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Archive for the ‘VIIRS’ Category

I’ve written about the operational utility of Day-Night Band (DNB) RGB imagery several times in the SPoRT blog, and here I’m going to take the chance to do that again.  First, just some brief background information in case you’re not familiar with this type of imagery.  The DNB RGB is composed of a long wave IR channel (~10.8 µm), which is assigned to the blue color component of the RGB recipe, while the DNB channel (0.7 µm) is assigned equally to the red/green colors of the RGB.  SPoRT produces two DNB RGB products: Radiance and Reflectance.  I typically prefer the Radiance RGB for operational uses since it is composed of the raw data (emitted and reflected light) from the sensor.  Sure, cities are quite bright in the imagery, but the cloud features also stand out better compared to the reflectance product, where the data are normalized by the available amount of moonlight. Below are a few observations from the Suomi-NPP VIIRS instrument during this most recent full moon cycle.

First, take a look at the images below from the SE half of the CONUS on the early morning of December 7th.  The top image (Image 1) is a Nighttime Microphysics RGB at approx. 0736 UTC, while Image 2 is a DNB Radiance RGB valid at the same time.  While this type of imagery is far superior to legacy IR imagery (even enhanced with fanciful color curves), there are proper operational forecasting/analysis applications that one has to consider.  The Nighttime Microphysics RGB is generally more useful for distinguishing different cloud types (e.g., low stratus vs fog, thin cirrus vs thick cirrus, etc).  After at least a year of viewing the DNB imagery, I think perhaps the best application of these types of imagery (at least with respect to operational forecasting) lies in the ability to view low clouds through cirrus at night.  No other imagery available to forecasters offers this capability currently.  Take for example these first two images below and pay close attention to the cloudy regions stretching from the central Plains into the lower Mississippi Valley.

Image 1.  Nighttime Microphysics RGB 0736 UTC 7 Dec 2014

Image 1. Nighttime Microphysics RGB 0736 UTC 7 Dec 2014.  Ceiling and Visibility observations from some ASOS and AWOS stations also shown in cyan.

Suomi-NPP VIIRS Day-Night Band Radiance RGB 0736 UTC 7 Dec 2014.  Ceiling/Visibility observations are shown in cyan.  Notice that details of the extensive deck of low clouds can be seen more easily than in the Nighttime Microphysics RGB.

Image 2.  Suomi-NPP VIIRS Day-Night Band Radiance RGB 0736 UTC 7 Dec 2014. Ceiling/Visibility observations are shown in cyan. Notice that details of the extensive deck of low clouds can be seen more easily than in the Nighttime Microphysics RGB.

Notice that in the Nighttime Microphysics RGB the expansive deck of low stratus across much of Kansas, southwestern Missouri and Oklahoma is almost entirely obscured by the cold cirrus clouds.  Of course, this is only realized upon looking at the DNB imagery.  Details in the low stratus can also be observed in the DNB imagery, such as the cloud banding stretching SW-NE across much of northern Louisiana and Mississippi.  Since the cloud bases in this imagery were mostly at MVFR and IFR levels with respect to aviation forecast concerns, knowledge about the details and characteristics of the low clouds are very important.

The next series of images from the New England region in the early morning hours of December 9th again demonstrates this application of the DNB imagery.

Image 3.  Suomi-NPP VIIRS IR (~10.8 u m) 0658 UTC 9 Dec 2014.  Ceiling/visibility observations from regional ASOS/AWPS are shown in cyan.

Image 3. Suomi-NPP VIIRS IR (~10.8 µm) 0658 UTC 9 Dec 2014. Ceiling/visibility observations from regional ASOS/AWPS are shown in cyan.

Image 4.  VIIRS Nighttime Microphysics RGB 0658 UTC 9 Dec 2014.  Ceiling/visibility observations shown in cyan.

Image 4. VIIRS Nighttime Microphysics RGB 0658 UTC 9 Dec 2014. Ceiling/visibility observations shown in cyan.

Image 5.  VIIRS DNB Radiance RGB 0658 UTC 9 Dec 2014.  Ceiling/visibility observations shown in cyan.

Image 5. VIIRS DNB Radiance RGB 0658 UTC 9 Dec 2014. Ceiling/visibility observations shown in cyan.

In the images above, notice that the extensive low cloud deck across the region that spans from Maine to at least as far south as northeastern North Carolina cannot readily be observed either in the legacy IR (10.8 µm ) imagery or in the Nighttime Microphysics RGB.  However, more details about the low clouds can be discerned from the DNB imagery.  Sure, cirrus clouds are optically thick enough to prevent viewing of any low clouds in the NY metro area.  Nevertheless, the advantages of the DNB imagery for detecting low clouds beneath thin cirrus can clearly be seen.  Again, as expressed earlier, this type of imagery certainly offers application for aviation forecasting, in particular.

Lastly, here are some observations from just this morning (Dec 10th) over the Rio Grande Valley region.

VIIRS color-enhanced IR (10.8 u m) image 0819 UTC 10 Dec 2014.  Ceiling/visibility observations are shown in cyan.

Image 6.  VIIRS color-enhanced IR (10.8 µm) image 0819 UTC 10 Dec 2014. Ceiling/visibility observations are shown in cyan.

Image 7.  VIIRS DNB Radiance RGB 0819 UTC 10 Dec 2014.  Ceiling/visibility observations are shown in cyan.

Image 7. VIIRS DNB Radiance RGB 0819 UTC 10 Dec 2014. Ceiling/visibility observations are shown in cyan.

In the VIIRS IR image (Image 6) just as in previous IR imagery the cirrus clouds obscure the presence of any clouds beneath.  However, the patchy low clouds in eastern New Mexico can be much more easily seen in the DNB imagery.  In the area between Midland, TX (KMAF) and Fort Stockton (KFST), a forecaster might have made the assumption that the low clouds were continuous based on the observations alone and without the aid of the DNB imagery.  Yet, what becomes noticeable in the DNB imagery is that a gap exists in the low cloud deck.

Of course, with all of this said, the availability of the imagery severely limits its application for operational forecasting and analysis.  Generally, only one or two passes are available over a given location on any night.  Also, due to moonlight limitations, the imagery are only available for about half of the month…at best.  I can only lament that the DNB imagery will not be available on a geo-stationary platform (at least anytime soon).  Nevertheless, understanding the limitations of the imagery while also appreciating its advantages can offer operational utility when applied properly to a forecast challenge.

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A unique weather event is unfolding this week as Hurricane Odile, now a tropical storm, is impacting Baja California Sur, bringing heavy rain and high winds to the region and causing tourists to evacuate resorts. The National Hurricane Center reports that Odile ties Olivia (1967) as the strongest hurricane to make landfall in the satellite era in Baja California Sur**. NASA SPoRT provides specialized satellite products to National Weather Service Forecast Offices as well as National Centers such as the National Hurricane Center to aid forecasting high impact events such as Hurricane Odile.

Below is an example of Passive Microwave RGB imagery created from the NASA Global Precipitation Measurement (GPM) mission as part of The Core Observatory satellite launched on 27 February 2014. The images are in N-AWIPS (National Centers for Environmental Prediction Advanced Weather Interactive Processing System) format and are an example of products available to forecasters at the National Hurricane Center.  Forecasters use the 89 GHz RGB product to look for areas of strong convection which show up as deep red as seen in Fig. 1 which captures Hurricane Odile a few hours before landfall.

89 GHz RGB 0121 UTC 15 September 2014. Areas of deep convection appear red and can be seen surrounding the eye wall and within the rainbands of Odile in this image a few hours before landfall.

Figure 1. GMI 89 GHz RGB 0121 UTC 15 September 2014. Areas of deep convection appear red and can be seen surrounding the eye and within the rainbands of Hurricane Odile in this image a few hours before landfall.

The 37 GHz can additionally be used to distinguish areas of deep cloudiness (light blue) from more active convection (pink) as well as open water (green) or land (cyan).  Note the areas of pink or active convective in Fig. 2 surrounding the eye and within the rainbands.

odile_37RGB1

Figure 2. GMI 37 GHz RGB 0121 UTC 15 September 2014. Areas of active convection appear pink and can be seen surrounding the eye and within the rainbands of Hurricane Odile in this image a few hours before landfall.

Figure 3 and 4 show similar observations from the legacy NASA Tropical Rainfall Measurement Mission (TRMM) as Hurricane Odile made landfall near Cabo San Lucas around 445 UTC 15 September. TRMM is expected to run out of fuel by February 2016 and will no longer be available to collect valuable observations. We are well prepared for a replacement with GPM in orbit and already collecting observations.

TRMM 89 GHz RGB 0307 UTC 15 September 2014

Figure 3. TRMM 89 GHz RGB 0307 UTC 15 September 2014.  Areas of deep convection appear red and can be seen surrounding the eye and within the rainbands of Hurricane Odile in this image a little over one hour before landfall.

TRMM 37 GHz RGB

Figure 4. TRMM 37 GHz RGB 0307 UTC 15 September 2014.  Areas of active convection appear pink and can be seen surrounding the eye and within the rainbands of Hurricane Odile in this image a little over one hour before landfall.

Additionally the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band Radiance imagery from the next generation NASA Suomi National Polar-orbiting Partnership (NPP) satellite shows an impressive picture of Hurricane Odile approximately one day before landfall (Fig. 5). Note the city lights that can be seen through the clouds in Fig. 5 as well as lightning within the area of convection in the rainband. This imagery can be used to support disaster response and help emergency managers identify the areas where conditions have caused power outages. Local knowledge of city light patterns can allow users to identify where the most significant power outages are and determine where to begin relief efforts.

VIIRS Day-Night Band Radiance

Figure 5. VIIRS Day-Night Band Radiance 0904 UTC 14 September 2014. City lights and lightning observed approximately one day before Hurricane Odile made landfall.

As the community transitions from legacy instruments such at TRMM and MODIS, NASA SPoRT will continue to develop unique products from Next-Generation missions such as GPM and Suomi NPP to aid National Weather Service Forecast Offices and National Centers in forecasting high impact events such as Hurricane Odile.

**see archived National Hurricane Center forecast discussion at http://www.nhc.noaa.gov/archive/2014/ep15/ep152014.discus.021.shtml?

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I didn’t have a chance to make this post last week when the imagery were more time-relevant.  Nevertheless, I wanted to point out another example of the usefulness of MODIS and VIIRS imagery over current GOES imagery and show the usefulness of exciting products and imagery to come!  First, let’s take a look at the color-enhanced GOES-IR image below from the morning (0715 UTC) of June 20th.

Color-enhanced GOES-IR (11um) image valid 0715 UTC 20 June 2014

Image 1.  Color-enhanced GOES-IR (11 µm) image valid 0715 UTC 20 June 2014

 

I’ve placed the yellow circles in the image for a reason, which you’ll see below.  Further down, I’m going to show areas of fog displayed in the MODIS and VIIRS imagery, and granted, this is not the standard GOES channel difference (11-3.9 µm) typically used for making fog assessments.   However, this post is meant to show current (MODIS / VIIRS) and future capabilities (GOES-R / JPSS) that will make fog detection and cloud differentiation much more easy for the operational forecaster.  So, in the image above, fog is nearly unidentifiable as it was in the 11-3.9 µm channel difference image that morning (not shown).  Mainly high cirrus clouds can be observed scattered across the region.  Now, let’s take a look at the MODIS “fog” product, or channel difference (11-3.9 um) product valid at about the same time (Image 2).

Color-enhanced MODIS 11-3.9 u m product valid 0718 UTC 20 June 2014

Image 2.  Color-enhanced MODIS 11-3.9 µm image valid 0718 UTC 20 June 2014

Notice that in the same areas we can now begin to see low clouds (indicated by yellow colors) scattered around the valleys of the southern Appalachian region.  While the GOES-East imager is capable of detecting larger scale fog often in the valleys in the eastern circle, fog in the valleys in the western circle present challenges for the current GOES-East instrument, and is often not shown very well (even in the standard 11-3.9 µm channel difference).    Next, let’s take a look at a VIIRS Nighttime Microphysics RGB valid at about the same time.

VIIRS Nighttime Microphysics RGB valid 0723 UTC 20 June 2014

Image 3.  VIIRS Nighttime Microphysics RGB valid 0723 UTC 20 June 2014

In the RGB imagery it is much easier to detect the extent of the fog, making the operational forecast process much more effective.  Notice also that it is possible to see the fog through the higher clouds around the TN/GA/NC border region.  Not only does the resolution of the VIIRS and MODIS instruments allow for superior fog detection, but the RGBs in particular offer tremendous operational advantages.  As a user of RGBs for about 2 years now, I am convinced that this type of imagery has a relevant and needed place in future operational forecasting.  Of course, it will take time for forecasters to become accustomed and adjust to the new imagery, but it will happen.

 

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This was one of those storms that people will talk about for years, especially those that were directly affected by it.  It all started with three separate shortwaves that all phased together once off the Mid-Atlantic coast, far enough offshore to limit any direct effects save for some unusual late season snow and gusty winds the next day.  The highest impact area included Cape Cod, Nantucket, Nova Scotia, and New Foundland.  I’m sure any ships that were in the vicinity were not happy with this situation!

GOES-Sounder RGB Air Mass animation valid 03/24/14-03/26/14.

GOES-Sounder RGB Air Mass animation valid 03/24/14-03/26/14.

The evolution of the nor’easter can be seen in the GOES Sounder RGB Air Mass animation above.  A southern stream system originating in the Gulf of Mexico moved east of Florida while two other shortwaves dropped southeast out of Canada.  All of the pieces combined near the North Carolina coastline, but the explosive deepening took place as the combined system moved northeast away from the Mid-Atlantic.  There appears to be a few stratospheric intrusions, but the most impressive intrusion occurs with the final shortwave as noted by the dark oranges and reds that appear at the end of the day on 03/25.  When models are forecasting a phasing situation, this product can be quite useful in identifying the features and observing the stratospheric drying seemingly “bleed” from one shortwave to the other.

MODIS RGB Air Mass product valid at 1540 UTC on 03/26/14.

MODIS RGB Air Mass product valid at 1540 UTC on 03/26/14.

MODIS RGB Air Mass product with ASCAT winds overlaid valid at 1540 UTC on 03/26/14.

MODIS RGB Air Mass product with ASCAT winds overlaid valid at 1540 UTC on 03/26/14.

The two MODIS RGB Air Mass products above show the nor’easter near peak intensity.  Notice how distinct the gradient between oranges and greens is in this image, almost as though you can see the upper portion of the frontogenesis, well behind the actual front.  The intensity of the stratospheric intrusion is quite evident by the dark pinks near the center of the cyclone.  The second image shows the wind field overlaid from ASCATB.  Notice the large area of hurricane force winds (red wind barbs) near the bent-back front, in the comma-head of the cyclone.  This area of wind affected parts of Southeast Massachusetts, including Nantucket where winds gusted from 60-85 mph.  Nantucket recorded a wind gust of 82 mph and about 10″ of snow.  Meanwhile, Nova Scotia bore the brunt of this beast with wind gusts of 129 mph at the Bay of Fundy and 115 mph in Wreckhouse.  Waves were equally impressive with altimeter readings between 40-50 ft and a buoy report of 52.5 ft.

GOES-13 Infrared imagery with the GLD-360 30-minute lightning density product overlaid.

GOES-13 Infrared imagery with the GLD-360 30-minute lightning density product overlaid.

Another interesting aspect of this storm was the two distinct areas of thunderstorms that erupted.  I overlaid the OPC and TAFB offshore zones for reference.  Notice well east of the Bahamas there are possible supercell thunderstorms associated with the southern shortwave energy.  Meanwhile, as the strong northern stream shortwaves exit the NC coastline, two areas of thunderstorms developed with the easternmost storm exhibiting supercell characteristics.  Although the lightning was not as intense with this northern area, I would speculate that the storms were associated with very strong wind gusts due to the dry air associated with the stratospheric intrusion.

VIIRS Visible image valid at 1719 UTC on 03/26/14.

VIIRS Visible image valid at 1719 UTC on 03/26/14.

VIIRS Visible image with the 18 UTC OPC surface analysis overlaid.

VIIRS Visible image with the 18 UTC OPC surface analysis overlaid.

I’ll finish this entry with two VIIRS Visible images above showing the majestic beauty of this nor’easter.  The 18 UTC OPC surface analysis depicts the storm at a maximum intensity of 955 mb, after a 45 mb drop in 24 hours!  This qualifies as one of the most explosive cyclones on record.  Another tidbit. . .this was the strongest storm in this part of the Atlantic since Hurricane Sandy (2012).

Thanks for reading!

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VIIRS True Color RGB imagery produced by NASA/SPoRT.  Southwest region domain at 1836UTC, 11 March 2014.

VIIRS True Color RGB imagery produced by NASA/SPoRT. Southwest region domain at 1836UTC, 11 March 2014.

In the southwest CONUS region, severe to extreme drought conditions exist in many areas.  In particular southwest Colorado, northeast New Mexico and the Texas and Oklahoma panhandle areas are very dry according to the U.S. Drought Monitor.  A building high pressure area developed a strong pressure gradient across these areas during the afternoon of 11 March 2014, resulting in 20-30 kt sustained northerly winds with gusts over 40 kt. Combined with the dry conditions, WFOs in the southwest have been anticipating blow dust events to be large and more frequent with strong Spring cyclones. VIIRS True Color RGB imagery (above) shows the blowing dust in Colorado and Texas, but the clouds in Colorado and Kansas have a similar color and the dry ground characteristics in Texas also look similar in color to the dust.  To provide a more efficient analysis of the blowing dust, VIIRS and MODIS can be used to create an RGB imagery product that shows blowing dust in shades of magenta to differentiate it from clouds and ground features.  This is done using the EUMETSAT recipe for the “Dust RGB” per their “Best Practices” after years of experience with the MeteoSat Second Generation SEVIRI instrument.  This geostationary instrument has similar capabilities to that of the future GOES-R ABI instrument.  Hence VIIRS and MODIS provide operational utility now and demonstrate future capabilities that all U.S. forecasters can use to be ready for the next generation of satellite products.  The VIIRS and MODIS passes show three times from this afternoon to aid forecasters with tracking the dust event.

20140311_1836_sport_viirs_swregion_dust_annotated

MODIS Dust RGB Imagery for 1941UTC 11 March 2014

MODIS Dust RGB Imagery for 1941UTC 11 March 2014

VIIRS Dust RGB Imagery for 2019UTC 11 March 2014

VIIRS Dust RGB Imagery for 2019UTC 11 March 2014

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VIIRS_dnbref_rgb_CO_snowvscloud_19Feb2014_0905_annotated

VIIRS DNB Reflectance RGB within AWIPS/D2d for 17 February 2014 at 0905 UTC over the Colorado, Wyoming, Nebraska, Kansas region

The VIIRS Day-Night Band (DNB) RGB imagery from SPoRT uses the DNB channel for both the red and the green components of the RGB, and then the single channel 11 micron band for the blue component.  So warm, reflective clouds have both red and green and result in a shade of yellow while cold, reflective clouds appear in shades of blue to white.  The image above from 17-February-2014 has a mixture of yellow, blue, and white objects, but the question is: Are all of these areas clouds?  Some of the city lights appear to be distinct, sharp yellow points on the ground with little diffusion of light through clouds even though they are surrounded by shades of yellow.  Notice the area at the intersection of the CO, WY, and NE borders as well as some of the inter-mountain regions of western Colorado and how the city lights in these regions are not blocked, nor spread over a large area due to scattering by the clouds.

VIIRS_ntmicro_rgb_CO_snowvscloud_19Feb2014_0905_annotated

VIIRS Nighttime Microphysics RGB within AWIPS/D2d for 17 February 2014 at 0905 UTC over the Colorado, Wyoming, Nebraska, Kansas region

The Nighttime Microphysics RGB imagery from VIIRS is provided above as a comparison to the DNB.  Using this RGB one can identify areas of clouds and their type.  Several of the areas in question turn out to be surface features as opposed to clouds.  This realization that clouds do not exist in some of the yellow shaded areas of the DNB as well as the fact that city lights are not scattered in these regions, leads one to conclude that the DNB is showing snow on the ground.  Several areas are labeled as “Snow Cover”.  However, note that some clouds do exist.  In fact some low clouds in the inter-mountain west of Colorado are evident in yellowish-green tones, and low- and mid-level clouds are highlighted in northwest Kansas and northeastern Colorado.  The Nighttime Microphysics RGB also hints at the potential of fog in southeast Colorado with dull gray to shades of aqua.  Perhaps snow cover has melted to some extent to provide a moist ground with clear skies overnight that resulted in some very thin, to scattered fog or low clouds. Below are images of the same time but over a wider area in order to provide greater perspective.  Note that much of the yellow shaded areas in the DNB RGB are the result of snow cover vs low cloud features.  Hence VIIRS demonstrates valuable insight to both clouds and surface features at night via reflected moonlight.

VIIRS_dnbref_rgb_CO_snowvscloud_19Feb2014_0905_wideview

VIIRS DNB RGB within AWIPS/D2d for 17 February 2014 at 0905 UTC over the western U.S.

VIIRS_ntmicro_rgb_CO_snowvscloud_19Feb2014_0905_wideview

VIIRS Nighttime Microphysics RGB within AWIPS/D2d for 17 February 2014 at 0905 UTC over the western U.S.

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In the early morning hours of Wednesday, January 29th a deck of low stratus clouds developed over the Copper River Basin in Alaska.  The RGB Night-Time Microphysics product derived from SNPP VIIRS instrument at 1321UTC (4:21am local Alaska time) is shown in the following screen capture from the National Weather Service’s AWIPS workstation at WFO Fairbanks, Alaska.   This view is zoomed into the southern portion of mainland Alaska; the Copper River Basin is northeast of Anchorage and includes the community of Gulkana.  The 1253UTC METAR observation from Gulkana indicated an overcast ceiling of 500ft above ground, with seven miles of horizontal visibility.  The RGB NT Micro depicts the stratus deck with a gray-yellow color, and one can see the low clouds confined by the higher terrain and covering the broad Cooper River Basin as well as following the more narrow Copper River itself as it flows southeast of Gulkana and eventually into the Gulf of Alaska.

Copper Basin annotated

A comparison of the RGB NT Micro product with different VIIRS products from the same SNPP pass is presented in the following 4-panel screen capture.  The RGB NT Micro is in the upper-left, the Day-Night Band is in the upper-right, the 11.45 micron IR is in the lower-right, and the traditional channel differencing fog product is in the lower-left.  The deck of stratus clouds over the Copper River Basin is also evident in the longwave IR imagery and the fog product.  The clouds are thin enough that the city lights of are evident through the cloud layer in the Day-Night Band.  In this example, it appears that the stratus deck is most evident in the RGB NT Micro and the fog product, and least evident in the Day-Night Band.

Copper Basin 4-Panel

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