Validation of ACHA on AVHRR with CALIPSO/CALIOP

This page present an analysis of the  AWG Cloud Height Algorithm (ACHA) applied to the 11 and 12 micron channels of the AVHRR.

The reference of this approach is given by Heidinger and Pavolonis (2009). Though elements of this approach have changed, the basic physics and approach are the same today and are consistent with the approaches applied to other channels on other sensors.

This analysis shows a comparison of one day of AVHRR against CALIPSO/CALIOP. Note, AVHRR and CALIPSO colocations do not occur evenly over the globe and the location and amount varies from day to day.  This day was chosen as it represented a large number of CALIPSO/NOAA-18 colocations.


AVHRR data:  NOAA-18 from August 6, 2006.
CALIPSO data: CALIOP 1 km Cloud Layer Product from the same day.

The time threshold used in this analysis is 30 minutes.

The CALIPSO/CALIOP cloud top height for comparison was computed as the mean cloud altitude of the highest cloud layer in the column.

In the following plots, ACTIVE = CALIPSO/CALIOP, PASSIVE = ACHA on AVHRR


Global View of Passive Results of Cloud-top Temperature for this day's ascending node data
ascending data




Global View of Passive Results of Cloud-top Temperature for this day's descending node data
descending data





Scatterplot of cloud-top height values

scatterplot



Comparison of the distribution of cloud-top height from CALIPSO and AVHRR


cth distribution comparison



Distribution of Cloud-top Height Differences

cth difference distribution



Orbit Node Images (ASC = ascending or day, DES = descending or night)

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