1. SEVIRI Height Retrieval Comparison with CALIPSO Mike Pavolonis (NOAA/NESDIS)

2. Procedure The GOES-R volcanic ash retrieval ( http://cimss.ssec.wisc.edu/~mpav/GOESR_ABI_ATBD_Aviation_VolAsh_v2.1.pdf ) was applied to SEVIRI data. http://cimss.ssec.wisc.edu/~mpav/GOESR_ABI_ATBD_Aviation_VolAsh_v2.1.pdf CALIPSO (lidar) overpasses were matched in time and space to SEVIRI. Multi-spectral SEVIRI imagery was used to interpret the cloud layers identified by CALIPSO (e.g. only cases where it was obvious that CALIPSO over-passed a definitive ash signal in SEVIRI false color imagery were considered). The retrieved GOES-R ash cloud heights were overlaid on the lidar backscatter cross section (in white). To illustrate that the ash clouds are generally very optically thin, the heights that would be retrieved if the ash was assumed to be opaque to 11 um radiation are also overlaid (in magenta). The lidar backscatter data also indicate that the clouds are optically thin. Overall the GOES-R ash cloud heights (using SEVIRI as a proxy for GOES-R) compare very well to the lidar cloud top boundaries. The main exception is cloud edges, which is expected.

3. May 6, 2010 (14:00 UTC) Ash cloud

4. May 6, 2010 (14:00 UTC) White: GOES-R Heights Ash cloud

5. May 6, 2010 (14:00 UTC) White: GOES-R Heights Magenta: IR Window Heights The GOES-R ash cloud heights closely match the CALIPSO cloud top boundary. The traditional methodology underestimates the cloud height.

6. May 7, 2010 (03:00 UTC) Ash clouds

7. May 7, 2010 (03:00 UTC) Ash clouds White: GOES-R Heights

8. May 7, 2010 (03:00 UTC) Ash clouds White: GOES-R Heights Magenta: IR Window Heights The GOES-R cloud heights correctly capture the spatial pattern of ash cloud heights.

9. May 7, 2010 (14:00 UTC) Ash clouds

10. May 7, 2010 (14:00 UTC) Ash clouds White: GOES-R Heights

11. May 7, 2010 (14:00 UTC) Ash clouds Even though these clouds are very optically thin, the GOES-R ash cloud heights closely match the CALIPSO cloud top boundaries, unlike the IR window based height. White: GOES-R Heights Magenta: IR Window Heights

12. May 8, 2010 (04:00 UTC) Ash clouds

13. May 8, 2010 (04:00 UTC) Ash clouds White: GOES-R Heights

14. May 8, 2010 (04:00 UTC) Ash clouds White: GOES-R Heights Magenta: IR Window Heights Once again the GOES-R height retrieval is able to capture the considerable spatial variability of the ash cloud.

15. May 8, 2010 (15:00 UTC) Ash clouds

16. May 8, 2010 (15:00 UTC) Ash clouds White: GOES-R Heights

17. May 8, 2010 (15:00 UTC) Ash clouds White: GOES-R Heights Magenta: IR Window Heights In this example, CALIPSO just grazes the ash cloud visible in multi-spectral imagery. Thus, the IR measurements have limited sensitivity to the ash cloud height at the overpass location. Nevertheless, the map of ash cloud heights indicates that heights comparable to those indicated by CALIPSO are present very close to the CALIPSO overpass.