 filtered signal for the profiles shown above. The profile was multiplied by 1.7 to yield a ratio of 1 in the clear air outside of the cloud. Outside of the cloud the air was exceptionally free of aerosols. The small dip below 1 for the scattering ratio below 2 km has been traced to a detector focusing error--this has been corrected. As expected a slight increase of the ratio with range is visible in clear air ( note the range between 4 and 19 km excluding the cloud). This is due to the dependence of the Doppler broadening on temperature. Lower temperature decreases the spectral width of the molecular backscatter and thus reduces transmission through the I2 filter. In operation, the system calibration coefficients are computed using an independently supplied temperature profile to account for this effect.