Tag Archives: M-7

Sea-effect Snow

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Take a look at this image:

Photo credit: İskender Şengör via Severe Weather Europe on Facebook

Photo credit: İskender Şengör via Severe Weather Europe on Facebook

Is this picture from A) the Keweenaw Peninsula of Michigan in 1978? B) Orchard Park, New York in November 2014 (aka “Snowvember”)? or C) İnebolu, Turkey from just last week?

If you pay attention to details, you will have noticed that I credited İskender Şengör with the picture and properly surmised that the answer is C. If you don’t pay attention to details, get off my blog! The details are where all the interesting stuff happens! You’d never be able to identify small fires or calculate the speed of an aurora  or explain the unknown without paying attention to details.

If you follow the weather (or social media), you probably know about lake-effect snow. (Who can forget Snowvember?) But, have you heard of sea-effect snow?

Areas downwind of the Great Lakes get a lot more snow than areas upwind of the Lakes. I was going to explain why in great detail, but this guy saved me a lot of time and effort. (I have since been notified that much of the material in that last link was lifted from a VISIT Training Session put together by our very own Dan B. You can watch and listen to that training session here.) The physical processes that cause lake-effect snow are not limited to the Great Lakes, however. Anywhere you have a large body of relatively warm water (meaning it doesn’t freeze over) with episodes of very cold winds in the winter you get lake-effect or sea-effect snow.

When you think of the great snowbelts of the world, you probably don’t think of Turkey – but you should! Arctic air outbreaks associated with strong northerly winds blowing across the Black Sea can generate snow at the same rate as Snowvember or Snowpocalypse or Snowmageddon or any other silly name that the media can come up with that has “snow” in it (Snowbruary, Snowtergate aka Frozen-Watergate, Snowlloween, Martin Luther Snow Day, Snowco de Mayo, Snowth of July… Just remember, I coined all of these phrases if you hear them later). Plus, the Pontic Mountains provide a greater upslope enhancement than the Tug Hill Plateau in Upstate New York.

One such Arctic outbreak occurred from 7-9 January 2015, resulting in the picture above. Parts of Turkey received 2 meters (!) of snow (78 inches to Americans) in a 2-3 day period, as if you couldn’t tell from that picture or this one.

From satellites, sea-effect snow looks just like lake-effect snow. (Duh! It’s the same physical process!) Here’s a VIIRS “True Color” image of the lake-effect snow event that took place last week on the Great Lakes:

VIIRS "True Color" RGB composite, taken 19:24 UTC 7 January 2015

VIIRS “True Color” RGB composite, taken 19:24 UTC 7 January 2015.

Wait – that’s no good! We need to be able to distinguish the snow from the clouds. Let’s try that again with the “Natural Color” RGB composite:

VIIRS "Natural Color" RGB composite, taken 19:24 UTC 7 January 2015

VIIRS “Natural Color” RGB composite, taken 19:24 UTC 7 January 2015.

That’s better. Notice how the clouds are formed right over the lakes and how the clouds organize themselves into bands called “cloud streets“. The same features are visible in the sea-effect snow event over Turkey (from one day later):

VIIRS "Natural Color" RGB composite, taken 10:36 UTC 8 January 2015

VIIRS “Natural Color” RGB composite, taken 10:36 UTC 8 January 2015.

Look at how much of Turkey is covered by snow! (Most of that snow cover is from the low pressure system that passed over Turkey a couple days before the sea-effect snow machine kicked in.) And – *cough* attention to details *cough* – you can even see snow over Greece and more sea-effect snow on Crete. There’s also snow down in Syria, Lebanon and Israel (Israel is off the bottom of the image), which is bad news for Syrian refugees.The heavy snow has shut down thousands of roads, closed schools and businesses, and was even the source of a political scandal.

But, on the plus side, the Arctic outbreak in the Middle East brings a unique opportunity to see palm trees covered in snow. And, how often do you get to see the deserts of Saudi Arabia covered in snow? (EUMETSAT has provided more satellite images of this event at their Image Library.)

Take another look at that image over the Black Sea. See how the biggest snow band extends south (and curving to the southeast) from the southern tip of the Crimean Peninsula? That is an example of how topography impacts these snow events. Due to differences in friction, surface winds are slightly more backed over land than over water, therefore areas of enhanced surface convergence exist downwind of peninsulas. The snow bands are more intense in these regions of enhanced convergence. There are also bigger than normal snow bands downwind of the easternmost and westernmost tips of Crimea, and extending south from every major point along the west coast of the Black Sea. This is not a coincidence. Land-sea (or land-lake) interactions explain this. Go back and listen to the VISIT training session for more information.

Sea-effect snow affects other parts of the globe as well. It’s why the western half of Honshu (the big island of Japan) and Hokkaido are called “Snow Country“. Japan was also hit with a major sea-effect snowstorm last week and, of course, VIIRS caught it:

VIIRS "Natural Color" RGB composite, taken 03:48 UTC 8 January 2015

VIIRS “Natural Color” RGB composite, taken 03:48 UTC 8 January 2015.

See the clear skies over Korea and the cloud streets that formed over the Sea of Japan? Classic sea-effect clouds. You can even see snow all along the west coast of Honshu in between the breaks in the clouds. Topographic impacts are once again visible. Notice the intense snow band extending southeast from the southern tip of Hokkaido/northern tip of Honshu similar to the super-strength snow band off of Crimea. And there’s another one downwind of the straits between Kyushu and Shikoku. Another detail in this image you should have noticed is the impact that Jeju Island has on the winds and clouds. Those are classic von Kármán vortices which we have discussed before.

Fortunately, 8 January 2015 was near a full moon, so the Day/Night Band was able to capture a great image of these von Kármán vortices:

VIIRS Day/Night Band image, taken 18:09 UTC 7 January 2015

VIIRS Day/Night Band image, taken 18:09 UTC 7 January 2015.

So, to the people of the Great Lakes: Remember you’re not alone. There are people in Turkey and Japan who know what you go through every winter.

 

UPDATE #1: While I was aware (and now you are aware) that sea-effect snow can impact Cape Cod, it was brought to my attention that there is a sea-effect snow event going on there today (13 January 2015). Here’s what VIIRS saw:

VIIRS "Natural Color" RGB composite, taken 17:29 UTC 13 January 2015

VIIRS “Natural Color” RGB composite, taken 17:29 UTC 13 January 2015.

According to sources at the National Weather Service, some places have received 2-3 cm (~ 1 inch) of snow in a four-hour period. It’s not the same as shoveling off your roof in snow up to your neck, but it’s something!

Bárðarbunga, the Toxic Tourist Trap

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Quick: what was the name of that Icelandic volcano that caused such a stir a few years ago? Oh, that’s right. You don’t remember. No one remembers. (Unless you live outside the U.S. in a place where you might have actually heard someone say the name correctly.) To Americans, it will forever be known as “That Icelandic Volcano” or “The Volcano That Nobody Can Pronounce” – even though it is possible to pronounce the name. Say it with me: Eye-a-Fiat-la-yo-could (Eyjafjallajökull).

Well, back at the end of August 2014 another volcano erupted in Iceland, and there is no excuse for not being able to pronounce this name correctly: Bárðarbunga. (OK, you have one excuse: use of the letter ð is uncommon outside of Iceland. In linguistics, ð is a “voiced dental fricative” which, in English, is a voiced “th”. “The” has a voiced “th”. “Theme” has an un-voiced “th” or, rather,  “voiceless dental non-sibilant fricative“.) Look, you don’t want to offend any Icelanders, so say it right:

“Bowr-thar-Bunga.” See, it’s easy to say. (You may see people who are afraid of the letter ð refer to the recent eruption as Holuhraun [pronounced “Ho-lu-roin”], because Bárðarbunga is part of the Holuhraun lava field. So be aware of that.)

I know what you’re going to ask: “What is so special about this volcano? I haven’t heard anything about it up to this point, so why should I care?” You haven’t heard anything about it because you don’t live in Iceland or in Europe, which is downwind of Iceland. And, why should you care? Let me count the ways in the rest of this blog post.

You probably have heard of Kīlauea (and have no trouble pronouncing that name) and the lava flow that inched its way towards the town of Pahoa. Kīlauea has been continuously erupting since 1983. Bárðarbunga erupted on 29 August 2014 and has been spewing lava ever since, which at this point, is over 100 days of non-stop erupting. It’s Iceland’s version of Kīlauea. (Hopefully, it won’t continue to erupt for another 30 years.)

Just like Kīlauea, Bárðarbunga is attracting tourists from all over the world. It seems every wannabe photographer and videographer has gone (or wants to go) to Iceland to try to come up with the next viral video showing the breathtaking lava flows. Seriously, do a search for Bardarbunga or Holuhraun on YouTube or vimeo and see how many results show up. Here’s a pretty typical example (filmed by someone from Iceland):

Want to join in the fun? Just grab your camera, head to Iceland, hire an airplane or helicopter pilot, and find the most dramatic music you can think of to go along with your footage. Watch out, though – the airspace around the volcano can be rather crowded. As this video shows, it can be hard to film the volcano without other aircraft getting in the way.

If photography is more your thing, here are the latest images of the eruption on Twitter. (Look for the pictures of Beyonce and Jay-Z. If Twitter is correct, they flew over the volcano for his birthday. Viewing the eruption has gone mainstream! You’re too late, hipsters! Good luck getting to the next volcanic eruption before it becomes cool.)

Back to the matter at hand: why you should care about Bárðarbunga. After its first 100 days of erupting, it has created a field of new lava (76 km2) that is larger than the island of Manhattan (59 km2). The volcano has been creating a toxic plume of SO2 for the last 100 days that is making it difficult to breathe. (Here are some of the known health effects of breathing SO2.) SO2 can ultimately be converted into sulfuric acid (acid rain), depending on the chemistry in the air around the volcano. And while it may not be producing as much ash as Eyjafjallajökull did, VIIRS imagery shows it is producing ash, which is a threat to aircraft.

If you follow this blog, you know the best RGB composite for detecting ash is the True Color composite. This is because the visible wavelength channels that make the composite are sensitive to the scattering of light by small particles, like dust, smoke and ash. Iceland is a pretty cloudy place, so it’s not always easy to spot the ash plume, so here it is at its most visible:

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 12:57 UTC 11 September 2014

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 12:57 UTC 11 September 2014. The red arrow points to the location of Bárðarbunga.

Click on the image (or any other image) to see the full resolution version. The red arrow shows the location of Bárðarbunga. In case you’re wondering, the borders drawn inside the island are IDL’s knowledge of the boundaries of lakes and glaciers (jökull in Icelandic). The big one just south of the red arrow is Vatnajökull – the largest glacier in Europe and one of three national parks in Iceland. (If you want to go there, be aware of closures due to volcanic activity.)

See the ash plume extending from the red arrow to the east-northeast out over the Atlantic Ocean? Now, try to find the ash plume in this animation of True Color images from 29 August to 14 October 2014:

Animation of VIIRS True Color images of Iceland 29 August - 14 October 2014

Animation of VIIRS True Color images of Iceland 29 August – 14 October 2014

As with most of my animations, I have selectively removed images where it was too cloudy to see anything. Sometimes, the steam from the volcano mixes with the ash to make its own clouds, much like a pyrocumulus. Watch for the ash to get blown to the northwest and then southwest in early October. In case you can’t see it, here’s a static example:

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 12:15 UTC 10 October 2014

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 12:15 UTC 10 October 2014. The red arrow shows the location of Reykjavik.

This time, the red arrow shows Reykjavik, the nation’s capitol and likely only city in Iceland you’ve heard of. The ash plume is pretty much right over Reykjavik!

Over the course of the first 100 days, no place in Iceland has been kept safe from the ash plume. But, that’s not the only threat from Bárðarbunga: I also mentioned SO2. If you recall from our look at Copahue (Co-pa-hway – say it right!) the EUMETSAT Dust algorithm is sensitive to SO2. So, can we detect the toxic sulfur dioxide plume from Bárðarbunga? Of course! But, it does depend on cloudiness and just how much (and how high) SO2 is being pumped into the atmosphere.

If you read my post on Copahue, you should have no trouble picking out the sulfur dioxide plume in this image of Bárðarbunga:

EUMETSAT Dust RGB composite applied to VIIRS, 12:57 UTC 11 September 2014

EUMETSAT Dust RGB composite applied to VIIRS, 12:57 UTC 11 September 2014

This image is from the same time as the first True Color image above, when the plume was very easy to see. Also note the large quantity of contrails (aka “chemtrails” to the easily misled). Those are the linear black streaks west of Iceland. If you’re confident in your ability to see the sulfur dioxide, see how often you can pick it out in this animation:

Animation of EUMETSAT Dust RGB images from VIIRS (29 August - 10 October 2014)

Animation of EUMETSAT Dust RGB images from VIIRS (29 August – 10 October 2014)

Some detail is lost because an RGB composite may contain as many as 16 million colors, while the .gif image standard only allows 256. But, you can still see the pastel-colored SO2 plume, which almost looks greenish under certain conditions due to interactions with clouds. Also note the volcano itself appears cyan – the hottest part of the image has a cool color! Unusual in a composite that makes almost everything appear red or pink.

If you want to see the volcano look more like a hot spot, here are animations of the shortwave IR (M-13, 4.0 µm) and the Fire Temperature RGB composite (which I promote whenever I can). I should preface these animations by saying I have not removed excessively cloudy images but, at least 80% of the days have two VIIRS afternoon overpasses and, to reduce filesizes, I have kept only one image per day:

Animation of VIIRS M-13 images of Iceland (29 August - 15 October 2014)

Animation of VIIRS M-13 images of Iceland (29 August – 15 October 2014)

The Fire Temperature RGB is made up of M-10 (1.6 µm; blue), M-11 (2.25 µm; green) and M-12 (3.7 µm; red):

Animation of VIIRS Fire Temperature RGB images of Iceland (29 August - 15 October 2014)

Animation of VIIRS Fire Temperature RGB images of Iceland (29 August – 15 October 2014)

No surprise, molten rock is quite hot! That area of lava has saturated my color table for M-13 and it saturated the Fire Temperature RGB. As I’ve said before, only the hottest fires show up white in the Fire Temperature RGB and lava is among the hottest things you’ll see with VIIRS. Sometimes, you can see the heat from the volcano through clouds (and certainly through the ash plume)! It’s also neat to watch the river of lava extend out to the northeast and then cool.

To quantify it a bit more, the first day VIIRS was able to see the hot spot of Bárðarbunga (31 August 2014), the M-13 brightness temperature was the highest I’ve seen yet: 631.99 K. The other midwave-IR channels (M-12 and I-4; 3.7 and 3.74 µm, respectively) saturate at 368 K. The Little Bear Fire (2012) peaked at 588 K and that fire was hot enough to show up in M-10 (1.6 µm) during the day, so it’s no wonder that we’ve saturated the Fire Temperature RGB.

There’s one more interesting way to look at Bárðarbunga using a new RGB composite. When I was first tipped to this event, I saw this image from NASA, which you can read more about here. That image was taken by the Operational Land Imager (OLI) from Landsat-8 and is a combination of “green, near-infrared and shortwave infrared” channels. Applying this to VIIRS, that combination becomes M-4 (0.55 µm), M-7 (0.87 µm) and M-11 (2.25 µm), which is similar to the Natural Color composite (M-5, 0.64 µm; M-7, 0.87 µm; M-10, 1.61 µm) except for a few notable differences. M-4 is more sensitive to smoke and ash and vegetation than M-5. And M-11 is more sensitive to fires and other hotspots than M-10.

The differences are subtle, but you can see them in this direct comparison:

Comparison between VIIRS "Natural Color" and "False Color with Shortwave IR" RGB composites (12:38 UTC 14 October 2014)

Comparison between VIIRS “Natural Color” and “False Color with Shortwave IR” RGB composites (12:38 UTC 14 October 2014)

NASA calls this RGB composite “False Color with Shortwave Infrared,” although I’m sure there has to be a better name. Any suggestions?

Most of my images and loops have come from the first 45 days after eruption. This was a very active period for the volcano, and is where most of the previously mentioned videos came from. (And trust me, you and your browser couldn’t handle the massive animations that would have resulted from using all 100+ days of images.) To prove Bárðarbunga has gone on beyond that, here’s one of the new RGB composites from 17 November 2014:

VIIRS false color RGB composite of channels M-4, M-7 and M-11, taken 13:42 UTC 17 November 2014

VIIRS false color RGB composite of channels M-4, M-7 and M-11, taken 13:42 UTC 17 November 2014

This image really makes Iceland look like a land of fire and ice, which is exactly what it is!

Hell Froze Over (and the Great Lakes, too)

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This has been some kind of winter. The media has focused a lot of attention on the super-scary “Polar Vortex” even though it isn’t that scary or that rare. (I wonder if Hollywood will make it the subject of the next big horror movie in time for Halloween.) Many parts of Alaska have been warmer than Georgia, with Lake Clark National Park tying the all-time Alaskan record high temperature for January (62 °F) on 27 January 2014. (Atlanta’s high on that date was only 58 °F.) Sacramento, California broke their all-time January record high temperature, reaching 79 °F three days earlier. In fact, many parts of California had record warmth in January, while everyone on the East Coast was much colder than average. Reading this article made me think of an old joke about statisticians: a statistician is someone who would say: if your feet are stuck in a freezer and your head is stuck in the oven, you are, on average, quite comfortable.

One consequence of the cold air in the eastern United States is that Hell froze over. No, not the Gates of Hell in Turkmenistan. This time I’m talking about Hell, Michigan. Hell is a nice, little town whose residents never get tired of people telling that joke.

It has been so cold in the region around Hell that the Great Lakes are approaching a record for highest percentage of surface area covered by ice. This article mentions some of the benefits of having ice-covered Lakes, including: less lake-effect snow, more sunshine and less evaporation from the Lakes, which would keep lake levels from dropping. Although, that is at the cost of getting ships stuck in the ice, and reducing the temperature-moderating effects of the Lakes, which allows for colder temperatures on their leeward side.

This article (and many other articles I found) uses MODIS “True Color” images to highlight the extent of the ice. Why don’t they show any VIIRS images? Well, I’m here to rectify that.

First off, I can copy all those MODIS images and show the “True Color” RGB composite from VIIRS:

VIIRS "True Color" RGB composite of channels M-3, M-4 and M-5, taken 17:27 UTC 11 February 2014

VIIRS "True Color" RGB composite of channels M-3, M-4 and M-5, taken 17:27 UTC 11 February 2014

While it was a rare, sunny winter day for most of the Great Lakes region on 11 February 2014, it’s hard to tell that from the True Color imagery. I mean, look at this True Color MODIS image shown on NPR’s website. Can you tell what is ice and what is clouds?

There are ways of distinguishing ice from clouds, which I have talked about before but, it doesn’t hurt to look at these methods again and see how well they do here. First, let’s look at my modification of the EUMETSAT “Snow” RGB composite:

VIIRS "Snow" RGB composite of channels M-11, M-10 and M-7, taken 17:27 UTC 11 February 2014

VIIRS "Snow" RGB composite of channels M-11, M-10 and M-7, taken 17:27 UTC 11 February 2014

This “Snow” RGB composite differs by using reflectances at 2.25 µm in the place of the 3.9 µm channel that EUMETSAT uses. (Their satellite doesn’t have a 2.25 µm channel.) It’s easy to see where the clouds are now. Of course, now the snow and ice appear hot pink, which you may not find aesthetically pleasing. And it certainly isn’t reminiscent of snow and ice.

If you don’t like the “Snow” RGB, you may like the “Natural Color” RGB composite:

VIIRS "Natural Color" RGB composite of channels I-01, I-02 and I-03, taken 17:27 UTC 11 February 2014

VIIRS "Natural Color" RGB composite of channels I-01, I-02 and I-03, taken 17:27 UTC 11 February 2014

This has the benefit of making snow appear a cool cyan color, and has the added benefit that you can use the high-resolution imagery bands (I-01, I-02 and I-03) to create it. There is twice the resolution in this image than in the Snow and True Color RGB images. Here’s another benefit you may not have noticed right away: the clouds, while still white, appear to be slightly more transparent in the Natural Color RGB. This makes it a bit easier to see the edge of the ice on the east side of Lake Michigan and the center of Lake Huron, for example.

If you’re curious as to how much ice is covering the lakes, here are the numbers put out by the Great Lakes Environmental Research Laboratory (which is about a 25 minute drive from Hell) from an article dated 13 February 2014:

Lake Erie: 96%; Lake Huron: 95%; Lake Michigan: 80%; Lake Ontario: 32% and Lake Superior: 95%. This gives an overall average of 88%, up from 80% the week before. The record is 95% set in 1979, although it should be said satellite measurements of ice on the Great Lakes only date back to 1973.

Why does Lake Ontario have such a low percentage? That last article states, “Lake Ontario has a smaller surface area compared to its depth, so it loses heat more slowly. It’s like putting coffee in a tall, narrow mug instead of a short, wide one. The taller cup keeps the coffee warmer.”  Doesn’t heat escape from the sides of a mug as well as the top? And isn’t Lake Superior deeper than Lake Ontario? Another theory is that “Lake Ontario’s depth and the churning caused by Niagara Falls means that it needs long stretches of exceptionally cold weather to freeze.”  Does Niagara Falls really have that much of an impact on the whole lake?

So, what is the correct explanation? I’m sorry, VIIRS can’t answer that. It can only answer “How Much?” It can’t answer “Why?”

 

BONUS UPDATE (17 February 2014):

It has come to my attention that the very next orbit provided better images of the Great Lakes, since they were no longer right at the edge of the swath. Here, then, are the True Color, Snow and Natural Color RGB composite images from 19:07 UTC, 11 February 2014:

VIIRS "True Color" composite of channels M-3, M-4 and M-5, taken 19:07 UTC 11 February 2014

VIIRS "True Color" composite of channels M-3, M-4 and M-5, taken 19:07 UTC 11 February 2014

 

VIIRS "Snow" RGB composite of channels M-11, M-10 and M-7, taken 19:07 UTC 11 February 2014

VIIRS "Snow" RGB composite of channels M-11, M-10 and M-7, taken 19:07 UTC 11 February 2014

 

VIIRS "Natural Color" composite of channels I-01, I-02, and I-03, taken 19:07 UTC 11 February 2014

VIIRS "Natural Color" composite of channels I-01, I-02, and I-03, taken 19:07 UTC 11 February 2014

 

UPDATE #2 (18 March 2014): The Great Lakes ice cover peaked at 92.2% on 6 March 2014, just short of the all-time record in the satellite era. March 6th also happened to be a clear day over the Great Lakes, and VIIRS captured these images:

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 18:35 UTC 6 March 2014

VIIRS True Color RGB composite of channels M-3, M-4 and M-5, taken 18:35 UTC 6 March 2014

 

VIIRS Natural Color RGB composite of channels M-5, M-7 and M-10, taken 18:35 UTC 6 March 2014

VIIRS Natural Color RGB composite of channels M-5, M-7 and M-10, taken 18:35 UTC 6 March 2014

Wild Week of Wildfires, Part III

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The last two posts covered flooding. Now, a month later, we are back to covering last year’s most common topic: wildfires. This time, we’ll make a game out of it. Keep in mind that, for many operational fire weather forecasters, this isn’t a game – it is information that could prove useful in saving lives or homes from destruction. If you have read the earlier posts on fire detection and haven’t forgotten what you’ve been told (here’s a good one to go back and read), this should be easy for you.

The following images are the unmapped data from three consecutive VIIRS granules over the Southwest U.S., starting at 20:36 UTC 11 June 2013. The “raw” data has been processed to produce the “True Color”, “Natural Fire Color” and “Fire Temperature” RGB composites. Plus, the brightness temperature data from channel M-13 (4.0 µm) has a color table applied to it to aid in fire detection. Satellite channels near 4 µm are the “industry standard”, so to speak, for detecting fires as they are highly sensitive to sub-pixel heat sources like fires. The “Natural Fire Color” and “Fire Temperature” composites are RGB composites developed just for VIIRS that both had their debut on this very blog.

The question is: how many fires can you see? Remember, you have to allocate resources (firefighters, helicopters, planes, etc.) based on your assessment. The media is hounding you for all the latest statistics on each blaze and they can’t wait until the 5:00 briefing. They need the scoop now to get higher ratings. Plus, the crew is loading fire retardant on the plane as you read this. Where should the pilot fly to? Everyone is counting on you! (Of course, you would never have just satellite data by itself in a real-life scenario – but, do you want to play this game, or just think of flaws?)

I’ll give you a hint: You won’t see any fires unless you view each image at full resolution. Click on the image, then on the “3200×2304” link below the banner to see the full resolution version. (You could even open each full resolution image in a new tab, and click between the tabs for easy comparison, assuming you’re not using some archaic version of Internet Explorer or another old browser that doesn’t allow tabs. When you would click on the “3200×2304” link, instead right-click and select “Open in New Tab”. Another option would be to save the images and open them in an image viewing software program that will allow you to zoom in more than 100% but, that is starting to sound like a lot of work and I’m not sure I want to play this game anymore. It’s too complicated. By the way, if that’s the way you feel, don’t become the manager of a fire incident team.)

I’ll give you another hint: Many of the hot spots that indicate fires are only 1-2 pixels in size. Be prepared to look for needles in the haystack, and make sure you have your reading glasses on, if you need them.

VIIRS "True Color" composite of channels M-03, M-04 and M-05, taken at 20:36 UTC 11 June 2013

VIIRS "True Color" composite of channels M-03, M-04 and M-05, taken at 20:36 UTC 11 June 2013

VIIRS "Natural Fire Color" composite of channels M-05, M-07 and M-11, taken 20:36 UTC 11 June 2013

VIIRS "Natural Fire Color" composite of channels M-05, M-07 and M-11, taken 20:36 UTC 11 June 2013

VIIRS "Fire Temperature" composite of channels M-10, M-11 and M-12, taken 20:36 UTC 11 June 2013

VIIRS "Fire Temperature" composite of channels M-10, M-11 and M-12, taken 20:36 UTC 11 June 2013

VIIRS channel M-13 image, taken 20:36 UTC 11 June 2013

VIIRS channel M-13 image, taken 20:36 UTC 11 June 2013

So, did you see them all? You should have identified 12 fires. Did you find less than 12? Some of them are hard (or impossible) to see in some of the images. Did you find more than 12? The color scale used on the M-13 image led to false alarms, so you can be forgiven if that’s what caused you count too many.

This example shows some of the complicating factors when trying to identify fires from satellites. It also shows why fire managers never rely on satellite data alone. Now, having said that, VIIRS can and does provide useful information on fires.

First, here’s the answer (link goes to PDF) from the National Interagency Fire Center. They identified 15 active “large incident” fires on 12 June 2013. (They update their maps once per day, so all the fires that started on 11 June make it on the 12 June map.) But, there are differences between their map and what VIIRS saw.

First, the Mail Trail fire (#5 in the PDF) is outside the domain of these three VIIRS granules, so you couldn’t have found that in these images. Fires #3, 4 and 7 (Healy, Porcupine and Ferguson) are obscured by clouds, and/or were mostly contained, transitioning from active to inactive. The Tres Lagunas Fire (#13) started back in May and is undergoing mop up activities. The hot spots from that fire (if there are any left) aren’t visible in the images, but the burn scar is. That leaves the Stockade (#1), Crowley Creek (#2), Hathaway (#6), Fourmile (#8), Silver (#9), Thompson Ridge (#10), Jaroso (#11), Big Meadows (#12), Royal Gorge (#14), and Black Forest (#15) – 10 fires which are all visible in the VIIRS images. Plus, VIIRS saw two more fires that are not included on that list: one in southern California (near the Salton Sea) that I couldn’t find any information on, plus a pellet plant fire in Show Low, Arizona. (Small fires in towns are usually outside the scope of the National Interagency Fire Center, so they don’t bother to list those.)

I would argue that the “Fire Temperature” composite worked the best at identifying each of these fires, but all 4 images have their uses. Here’s the Fire Temperature RGB image with the visible fires identified:

VIIRS "Fire Temperature" composite of channels M-10, M-11 and M-12, taken 20:36 UTC 11 June 2013

VIIRS "Fire Temperature" composite of channels M-10, M-11 and M-12, taken 20:36 UTC 11 June 2013

Answer honestly. Which fires did you see, and which fires did you miss?

The Fire Temperature RGB takes advantage of the VIIRS channels in the portion of the electromagnetic spectrum ranging from the near-infrared (NIR) to the shortwave infrared (SWIR). The blue component is M-10 (1.61 µm), the green component is M-11 (2.25 µm) and the red component is M-12 (3.7 µm). As wavelength increases over this range, the contribution of the Earth’s emission sources increases and the contribution from the sun decreases. As a result, only the hottest hot spots show up in M-10, as they have to be seen over the large signal of radiation from the sun reflecting off the Earth’s surface. In M-12 (as in M-13), hot spots from fires produce more radiation at that wavelength than the amount of reflected solar radiation. M-11 is somewhere in the middle. That means relatively cool (e.g. smoldering) or small fires only show up in M-12, which makes those pixels appear red. Pixels containing fires hot enough or large enough to show up in M-11 will take on an orange to yellow color. Pixels containing fires hot enough or large enough to show up in all three channels will appear white.

You have to be careful, though, as some pixels in the Fire Temperature RGB appear red, even though there aren’t any fires in them. A few of these pixels show up red in the M-13 image, and are labelled as “not a fire/false alarm”:

VIIRS M-13 image, taken 20:36 UTC 11 June 2013

VIIRS M-13 image, taken 20:36 UTC 11 June 2013

According to the color table used, any pixel with a brightness temperature above 340 K (67 °C) will be colored, with colors ranging from red to orange to pale yellow as temperature increases. Now, look at that area in the True Color image (or on Google Maps):

VIIRS "True Color" composite of channels M-03, M-04 and M-05, taken 20:36 UTC 11 June 2013

VIIRS "True Color" composite of channels M-03, M-04 and M-05, taken 20:36 UTC 11 June 2013

That area is very dark – almost black – volcanic rock with very little vegetation that has been baking in the sun all day. It has managed to acquire a brightness temperature that is higher than some of the active fire pixels. The Crowley Creek fire doesn’t show up as red in the M-13 image (the Stockade fire is the one with the yellow and orange pixels) and the Fourmile fire is barely visible. (It has two pixels warmer than 340 K, even though 10 pixels appear red in the Fire Temperature RGB). The color scale in the M-13 image could be applied to a different temperature range, but you’ll always have that trade-off: have the colors start at too high a temperature, and you’ll miss some fires; have the colors start at too low a temperature, and you’ll increase the false alarms.

The True Color image should have helped you identify 5 of the fires. The smoke plumes that show up are a dead giveaway. I’m talking about the Big Meadows, Royal Gorge, Jaroso, Thompson Ridge and Silver fires, of course. There may be smoke with the Hathaway fire, but it would be mixed in with the cirrus clouds and hard to see. Not all fires produce a lot of smoke, though. Having information on the ones that do aids in issuing air quality alerts, among other benefits.

Lastly, the Natural Fire Color image highlights most (but not all) of the fires. Look for the red pixels:

VIIRS "Natural Fire Color" composite of channels M-05, M-07 and M-11, taken 20:36 UTC 11 June 2013

VIIRS "Natural Fire Color" composite of channels M-05, M-07 and M-11, taken 20:36 UTC 11 June 2013

The Natural Fire Color doesn’t show active hot spots at Crowley Creek, and the Hathaway and Fourmile fires are difficult to see, because they aren’t quite hot enough. (Generally speaking, any fire that shows up red in the Fire Temperature RGB is too cold to show up as red in the Natural Fire Color.) But, this composite has the advantage of showing burn scars in addition to the active fires. Burn scars appear dark brown. The Fourmile and Crowley Creek burn scars are visible. Plus, burn scars from last year’s fires still show up: The Whitewater-Baldy, High Park and Waldo Canyon scars are identified. The Tres Lagunas was mentioned above, and it’s burn scar is visible. If you look closely, I’m sure you could find more burn scars from last year’s long fire season.

Here are all four images, zoomed in on each fire at 800%, combined into an animation to highlight how each fire appears in each image:

Animation of M-13, True Color, Natural Fire Color and Fire Temperature imagery zoomed in each fire (20:36 UTC 11 June 2013)

Animation of M-13, True Color, Natural Fire Color and Fire Temperature imagery zoomed in each fire (20:36 UTC 11 June 2013)

For some reason, you have to click to the full resolution version of the image before the animation will display.

Hopefully, this exercise is useful in demonstrating the complications that arise when trying to detect fires from satellites in space, as well as the strengths and weaknesses of some of the various methods VIIRS has at it’s disposal to aid the fire weather community.

Drought in the Land of the Long, White Cloud

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Science fiction fanatics know it as “Middle-earth“.  Abel Tasman, the Dutch explorer who became the first European to sail there, called it “Staten Landt“, which was later changed to Nieuw Zeeland, Nova Zeelandia, and, finally, New Zealand. The native Maori people call it “Aotearoa“, which loosely translates to “the land of the long, white cloud”.

A group of volcanic islands southeast of Australia, New Zealand is known for the Southern Alps, the locations where they filmed the Lord of the Rings trilogy and rugby, although I’m sure there’s more to the country than that. Residents of New Zealand refer to themselves as “kiwis”, although it is not clear if they prefer to be thought of as birds or fruit.

Being an island nation in the mid-latitudes with 17 peaks above 10,000 ft (3,000 m), you might expect there would be no shortage of moisture and uplift to form clouds and precipitation. There are sea breezes, mountain/valley circulations, orographic uplift of prevailing winds, periodic mid-latitude cyclones and the occasional tropical storm to get things started. But, that’s not the case this year.

The North Island is currently experiencing its worst drought in over 30 years. Many places have experienced less than half of normal precipitation this summer, according to NIWA (their version of NOAA). These are places that normally receive 40-80 inches of precipitation per year. (Remember, summer just ended down there and that 500 mm is roughly 20 inches.)

Wellington, the nation’s capital, has begun rationing water for the first time in recorded history (which covers about 170 years). The chair of the Wellington region’s committee in charge of the water supply was quoted as saying, “People should shower with a friend, if that’s an option . . . or put a brick in the toilet. If you know anyone who’s particularly adept at rain dances, then encourage them to get out there and do what they do.”

One of the previous links mentioned that the drought is so bad, it can be seen from space. They didn’t provide evidence to back up that claim, so I guess I have to do it. Here’s what VIIRS saw on 28 January 2013 (before the North Island went 4-6 weeks without any significant precipitation):

"True Color" RGB composite of VIIRS channels M-03, M-04 and M-05, taken 01:49 UTC 28 January 2013

"True Color" RGB composite of VIIRS channels M-03, M-04 and M-05, taken 01:49 UTC 28 January 2013

And here is what VIIRS saw on 21 March 2013 (after 4-6 weeks without significant precipitation):

"True Color" RGB composite of VIIRS channels M-03, M-04, and M-05, taken 02:15 UTC 21 March 2012

"True Color" RGB composite of VIIRS channels M-03, M-04, and M-05, taken 02:15 UTC 21 March 2012

The two images above are “true color” composites. If you look closely at the two images, you might notice significantly less green vegetation in the 21 March 2013 image, particularly in box that covers 39° to 40° S latitude and 174° to 176° E longitude. (Remember, you can see the full-resolution image by clicking on it, and then on the “1434×2120” link below the banner.)

Not convincing? Maybe it shows up a bit better in the “natural color” composite, which has a strong vegetation signal. Here are those images:

False color composite of VIIRS channels M-05, M-07 and M-10, taken 01:49 UTC 28 January 2013

False color composite of VIIRS channels M-05, M-07 and M-10, taken 01:49 UTC 28 January 2013

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False color composite of VIIRS channels M-05, M-07 and M-10, taken 02:15 UTC 21 March 2012

False color composite of VIIRS channels M-05, M-07 and M-10, taken 02:15 UTC 21 March 2012

And just to be clear, here are the images zoomed in on the west side of the North Island, where the drought has hit the hardest:

Drought impact on vegetation in the North Island of New Zealand between 28 January and 21 March 2013

Drought impact on vegetation in the North Island of New Zealand between 28 January (left) and 21 March 2013 (right)

In the image on the left, from 28 January, light green areas represent grassland/pasture (backed up by this land use map) and dark green areas represent forests. In the image on the right, from 21 March, the grassy areas have turned brown while the forests have remained green. Six weeks with almost no rain will do that to grass.

While the “true color” and “natural color” RGB composites are only qualitative (and require viewers to be able to distinguish sometimes subtle changes in the amount of green in the images), there are ways to quantify the “greenness” of vegetation from satellite. The most widely used method is the Normalized Difference Vegetation Index (NDVI for short). The NDVI has been calculated for more than 40 years with Landsat and AVHRR. We can do the same calculation with VIIRS. That’s what is shown below.

VIIRS NDVI images of New Zealand from 28 January and 21 March 2013

VIIRS NDVI images of New Zealand from 28 January (left) and 21 March 2013 (right)

On this color scale, red and yellow colors indicate high values of NDVI (or very green vegetation). Green and blue colors indicate low values of NDVI (sparse, dead or brown vegetation). Notice how most of the North Island has gone from yellow or red in January (on the left) to blue or green in March (on the right). NDVI values have decreased by 20-30% over this period.

I guess if there is one benefit of the drought, it’s that it has been clear enough over New Zealand for satellites to see it. In fact, January and February have broken records for the amount of sunshine in many parts of the country. The land of the long, white cloud hasn’t been living up to its name.