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Old 04-10-2014, 02:07   #46
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Re: Northwest Passage - 2014

I think the issue of global warming/global cooling is relevant to the NWP discussion. However, there is still disagreement amongst many of the world's elite scientists about the trend, the cause, etc. So, I don't think we will solve that debate here.

Therefore, the feasibility of passing the NWP each season, and therefore planning to do so, shall remain unpredictable in the short term. For the time being it looks arriving at the entrance of the NWP and waiting for a window to appear, with the risk of one not appearing at all,seems as much as yachts can do.
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Old 04-10-2014, 08:39   #47
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Re: Northwest Passage - 2014

The only disagreement is from the hacks hired by oil companies to spread disinformation to the masses. Virtually all scientific consensus is that the global warming is caused by man's activities.
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Old 04-10-2014, 10:13   #48
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Re: Northwest Passage - 2014

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Originally Posted by StuM View Post
How long a term? Temperatures have been decreasing for the last 8,000 years or so as we slide towards the next glacial and we are still lower than any of the last "climate optimums" in that period.

If you mean the linear trend since we came out of the little ice age in the 1850s, then using what data set?


RSS - which shows zero warming for over 18 years?
Wood for Trees: Interactive Graphs
HADCRUT4? Looks like the cyclic pattern is repeating and we will be going into another "ice age" scare like the early 70s.

Wood for Trees: Interactive Graphs
Roy Spencer and John Christy at the University of Alabama Hunstville have concluded that RSS data shows spurious cooling. As signatories to the Cornwall Alliance Evangelical Declaration on Global Warming they are AGW deniers. The declaration uses the term "deny."

Their own satellite data shows 2 decades of warming.




Cowtan and Way have demonstrated that HADCRUT4 underestimates Arctic temperatures. This has been confirmed by Natural Resources Canada which shows more warming in the Arctic than further south.

BTW - there was little scientific basis for an "ice age" scare in the 1970's. Science journal articles on warming outnumbered cooling by a ratio of 6:1. The mainstream media got it wrong.
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Old 04-10-2014, 14:22   #49
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Re: Northwest Passage - 2014

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Originally Posted by StuM View Post
How long a term? Temperatures have been decreasing for the last 8,000 years or so as we slide towards the next glacial and we are still lower than any of the last "climate optimums" in that period.

If you mean the linear trend since we came out of the little ice age in the 1850s, then using what data set?


RSS - which shows zero warming for over 18 years?
Wood for Trees: Interactive Graphs
HADCRUT4? Looks like the cyclic pattern is repeating and we will be going into another "ice age" scare like the early 70s.

Wood for Trees: Interactive Graphs
The rate of temperature increase looks unprecedented to me.


What’s the hottest Earth has been “lately”? | NOAA

Quote:
...The 11,000-year temperature reconstruction shows global average temperature increasing after the end of the last ice age and leveling off about 7550 and 3550 BC. After that time, global temperatures dropped until the "Little Ice Age," bottoming out somewhere between AD 1450 and 1850. Afterwards temperatures rose again, first slowly then very rapidly...

For most of the past 10,000 years, global average temperature has remained relatively stable and low compared to earlier hothouse conditions in our planet's history. Now, temperature is among the highest experienced not only in the “recent” past—the past 11,000 years or so, during which modern human civilization developed—but also probably for a much longer period.

Carrie Morrill of the National Climatic Data Center explains, "You'd have to go back to the last interglacial [warm period between ice ages] about 125,000 years ago to find temperatures significantly higher than temperatures of today."
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Old 06-11-2014, 22:04   #50
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Re: Northwest Passage - 2014

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Originally Posted by JRM View Post
I found this idea fascinating. Google wasn't much of a friend, and I didn't find any decent data in the few minutes I spent searching, so I decided to generate my own with a completely unscientific but very entertaining experiment.

I have access to a recording thermal camera, so I figured I'd give it a shot and see what happens. Lacking access to any real ice bergs, I used a bucket filled with water and ice from our ice machine.

The pics are:

A bucket of ice
Ice dumped at the base of a tree
A bucket of ice with no water
A bucket of ice filled with water
Ice water with my thumb for contrast
Ice water stirred up for a while

As I discovered, this camera is able to differentiate ice from cold water, even when the water is really cold. Now, I'm not willing to go so far as to extrapolate these results into berg spotting abilities, but I did have a good time doing it.

JRM
Unfortunately, I doubt that thermals would be of much help in spotting icebergs. Icebergs will be close to 32 degrees farenheit. Seawater will also be close to 32 degrees farenheit. Because of the very low contrast in temperatures, the icebergs will not be very visible.

Your experiment shows that 0 degree ice, 40 degree water, and 60 degree dirt all show as different colors on a thermal viewer. I do not think you can extrapolate the results to the sea conditions near Greenland. (But it still looked like it was fun)
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Old 07-11-2014, 05:34   #51
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Re: Northwest Passage - 2014

Look at this picture.

Water was 32. The air was reading 40 but there was a blowing mist, sorta like frozen mist. While it doesn't look it they were good 6 foot seas, maybe 8. Freakin cold. 25 knots. The bergs were disintegrating because they were grounded and the bits were floating off. I doubt the thermal camera could read through the mist to pick up low lying bits.

Maybe with less wind and clear air.
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Old 07-11-2014, 09:55   #52
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Re: Northwest Passage - 2014

I don't know. Water and ice have very different emissivity. If you have two items of the same temperature but different emissivity, the brightness will be different.

A black and white thermal camera of this type isn't looking at the spectrum of the emission, just the brightness.

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Old 07-11-2014, 11:16   #53
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Re: Northwest Passage - 2014

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Originally Posted by cwyckham View Post
I don't know. Water and ice have very different emissivity. If you have two items of the same temperature but different emissivity, the brightness will be different.

A black and white thermal camera of this type isn't looking at the spectrum of the emission, just the brightness.

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The two items with differing emissivities will show up at different apparent temps only if the background radiative temperature is not equal to the item temperatures like with a clear sky.

If the sky is cloudy or low overcast then you may not be able to see/detect the temperature difference.

Additionally, the emissivities of ice and water vary with angle. For example, see sea water

Emissivity of the Ocean | The Science of Doom
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Old 07-11-2014, 12:44   #54
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Re: Northwest Passage - 2014

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The two items with differing emissivities will show up at different apparent temps only if the background radiative temperature is not equal to the item temperatures like with a clear sky.

If the sky is cloudy or low overcast then you may not be able to see/detect the temperature difference.

Additionally, the emissivities of ice and water vary with angle. For example, see sea water

Emissivity of the Ocean | The Science of Doom
Why do you talk about detecting a temperature difference? We're not talking about the colour thermal cameras that would show red water and blue ice. Those have multiple CCD sensors tuned to pick up different IR bandwidths and then display faux colour based on the wavelength differences.

What we're talking about is a black and white camera that shows only a single, broad bandwidth of IR light. What it sees is how many IR photons hit the CCD sensor, not what frequency the photons have (assuming that they are within the bandwidth of the sensor, of course).

So if I have a 0C iceberg with an emissivity of 0.5 sitting in 0C water with an emissivity of 0.2 and with 0C clouds behind it with an emissivity of 0.1, I'll see a bright iceberg in darkish water with darker clouds behind it.
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Old 07-11-2014, 13:00   #55
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Re: Northwest Passage - 2014

After some google work, it seems that I got it wrong about the colour images that you can see from thermal cameras. It looks like they don't use multiple pixels for different wavelengths, they are making an assumption of constant emissivity and then showing intensity as different colours.

Anyways, I also found this link about using IR cameras to detect icebergs. It seems pretty definitive to me: Ice Detection and Ice Observation with Thermal Imaging
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Old 07-11-2014, 13:19   #56
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Re: Northwest Passage - 2014

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Originally Posted by cwyckham View Post
Why do you talk about detecting a temperature difference? We're not talking about the colour thermal cameras that would show red water and blue ice. Those have multiple CCD sensors tuned to pick up different IR bandwidths and then display faux colour based on the wavelength differences.

What we're talking about is a black and white camera that shows only a single, broad bandwidth of IR light. What it sees is how many IR photons hit the CCD sensor, not what frequency the photons have (assuming that they are within the bandwidth of the sensor, of course).

So if I have a 0C iceberg with an emissivity of 0.5 sitting in 0C water with an emissivity of 0.2 and with 0C clouds behind it with an emissivity of 0.1, I'll see a bright iceberg in darkish water with darker clouds behind it.
My friend you are in my wheelhouse now. In the focal plane of your IR imaging system is an array of detectors that detect energy in a continuous band of wavelengths between either 3 to 5 or 8 to 12 micrometers. I am assuming 8-12 although it doesn't matter. Each detector corresponds to each pixel in the display.

The sensor/detector sees the sum of the thermal emission from the surface it is looking at. That emission is a function of it's physical temperature and the reflection of the background emissions. Where the energy from the background is a function of it's temperature and emissivity.

So if the emissivity of the surface is 0.5 the sensor sees half of the self emission plus half of the reflection from background.

If the radiative power or temperature of the surface and the radiative power or temperature of the background is the same then it doesn't matter what the emissivity of the surface is, the radiative power leaving the surface and incident on the detector will be unchanged no matter what the emissivity of the surface is. Higher emissivity is more self emission and less reflection. Lower emissivity is less self emission and more reflection.

Consequently, two objects with the same temperature but differing emissivities will be the same gray level or color (if a color display) in the thermal imager if the background they are reflecting is the same temperature. This example is a special case of basic radiative transfer in a scene.
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Old 07-11-2014, 14:44   #57
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Re: Northwest Passage - 2014

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My friend you are in my wheelhouse now. In the focal plane of your IR imaging system is an array of detectors that detect energy in a continuous band of wavelengths between either 3 to 5 or 8 to 12 micrometers. I am assuming 8-12 although it doesn't matter. Each detector corresponds to each pixel in the display.

The sensor/detector sees the sum of the thermal emission from the surface it is looking at. That emission is a function of it's physical temperature and the reflection of the background emissions. Where the energy from the background is a function of it's temperature and emissivity.

So if the emissivity of the surface is 0.5 the sensor sees half of the self emission plus half of the reflection from background.

If the radiative power or temperature of the surface and the radiative power or temperature of the background is the same then it doesn't matter what the emissivity of the surface is, the radiative power leaving the surface and incident on the detector will be unchanged no matter what the emissivity of the surface is. Higher emissivity is more self emission and less reflection. Lower emissivity is less self emission and more reflection.

Consequently, two objects with the same temperature but differing emissivities will be the same gray level or color (if a color display) in the thermal imager if the background they are reflecting is the same temperature. This example is a special case of basic radiative transfer in a scene.
Oooh, your wheelhouse is fun! Thank you for the very detailed description. That makes perfect sense.

So in a perfect experiment of clouds, ocean and iceberg at the exact same temperature, I now fully understand what you're saying and why the emissivity cancels out.

In a practical scenario, though, the temperatures are never the same, of course. Even if the water and ice were theoretically the same, the sky would be different and the top surface of the ice would be thermally interacting with the sky and be at a different temperature than the rest.

How often in the real world would the sea water be at exactly 0C? How different would it need to be before a difference could be seen on the screen?

The stills and video in the FLIR video were pretty impressive.
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Old 07-11-2014, 17:37   #58
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Re: Northwest Passage - 2014

How often the sea 0, or -1 or whatever is a function of where you are. In that photo I posted above the water was 0C my air thermometer read 40F. I don't know the temp of that mist in the air, but it was f'ing COLD!

The temp of the Labrador current, which I was in will be right at -1.

I mean, essentially you have a bowl of water with ice cubes melting in it. It's all the same temp.
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Old 07-11-2014, 17:53   #59
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Re: Northwest Passage - 2014

Also, all this nice theoretical stuff aside, it's not like you are flying overhead looking down with a clear view. You are looking at an angle, a small angle along the water, with waves. The waves both hide the ice and wash over the ice. Obviously when they are hidden they are hidden, but when the water washes over you will read the water temp. So what percentage of the time are you actually looking at a growler.

Remember, the bergs are not your problem, it's the bergy bits and growlers. Imagine a pile of 7lb ice blocks, 10 blocks long, 10 wide, 2 high. That's 1,400lbs. Imagine that in the water, riding on top of the water, like a raft. That's not a real big target to see at a couple of hundred yards. It is presenting a washed edge, with water sloshing over, when it's not behind a wave. You need to see it at some distance simply because no one has the concentration to stare intently at a screen for more than a few minutes.

Now imagine hitting that, but what you hit is about 10,000lbs, because of the mass under the water.

Yeah, a thermal imaging camera might be helpful, but it might give you a sense of false security.

I can't recall who but I read of a couple running into a berg, thunk! Simply because of some momentary distraction. And they knew the berg was there.
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Old 07-11-2014, 18:01   #60
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Re: Northwest Passage - 2014

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Labrador Current, surface oceanic current flowing southward along the west side of the Labrador Sea. Originating at the Davis Strait, the Labrador Current is a combination of the West Greenland Current, the Baffin Island Current, and inflow from Hudson Bay. The current is cold and has a low salinity; it maintains temperatures of less than 32° F (0° C) and salinities in the range of 30 to 34 parts per 1,000. The Labrador Current is limited to the continental shelf and reaches depths only slightly greater than 2,000 feet (600 m). Its volume of water transport varies between about 125,000,000 and 190,000,000 cubic feet (3,500,000 and 5,400,000 cubic m) per second and annually carries several thousand icebergs southwar
Labrador Current (current, Labrador Sea, North America) -- Encyclopedia Britannica
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