The DC-8 aircraft carried two ozone measuring instruments on PEM Tropics. The in situ instrument used the Nitrogen Ozone Chemiluminescence technique, recording data at a rate of 2 Hz. The remote instrument used the Differential Absorption Lidar (DIAL) technique with a pulse repetition rate of 30 Hz.
This intercomparison study took advantage of the fact that flight tracks were chosen to overfly a point on the ground (called a spiral point), allowing the Lidar to produce a vertical profile. Subsequently, the aircraft spiraled over the point allowing the in situ instrument to measure a vertical profile. In addition to spirals, intercomparisons were made when the aircraft ramped up or down. In the ramp cases, the geographic location of the in situ measurements varied more widely than that of the spiral cases. The Lidar vertical profile was chosen at some point in the ramp, and the in situ vertical profile was collected throughout the ramp. Details of the geographic locations and times are given on the line plots for each intercomparison.
The intercomparison was made by first determining the geometric altitude of the aircraft at each data point of both remote and in situ data. Both data sets were subsampled every 30 meters. The vertical resolution of the Lidar data is 400 meters. In order to match that, the subsampled in situ data were boxcar smoothed vertically to 390 meters. The horizontal resolution of the Lidar data is approximately 70 km, whereas that of each in situ data point is 115 meters.
The intercomparison profiles are archived on the GTE PEM Tropics archive under file names OZI*.PMT and can also be viewed on this WWW page within each set of flight data where appropiate.
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