A couple more RGB observations this week…

Ok, while I have a mintue I thought I’d make another post on observations with RGB imagery in the past few days.  The first image below is essentially a followup to Brian Guyer’s excellent post on the 24th.

Figure 1. MODIS RGB Nighttime Microphysics image valid May 24, 2012 at 0835Z. The burn area appears as the red “heart-shaped” area in SW New Mexico.

I wondered what the Nighttime Microphysics RGB would show for this burn area, given the heavy use of the 10.8 µm channel in this product’s “recipe”.   Notice the burn scar shows quite well, and is the pink, nearly heart-shaped area to the NW of KSVC.  This image was taken by the MODIS sensor at approximately 0835Z, or 0235 local (MDT).  I’ll have to admit I was a little perplexed, as I expected this area to be warmer than the surrounding terrain.  However, the apparent decrease in blue contribution in this area (the blue in the RGB “recipe” corresponds to the 10.8 um channel) would indicate a relatively colder surface.  Perhaps one of you folks with either more experience with RGBs or satellite detection of fires could help here.

Now, for a change as I take a look at another fog example…this time from my own forecast area (HUN).  The first image below is the MODIS RGB Nighttime Microphysics image valid May 23rd at 0340Z (1040 local CDT).

Figure 2. MODIS RGB Nighttime Microphysics image valid May 23, 2012 at 0340Z.

At first it may be a little difficult to see, but notice the aqua colors that show up in the extreme NE part of AL, but mainly in portions of southern Tennessee that are highlighted by the yellow circles.  This color in the Nighttime RGB imagery is typically indicative of the presence of fog and/or low clouds.  The southern circle represents the narrow valley locations along and near the Tennessee River, while the nothern circle represents fog and low clouds in the narrow Sequatchie Valley.  This valley area often acts as a region of local cool air production and the development of early fog.  As the cool air flows southward and gradually downhill along the TN River channel, fog development will spread into Jackson County.  The RGB image below, shows the relatively early development of fog in these critical areas.  However, notice the presence of slightly deeper convective clouds in the area, as indicated by the more yellow and tan colors.  An upper low was still exiting the area and lapse rates above the developing nocturnal inversion were enough to generate the convective clouds.  In the standard 11-3.9 um imagery below, it is nearly impossible to distinguish between the convective (but still fairly shallow) clouds and the low clouds/fog.

Figure 3. GOES-MODIS hybrid valid May 23, 2012 at 0345Z.

The RGB imagery here shows great utility in detecting fog under these difficult circumstances.  The next RGB image below shows the eventual development of fog that morning by 0800Z.  Here, the fog can be seen to have clearly spread throughout the valley areas of Jackson County (northeasternmost county in AL).  The Scottsoboro observation indicated visibilities below one quarter mile at this point.

Figure 4. MODIS RGB Nighttime Microphysics image valid May 23, 2012 at 0752Z. The aqua colors in NE Alabama, southern TN, and NW Georgia indicate fog/low clouds that have spread rapidly through valley areas overnight.

Here again, the RGB imagery show superior utility in the early detection of fog over traditional imagery that can have benefit to operations.

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