Creating a VIIRS brightness temperature difference field from direct broadcast data using McIDAS-V
This blog post contains Suomi-NPP VIIRS imagery that was derived (using CSPP) from data downloaded at the Direct Broadcast site at CIMSS. That blog post suggests the need of a brightness temperature difference field from the I04 and I05 data that can be found in this (https://ftp.ssec.wisc.edu/pub/eosdb/npp/viirs/2022_03_03_062_0632/sdr) direct broadcast directory (direct link, available for about 6 days). The Sensor Data Record directory includes I04 and I05 hdf5 granules that McIDAS-V can read: SVI04_npp_d20220303_t0641201_e0642443_b53613_c20220303071038095682_cspp_dev.h5 and SVI05_npp_d20220303_t0641201_e0642443_b53613_c20220303071039605225_cspp_dev.h5 ; determining exactly which granule you want — there are 10 different granules in this particular directory — is partly trial and error and partly viewing the orbit path (here) and choosing wisely. Save those files into a directory; also save the ‘GITCO’ files (that is: GITCO_npp_d20220303_t0641201_e0642443_b53613_c20220303070838040363_cspp_dev.h5) that contain georeferencing for the Imager (‘I’) bands (similarly, GMTCO files contain georeferencing for the Moderate-resolution ‘M’ bands).
After starting up McIDAS-V, you want to load the data. Note above that I’ve clicked on JPSS Imagery, and navigated to the directory containing the downloaded data (that directory also includes the GITCO files for those granules, but you don’t see them here). I’ve chosen both I04 and I05 data files from one granule, observed from 06:41:20.1 to 06:42:44.3. Click on ‘Add Source’ in the lower right corner of the window. If you then expand ‘IMAGE’ under ‘Fields’, you’ll see both I04 and I05 Brightness Temperatures.
Next, under the ‘Data Sources:’ tab, click on ‘Formulas’. You will see a ‘Miscellaneous’ tab, and under that tab, a ‘Simple Difference a-b’ choice. Choose that and click ‘Create Display’ — this will pop up a window in which you can choose the a (in this case, I05 Brightness Temperature) and b (for this case, I04 Brightness Temperature). Subsect the portion of the granule that you want to display using shift-left click and drag — and — after clicking ‘create image’ — you end up with the image below (zoomed in).
There is some fine-tuning yet to do. Under the ‘Legend’ in the image above, right-click on ‘VIIRS 2022-03-03…’ to bring up the Control Window shown below. Slide the ‘Texture Quality’ from ‘Medium’ to ‘High’ (if you have a large image — much larger than this one! — that will test your machine’s RAM!)
Similarly, if you right-click (again!) under ‘Legend’ and ‘VIIRS 2022-03-03…’ to ‘Edit->Properties’, you can change the Layer Label to include more information, which I did, as shown in the image below. Finally, I edited the color table to highlight positive values (that is, where I05 – I04 Brightness Temperature Difference is between 0 and 2o C) that might show where stratiform clouds are present. That result is shown below. Yellow in the enhancement shows no difference between the fields, blue is a brightness temperature difference of 2o C. Are you obtaining a good signal of fog in the region of the very dense fog over southern Volusia County? I’d only ask what a ‘good signal’ is!