8.1. Executing the VIIRS Polar2Grid Test Case

To run the VIIRS GeoTIFF test case, unpack the test data as shown in Section 2.2 and execute the following commands:

cd polar2grid_test/viirs
mkdir work
cd work
polar2grid.sh -r viirs_sdr -w geotiff -p true_color false_color --grid-configs \
  ${POLAR2GRID_HOME}/grid_configs/grid_example.yaml -g miami --weight-distance-max 1 -f ../input

The test case consists of 6 input direct broadcast HDF 5 SDR granules for a selection of VIIRS bands from a pass acquired on 19 March 2017 at 18:32 UTC. In this test, the Polar2Grid software is using the example configuration file (${POLAR2GRID_HOME}/grid_configs/grid_example.yaml) and the lambert conformal conic (lcc) miami grid definition entry located within it. We will create one true and one false color image at 300 m resolution, 750 lines x 1000 elements centered on the US city of Miami in the state of Florida.

The creation of the true and false color images includes the Atmospheric Rayleigh Scattering Correction, and sharpening of the image to the spatial resolution of the VIIRS I-Bands. We are using a --weight-distance-max option of 1 to inform the elliptical weight averaging (EWA) technique how to weight the effect of the input pixel to an output pixel based upon its location in the scan line and other calculated coefficients. Although this may result in the “sharpest” output resolution image, the user should be aware that with reprojecting VIIRS terrain corrected imagery this may lead to black missing data sections in regions of varying terrains, especially at higher view angles. That is why the default --weight-distance-max value is 2.

The processing should run in less than 2 minutes and create 2 atmospherically corrected and sharpened output VIIRS GeoTIFF true and false color images.

If the VIIRS Polar2Grid processing script runs normally, it will return a status code equal to zero. If the VIIRS Polar2Grid processing script encounters a fatal error, it will return a non-zero status code.

To verify your output files against the output files created at UW/SSEC, execute the following commands:

cd ..
p2g_compare.sh output work

This script compares the values of all bands in the GeoTIFF file for the true and false color high resolution images. The verification text string from our test system is shown below.

p2g_compare.sh output work

Comparing work/npp_viirs_false_color_20170319_183246_miami.tif to known valid file
INFO:__main__:Comparing 'work/npp_viirs_false_color_20170319_183246_miami.tif' to known valid file 'output/npp_viirs_false_color_20170319_183246_miami.tif'.
INFO:__main__:0 pixels out of 3000000 pixels are different
INFO:__main__:Comparing 'work/npp_viirs_true_color_20170319_183246_miami.tif' to known valid file 'output/npp_viirs_true_color_20170319_183246_miami.tif'.
INFO:__main__:0 pixels out of 3000000 pixels are different
All files passed
SUCCESS

The VIIRS true color GeoTIFF image created from the test data is displayed below:

../_images/npp_viirs_true_color_20170319_183246_miami.jpg

Fig. 8.1 GeoTIFF true color image created from the 19 March 2017 VIIRS test data centered on Miami, Florida.