Ozone differential absorption lidar algorithm intercomparison

An intercomparison of ozone differential absorption lidar algorithms was pe rformed in 1996 within the framework of the Network for the Detection of St ratospheric Changes (NDSC) lidar working group. The objective of this resea rch was mainly to test the differentiating techniques used by the various l idar teams involved in the NDSC for the calculation of the ozone number den sity from the lidar signals. The exercise consisted of processing synthetic lidar signals computed from simple Rayleigh scattering and three initial o zone profiles. Two of these profiles contained perturbations in the low and the high stratosphere to test the vertical resolution of the various algor ithms. For the unperturbed profiles the results of the simulations show the correct behavior of the lidar processing methods in the low and the middle stratosphere with biases of less than 1% with respect to the initial profi le to as high as 30 km in most cases. In the upper stratosphere, significan t biases reaching 10% at 45 km for most of the algorithms are obtained. Thi s bias is due to the decrease in the signal-to-noise ratio with altitude, w hich makes it necessary to increase the number of points of the derivative low-pass filter used for data processing. As a consequence the response of the various retrieval algorithms to perturbations in the ozone profile is m uch better in the lower stratosphere than in the higher range. These result s show the necessity of limiting the vertical smoothing in the ozone lidar retrieval algorithm and questions the ability of current lidar systems to d etect long-term ozone trends above 40 km. Otherwise the simulations show in general a correct estimation of the ozone profile random error and, as sho wn by the tests involving the perturbed ozone profiles, some inconsistency in the estimation of the vertical resolution among the lidar teams involved in this experiment. (C) 1999 Optical Society of America.