Day-Night Band Observations from Jan 12th…

Just thought I’d make a short post to mention a myriad of features observed in the early morning hours of the 12th from the VIIRS instrument aboard the Suomi NPP satellite.  In image 1 below, a faint surface snow field can be seen stretching across parts of northwestern Missouri into Iowa, deep convective clouds and even a couple of flashes of lightning were present in the western Atlantic off the North Carolina coast, and rippling wave clouds can be seen in the lee of the Appalachians.  These were among several features I wanted to showcase, and importantly, the surface snow field and lightning are two features observable only in the Day-Night Band.  However, I also wanted to point out an unusual and rather sharp reflectance that appeared in the near coastal waters of Louisiana.  In fact, it’s probably the most prominent feature in the image.  In image 1 below, notice the bright yellow colors that appear in the Gulf waters just south of Louisiana.

Image 1.  Soumi NPP VIIRS Day-Night Band Radiance RGB, valid 12 Jan 2014 0700 UTC

Image 1. Soumi NPP VIIRS Day-Night Band Radiance RGB, valid 12 Jan 2014 0700 UTC

This image is the Radiance RGB produced from the raw image of emitted and reflected light.  There is likely no source emitting that much light south of Louisiana, so this is largely reflected light.  But, what is doing the reflecting?  Also, why was there such a sharp gradient in the reflected light?  At the time of the Suomi NPP passage, the moon was at an elevation of about 35.5 degrees above the western horizon (at New Orleans, courtesy of the U.S. Naval Observatory).  So, the moon wasn’t behind the satellite during its passage, resulting in some glare from directly reflected light, but was relatively low on the horizon to its left (from the point of view facing Earth).  I don’t really have any answers, but wanted to point out this odd feature in case someone else had any good ideas.

For the previous day, I noticed that winds in the region had been southwesterly, but then shifted from the west to northwest by the aftenoon as a cold front crossed the area.  Offshore winds dominated for the rest of the day and were gusty at times before calm winds prevailed late that night.  Perhaps some material of a more reflective property upwelled during the afternoon and evening?  Or perhaps there was something about the thermal properties of the water that resulted in refraction of light into the sensor?  Without a more thorough analysis I can’t be sure.  I don’t recall seeing anything like this in the Day-Night Band imagery before.  Notice the area of brightness appears in the Day-Night Band Reflectance product quite well too (image 2).


Image 2. Soumi NPP VIIRS Day-Night Band Reflectance image, valid 12 Jan 2014 0700 UTC

3 thoughts on “Day-Night Band Observations from Jan 12th…

  1. Wow, great post, which asks a great question! My guess is that water runoff was high, given the amount of precip the lower Mississippi River Valley had recently received: ; this runoff transported a great deal of sediment out into the near-shore waters, which sort of showed up in an AWIPS image of MODIS visible channel data on 14 January (but does not appear to have a direct 1:1 influence on the entire MODIS SST pattern): ; a better answer might be gleaned from true-color MODIS and VIIRS RGB images from 14 January, viewed using the SSEC RealEarth web map server: ; the different character of sediment and/or algal blooms may have had differing reflective properties, which might explain the sharp gradient in the bright-vs-dark seen in your 12 January VIIRS DNB image. Pure conjecture on my part though!

  2. Thanks for the thorough comment Scott! I think tha’ts a good guess. I noticed the apparent increased sediment in MODIS true color imagery later that day (12th). However, the sediment still seems rather “robust” along the LA coast (, but there was no similar bright reflectance this morning appearing in the Day-Night Band. Perhaps there was something different about the properties of the sediment the other day vs yesterday/last night? Of course, all else is not equal, with differences in the Moon-Earth-satellite geometry from the 12th to today (if that is a factor).

  3. Yes, the Moon-Earth-Satellite geometry is certainly a big player here: you would not expect to see that same glint pattern over the same location on consecutive days. Said geometry happened to be just right on 12 January to allow you to see that particularly interesting glint gradient over the coastal waters.

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