1. Tangent height offsets estimated by correlation analysis of ground-based data with O 3 limb profiles J.A.E. van Gijsel Y.J. Meijer

2. Overview Introduction –Data description Methodology –Visual analysis versus statistical analysis –Example of statistical analysis Results –ESA OL 3.0 and IFE 1.63 Limb ozone profiles A-priori profiles

3. Introduction Validation of SCIAMACHY limb ozone profiles with collocated ground-based measurements Detection and analysis of altitude offset Need for objective method to deal with biases

4. Datasets ESA OL 3.0 O 3 limb profiles IFE 1.63 O 3 limb profiles –Both based on ESA level 1 products Collocated ground-based observations: –Lidar –Sonde –Microwave (used for IFE 1.63 only)

5. Datasets II ESA OL 3.0: 454 collocated profiles –332 lidar ozone profiles –112 sonde ozone profiles IFE 1.63: 2346 collocated profiles –153 unique lidar ozone profiles –313 unique sonde ozone profiles –151 unique microwave ozone profiles

6. Methodology Splining of data points to obtain a common altitude grid Iterative shifting of the SCIA retrieved limb profiles for the correlation analysis (-5 to +5 km with steps of 200 m) Calculation of correlation coefficient between SCIA retrieval and collocated observation over altitude range 20 - 35 km Optimal altitude shift can be found at maximum correlation after all iterations

7. Uncertainties in methodology Chosen altitude range can influence results –Reliability of (collocated) instrument varies with altitude: ESA OL 3.0 lower ‘trust’ limit set to 20 km ESA OL 3.0 has a reference height of 40 km where relative error becomes very high Sonde data becomes less reliable over 30 – 35 km Interpolation over large intervals –For instance microwave data Differences in time/space between collocated measurements

8. Methodology II

9. Results: ESA OL 3.0 A-priori Mean optimal shift is close to 0. Spread increases towards the poles (as expected).

10. ESA OL 3.0 Limb Optimal altitude shift = 1.04 km downwards Standard deviation has decreased with respect to a- priori

11. Mean optimal altitude shift using microwave data strongly deviates from lidar & sonde. Microwave data have a low resolution and the registration of altitude is not very accurate, therefore they will not be further considered IFE 1.63 A-priori LidarSondeMicrowave 160 m-283 m947 m

12. IFE 1.63 A-priori II AllWestCentral- West Central- East East -178 m-79 m-161 m-212 m-273 m Dependency on state position due to differences in latitude

13. IFE lidar+sonde limb

14. IFE 1.63 Limb Mean optimal shift (based on lidar+sonde) = 1.17 km (1.04 km for ESA OL 3.0) Difference between East and West for a-priori was ±200 m AllWestC.-WestC.-EastEast Lidar-966-810-941-986-1132 Sonde-1281-1133-1174-1338-1522 Microwave-437-265-352-478-727 Distances in table in meters

15. 4 profiles within state

16. Summary The ESA OL 3.0 and the IFE 1.63 O 3 limb profiles have been validated using ground-based O 3 data –Visual analysis Not objective –Statistical analysis Offsets:ESA OL 3.0:1.04 Km IFE 1.63:1.17 Km Ground-based data should be inter-compared to ensure quality

17. Questions? Thank you for your attention !

18. IFE Microwave limb