Intercomparison of the NIMBUS 7 SBUV/TOMS total ozone data sets with Dobson and M83 results

Abstract

Total ozone measurements made by the SBUV and TOMS instruments on the NIMBUS 7 spacecraft are compared with measurements from 62 Dobson and 18 M83 stations. On the average, TOMS ozone values are 6.6% smaller than Dobson and 9.1% smaller than M83; corresponding SBUV biases are 8.3% and 11.3%, respectively. Use of SBUV or TOMS as a transfer standard reveals an apparent bias between the Dobson and M83 networks of 3.0 or 2.5%respectively. Major portion of the bias between the space and ground measurements is attributed to uncertainties in the ozone absorption coefficients used in processing the measurements. Precision of total ozone retrieved from either the SBUV or the TOMS instrument is shown to be better than 2%, which is comparable to that of a well run Dobson station. Precision of a typical Dobson measurement is estimated at about 2% and that of an M83 measurement is estimated to be 4%. Apparent station to station biases of up to 11.2% for Dobson and 15.5% for M83 are shown. Daily and seasonal variations of ozone measured by the satellite over selected Dobson stations are found to be in excellent agreement with the ground observations. An instrumental drift is found in the SBUV/TOMS total ozone measurements that is essentially linear with time and has a rate of 0.5% per year for the first year of data. A better understanding of instrument changes is expected to help reduce any further drift.