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Archive for the ‘VIIRS’ Category

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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During a brief period in mid-Janaury, when the “Polar Vortex” was safely docked in its home port of Alaska, temperatures over Alaska’s Interior plunged into the 40s and 50s below zero.  Under clear skies and light winds, surface-based radiation inversions decouple a thin bottom layer of air from the free troposphere and produce extreme stratification of temperatures in the vertical over Interior Alaska’s complex terrain.  Long-wave Infrared imagery from polar-orbiting satellites allows forecasters to “see” the topography during these events, since the coldest air settles into the valley bottoms and ground temperatures monotonically moderate with increasing height.

The 2013-2014 winter is the inaugural season for SPoRT’s RGB Night-time Microphysics product.  Given that longwave IR contributes the “B” channel of the RGB NT Micro, one might wonder if topographic features might also be evident in the RGB NT Micro during a cold clear Alaska night.

This figure is a four-panel screen capture from an AWIPS workstation at National Weather Service WFO Fairbanks, Alaska.  All four panels show imagery from the 1321Z (5:21am Alaska Standard Time) pass of the SNPP VIIRS instrument on Monday, January 13th, 2014.  The area shown is zoomed into the “Upper Yukon Valley” of Alaska’s Interior.  The village of Fort Yukon, on the Yukon River, is marked with the star in each panel.  Conditions at this time in the Upper Yukon Valley were clear, calm, and cold, with surface temperatures around Fort Yukon in the 40s below zero.

Upper Yukon 4 Panel annotated

The upper-left panel is the RGB NT Micro using the default color enhancement, the upper-right panel is the Day-Night Band, the lower-right panel is the 11 micron longwave IR, and the lower-left panel is the traditional channel differencing “fog product.”  Topographic features are clearly evident in the DNB image in the upper-right, as well as in the longwave IR image in the lower-right.  But interestingly, the topography is almost entirely non-evident in the RGB NT Micro in the upper-left, despite longwave IR being one of the three components of the RGB image.

Learning to use a new product includes discovering what that product is capable of depicting and *not* depicting under a variety of weather conditions.  The Alaskan winter is an extreme and unusual environment, and this one example indicates that one should not expect to see terrain features in the RGB NT Micro under conditions of clear skies and extreme temperature stratification.  Correspondingly, a “smooth” look to RGB NT Micro imagery in this case does *not* indicate a broad cloud deck covering the terrain.

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SPoRT is conducting an assessment of RGB imagery for Aviation and Cloud Analysis with Alaska WFO partners.  A 17 minute training module for high-latitude application of nighttime RGBs with an Alaska example was created by SPoRT to support this assessment (see SPoRT training page to download or launch module). The Juneau WFO provided feedback for 1/24/14.  Here is a part of their feedback regarding the value of the Nighttime Microphysics RGB imagery from MODIS and VIIRS and an example image from AWIPS/D2d.

WFO Juneau feedback:
“… the microphysics image was very helpful in picking out where the fog and low clouds were in the complex terrain that is the SE panhandle. most of the fog this morning was confined to the narrower valleys and channels while the wider channels were mostly clear. This is possibly due to higher winds still present in the wider channels limiting fog formation there. It also showed little or no fog and low clouds out in the gulf. The microphysics image was very helpful with figuring out fog for zone and marine forecasts. It also helped out with the TAFs with seeing if there were any higher clouds layers above the fog layer.”

AJK_Ntmicro_assess_feedback_for_blog_20140124_0736_annotated

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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).

12Jan2014_VIIRS_DNBReflectance_GulfReflectance

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

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A well defined TROWAL feature that set up over the high plains from eastern NM into western TX and KS on December 21, 2013 was captured very well by the NESDIS snowfall rate product.   A composite radar reflectivity loop in the first image below summarizes the overall evolution of this feature between 12 UTC on December 21st and 00 UTC on the 22nd (click image to loop and enlarge).  Initially temperatures were too warm for snow across much of the area however as a potent cold front shifted south over the region rain changed over to snow.  In the area of greatest instability the snow became heavy at times from near Tucumcari, NM (KTCC) to Dalhart, TX (KDHT).

Composite Radar Reflectivity Loop December 21, 2013.  Click to enlarge.

Composite Radar Reflectivity Loop December 21, 2013. Click to loop and enlarge.

The following series of images compare hourly precipitation reports at several sites across western TX and KS with the NESDIS snowfall rate product.  The first image was captured at 2040UTC and the AWIPS cursor readout at KDUX (Dumas, TX) is shown.  Note the observation is reporting an hourly precipitation accumulation of 0.05 (P0005) with moderate snowfall and a visibility of 1/2SM.  The cursor readout comparison with the QPE product is 0.0544 in/hr.  The following sample point valid for KPYX (Perryton, TX)  is reporting a visibility of 1/4SM however no weather or precipitation is available since it is only an AWOS.  However, the QPE product is sampling a precipitation rate of 0.1064 in/hr which converting with a simple 10:1 snow ratio would equate to heavy snow at 1″ per hour.  The next image was captured at 2236UTC and the cursor readout at KDDC (Dodge City, KS) is shown.  Note the observation is reporting an hourly precipitation accumulation of 0.07 (P0007) with moderate snowfall and a visibility of 1/2SM.  The QPE comparison in the readout shows a rate of 0.092 in/hr.  These values are exceptionally representative of the current conditions and the latency is less than 30 minutes.

NESDIS QPE valid 2040 UTC December 21, 2013.  Note the sample point comparison for the observation at KDUX (Dumas, TX).

NESDIS QPE valid 2040 UTC December 21, 2013. Note the sample point comparison for the observation at KDUX (Dumas, TX).

NESDIS QPE valid 2040 UTC December 21, 2013. Note the sample point comparison for the observation at KPYX (Perryton, TX).

NESDIS QPE valid 2040 UTC December 21, 2013. Note the sample point comparison for the observation at KPYX (Perryton, TX).

NESDIS QPE valid 2236 UTC December 21, 2013. Note the sample point comparison for the observation at KDDC (Dodge City, KS).

NESDIS QPE valid 2236 UTC December 21, 2013. Note the sample point comparison for the observation at KDDC (Dodge City, KS).

After the storm system pulled out of the region the Snow-Cloud RGB product provided a stellar view of this mesoscale band of snowfall.  Modifying temperatures over the following days significantly eroded snowpack in most areas except where the heaviest snow fell.  Local storm reports obtained from the Iowa State website indicated between 6 and 11 inches of snow impacted the area within the central axis of the TROWAL feature.

Snow-Cloud RGB valid at 1704 UTC December 22, 2013.

Snow-Cloud RGB valid at 1704 UTC December 22, 2013.

Snow-Cloud RGB valid at 2014 UTC December 24, 2013.

Snow-Cloud RGB valid at 2014 UTC December 24, 2013.

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I’ve posted about this a few times, but this morning offered another good example of the ability of the Suomi NPP VIIRS Day-Night Band RGB imagery to show low clouds beneath thin cirrus.  First, take a look at the 11-3.9 µm imagery (with the standard color curve) from the VIIRS instrument, valid this morning at approx 0749 UTC.  Focus your attention mainly over southern Texas.

Suomi NPP VIIRS 11-3.9 µm image valid 19 Dec 2013 0749 UTC

Image 1.  Suomi NPP VIIRS 11-3.9 µm image valid 19 Dec 2013 0749 UTC

In the image above, high, cirrus clouds will appear as blue colors, while lower clouds appear yellow.  Notice the bank of low clouds in the northern Gulf extending into portions of extreme SE Texas and southern Louisiana.  Notice that some low clouds can also be observed in and around the thin cirrus to the southwest in southern Texas.  These cloud features show up arguably better in the VIIRS Day-Night Band image from the same time (image 2).

Image 2.  Soumi NPP VIIRS Nighttime Microphysics RGB 19 Dec 0749 UTC

Image 2. Soumi NPP VIIRS Nighttime Microphysics RGB 19 Dec 0749 UTC

With the Nighttime Microphysics RGB, the low clouds appear as an off-white, while the high thin cirrus are the deep reds and blues spreading across much of the CONUS in the image.  Notice the low clouds in southern Texas still cannot be observed very well beneath the cirrus canopy, as the cirrus are mostly opaque to the longer IR wavelengths.  Now, let’s take a look at the VIIRS Day-Night Band imagery.  I like the Day-Night Band Radiance RGB best for this particular situation (image 3).

Image 3.  Suomi NPP VIIRS Day-Night Band Radiance RGB 19 Dec 2013 0749 UTC

Image 3. Suomi NPP VIIRS Day-Night Band Radiance RGB 19 Dec 2013 0749 UTC

Since the cirrus are mostly translucent in the visible portion of the spectrum, the low clouds can be seen beneath.  Also, given that the Day-Night Band Radiance RGB has an IR component, this results in better delineation between high and low clouds.  In this situation, forecasters would have a much better idea of the extent of the low cloud deck.  Observations from 0800Z indicated the cloud bases were around 1-2 kft in that area of southern Texas, which could have significant impacts on sensible weather and forecasts, especially for aviation.

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