October 21, 2010 Page 1 of 7
Generating a profile of mean CALIPSO aerosol extinction: an example of
basic quality screening techniques for CALIPSO level 2 profile extinction
products using MATLAB
In this example we demonstrate how to generate a vertical profile of mean extinction from the
CALIPSO level 2 profile products with some basic data quality screening. The process of averaging
extinction profiles is quite straight forward. However, applying the CALIPSO profile descriptive flags
for quality screening is a bit tricky because they are stored in a three dimensional array while
extinction coefficients are stored in a two dimensional array. More on this later… Since it is important
to pay attention to these flags, this document provides a practical example of how to apply profile
descriptive flags to screen extinction data.
The case we will use to demonstrate this process was acquired April 17, 2010 at about 20Z, shown in
Figure 1 below. The CALIPSO total attenuated backscatter measurements reveal an aerosol layer over
India extending from the Ganges Valley near Kathmandu (left) to the Bay of Bengal, just south of
Vishakhapatnam (right). The vertical feature mask in Figure 1b shows that CALIPSO level 2 algorithms
have detected this aerosol layer from about 5 km in altitude to the surface. We will use this case to
demonstrate how to compute a vertical profile of mean extinction with basic quality screening.
The MATLAB code and associated sample data that accompanies this example can be downloaded as
a zip file from the Tools section of the CALIPSO Data User’s Guide. Please unzip the .mat files and .hdf
file to your active MATLAB directory to follow along. The main function is called
quality_screen_CALIPSO_profile_products.m.
Figure 1. (a) CALIPSO total attenuated backscatter in km
-1
sr
-1
and (b) level 2 vertical feature mask of
feature type for an aerosol layer over India on April 17
th
, 2010.
(a) (b)
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