Favorable Conditions for the VIIRS Day-Night Band Reflectance

A big push for the VIIRS Front Range collaboration is to evaluate the VIIRS day-night band products as part of a JPSS Proving Ground evaluation.  In the overnight hours of July 21, the conditions were favorable to use the reflectance product (using reflected moonlight) which requires both a near full moon as well as the moon being over the horizon.  There were several interesting features to observe with the VIIRS overpass at 0821 UTC on 21 July in and around the Boulder and Cheyenne county warning areas.  Figure 1 kicks off with the VIIRS reflectance product.  The conditions were very favorable for using the reflectance product (just one day before the full moon and the moon was over the horizon) and provides a nighttime display of the region with almost visible imagery quality.  Since the day-night band is a low-light sensor, it also observes lights from cities (Denver and Cheyenne are pointed out).  This image also shows some shadows cast by the clouds.  Also, there is an interesting curved cloud feature in eastern Colorado and into western Kansas, circled in yellow.

refl_annotated

I wanted to compare the reflectance product to the high-resolution IR imagery in Figure 2.  The coldest tops in the northeast show up very well.  The circled feature further south does not show up, supporting that this feature is a low-level feature.

ir_annotated

To further investigate this we can use the VIIRS radiance RGB composite in Figure 3.  Here, a couple features stand out.  First, given the favorable conditions with the moon, the RGB is more useful in identifying low and high clouds compared to several nights ago.  In this image, the blue clouds are the highest clouds, which correspond well to the coldest tops seen in the IR.  Also, the interesting cloud feature circled stands out in yellow, signifying a low cloud feature.  Again, the city lights are seen in this channel and appear yellow.  Also, a feature that Rob Cox (SOO – Cheyenne) pointed out in an evaluation a few days ago, several lightning flashes are observed.  I attempted to see if the Colorado Lightning Mapping Array observed the flashes, but this was too distant from the network.

radrgb_annotated

Lastly, in Figure 4, we go back to the nighttime microphysics RGB which helps reinforce what we have been observing earlier.  The thick, high clouds discussed earlier show up as red, while the interesting feature circled stands out clearly as low clouds as shown by the radiance RGB as well.  Also, another small low cloud feature is seen coming off the storm system in the northeast, which may be a developing outflow.

ntmicro_annotated

8 thoughts on “Favorable Conditions for the VIIRS Day-Night Band Reflectance

  1. Very interesting to determine possible outflow boundaries. Let’s keep an eye out for those boundaries…..may be important in other severe weather events. Were low low clouds in the yellow oval observed by any other means?

  2. Hello Bill. Yes, this was very interesting with the outflow boundary. It was good timing with the VIIRS overpass, but this is what we can do with the extra channels on GOES-R. I believe there was another outflow a few days earlier as well, although the day-night band was not as favorable due to the lunar orientation. I can check to see if the 3.9 micro observed these clouds as well as look back into the METAR reports.

  3. Thanks Geoffrey. This is a stellar case. We have observed similar outflow boundaries from convection over NM in the past. We also have seen in cloud flashes on a couple VIIRS reflectance products this past month but they are well outside any LMA networks. The NT microphysics products is probably one of the most valuable in my opinion.

  4. Great discussion Geoffrey! Those interesting curved clouds you pointed out also were thunderstorm outflow boundaries that stemmed from the convection that moved through Southern Nebraska and Northern Kansas earlier that night, according to the standard GOES Imagery. Those outflow boundaries have a similar appearance to gravity waves.

  5. I appreciate the feedback nwsabq and wfocys. This was a very interesting case with a lot of activity occurring. Being the lightning person, I was hoping to get some Colorado Lightning Mapping Array observations, but it was just a tad too far. I agree with nwsabq that the nighttime microphysics is really demonstrating its worth. The additional insight is greatly appreciated wfocys! It will be interesting if we can capture some gravity waves as well for comparison down the road.

  6. Scott, thanks for the correct terminology! This particular feature really stood out, particularly in the nighttime microphysics. Also, I appreciate the additional example of the undular bore.

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s