Post on 15-Jan-2016
description
SEVIRI Height Retrieval Comparison with CALIPSO
Mike Pavolonis (NOAA/NESDIS)
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.
• 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.
May 6, 2010 (14:00 UTC)
Ash cloud
May 6, 2010 (14:00 UTC)
White: GOES-R Heights
Ash cloud
Ash cloud
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.
May 7, 2010 (03:00 UTC)
Ash clouds
May 7, 2010 (03:00 UTC)
Ash clouds
White: GOES-R Heights
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.
May 7, 2010 (14:00 UTC)
Ash clouds
May 7, 2010 (14:00 UTC)
Ash clouds
White: GOES-R Heights
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
May 8, 2010 (04:00 UTC)
Ash clouds
May 8, 2010 (04:00 UTC)
Ash clouds
White: GOES-R Heights
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.
May 8, 2010 (15:00 UTC)
Ash clouds
May 8, 2010 (15:00 UTC)
Ash clouds
White: GOES-R Heights
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.