Here are provided working examples and tools to work with CALIPSO data.
In addition to the tools available here, sample read software that can also be obtained from
the NASA Langley ASDC.
These are IDL routines written specifically for each data product.
The following CALIOP data analysis examples are intended to provide basic guidance on the use of CALIOP
data and demonstrate methods to solve particular problems. This does not guarantee that these are the only
methods or are the best methods. The accompanying codes are provided without support and should not be used
verbatim for publication-quality analyses.
Generate mean extinction profile
This is an example of how to generate a profile of mean extinction from the CALIPSO level 2 aerosol profile products
using basic quality screening techniques. The figures below shows the mean aerosol extinction profile and the relative
uncertainty without quality screening in blue and with quality screening in red.
Mean extinction with screened and unscreened data.
Relative extinction uncertainty with screened and unscreened data.
This example demonstrates how to create a histogram of CALIPSO feature optical depths from the level 2
aerosol layer products. It shows how to use the Feature_Classification_Flags to extract only dust aerosols
and how to apply basic quality screening with the Extinction_Uncertainty, CAD_Score, and ExtinctionQC flags.
The techniques demonstrated here can be used to compute statistics from other level 2 aerosol layer products.
The histogram it generates is shown below.
The follow source code modules or 'm' files are provide for those data users that use Matlab for
their data analysis.
For reading CALIPSO data files in an interactive mode, users on certain operating systems
(i.e. OS X) may simply drag the HDF file from their Finder or windows explorer window and onto
the Matlab command window. This action will automatically cause Matlab to open a new window where
you may select the science data set (SDS) to be loaded.
Alternatively you may type in 'hdftool' on the Matlab command line to manually open the hdftool
window and then select the file to open from the File->File Open, menu item.
To read in the altitude array that is contained in all CALIPSO lidar profile data products you
can use the following matlab commands. Note that the returned 'metadata' is a cell array, the second line converts
it to a normal array.
This provides a drop in replacement for the Matlab built-in function 'hdfread'. In older
versions of Matlab this function provided a significant performance increase over the
built-in function. Note that this function does not support the reading of VDATA.
Several of the following functions use readHDF.m, so you may be required to download it
if you want to try the examples.
This produces a vertical feature mask (vfm) image from the CALIPSO vfm data product
Feature_Classification_Flags. Users may select to display any one of the bit fields in
the classification flags. Below are shown two examples of images.
This produces a color modulated image of attenuated backscatter from the CALIPSO lidar level 1
data product data set Total_Attenuated_Backscatter_532. The images produced are similar to what
are available on the
CALIPSO browse image web site.
The color scale used on these images and the ones on the browse image website are nearly
This function creates an image of attenuated color ratio from the CALIPSO lidar level 1 data product, similar
to images available on the CALIPSO browse image web site. Attenuated color ratio is the ratio of
Attenuated_Backscatter_1064 to Total_Attenuated_Backscatter_532. The function subsets the level 1 data
file by user defined latitude limits and averages a user defined number of profiles together prior to
creating the color ratio. For reference, 15 profiles are averaged at a time for images on the CALIPSO
browse image web site. Here is an example of a color ratio figure generated by this function.
It shows a strong smoke layer over Africa on August 2nd 2007 @ 23:57Z.
This function creates an image of attenuated depolarization ratio from the CALIPSO lidar level 1 data product,
similar to images available on the CALIPSO browse image web site. Attenuated depolarization ratio is the
ratio of Perpendicular_Attenuated_Backscatter_532 to Total_Attenuated_Backscatter_532.
The function subsets the level 1 data file by user defined latitude limits and averages
a user defined number of profiles together prior to creating the color ratio. Here is an
example of a depolarization ratio figure generated by this function. It highlights some dust
aerosol along with some cirrus clouds over Africa on August 2nd 2007.
This Matlab GUI function allows you to plot and gain geolocation and temporal information from
CALIPSO level 1 or level 2 file. It may be particularly useful for determining the time that
the CALIPSO lidar passed overhead of a specific location.
Once the GUI is running, data files may be loaded by selecting the 'Open..' from the 'File'
pull-down menu. After the file is loaded, moving the slider underneath the 'Point Data' will move
a red colored dot along the lidar ground track. The time and lat, lon information in the 'Point Info'
windows correspond to the plotted point.
Additionally specific times may be searched for by entering the time of interest in the time
windows in the 'Find' box. Once the time has been entered click on the 'Time' button to calculate
the index of the time interval of interest. Clicking on the 'Copy' button will copy the index data
to the top-most input box. If you then click on the 'Update' button this will update the ground track.