Ozone Vertical Distributions from UV/Vis-Nadirspectra: Optimisation and Sensitivity Studies for the Use of the Long-Term Series of GOME-Measurements

The stratospheric ozone layer protects the biosphere from the effects of harmful ultraviolet radiation and is responsible for the temperature structure of the stratosphere. The severe changes of the ozone layer during the last decades clarified the need to monitor the variation of ozone concentrations.The Global Ozone Monitoring Experiment (GOME) which was launched in April 1995 onboard ESA´s second European Remote Sensing Satellite (ERS-2) enables us to investigate height resolved ozone distributions. The grating spectrometer measures direct and backscattered radiances in the ultraviolet and visible spectral range. The inversion algorithm FURM (FUll Retrieval Method) was developed to retrieve ozone vertical distributions from these spectral data using an Advanced Optimal Estimation approach.Internal broadband calibration corrections in the former standard versions of the FURM algorithm were forced by the increasing degradation of the optical components of GOME. Additional observed high frequency structures that inhibited the use of wavelengths below 290 nm resulted in a very weak stratospheric sensitivity above 35 km. Especially the profile retrieval in the low latitude range was affected by these deficiencies and motivated the development of a new calibration correction. The promising results encouraged further investigations of the higher latitude range. Here an additional modification of the broadband calibration correction is required to account for the low differential structure of ozone. Therefore a second approach is developed which leads in combination with the low latitude method to a significantly improved stratospheric ozone profile retrieval. These results make it now possible to investigate tropospheric ozone absorption structures which are otherwise dominated by any remaining stratospheric ozone feature. For the first time this new retrieval algorithm can now be used to retrieve longterm trends of ozone profiles on a global scale