Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 07-11-2014, 18:34   #61
Registered User
 
avb3's Avatar

Cruisers Forum Supporter

Join Date: Jul 2010
Location: Florida/Alberta
Boat: Lippincott 30
Posts: 9,913
Images: 1
Re: Northwest Passage - 2014

Quote:
Originally Posted by hpeer View Post
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.
Don't forget ocean salt water freezes at 28F. Icebergs are fresh water, and the difference in temps is what you see.
__________________

__________________
If your attitude resembles the south end of a bull heading north, it's time to turn around.
avb3 is offline   Reply With Quote
Old 07-11-2014, 18:50   #62
Senior Cruiser
 
DeepFrz's Avatar

Cruisers Forum Supporter

Join Date: Mar 2006
Location: Winnipeg
Boat: None at this time
Posts: 7,930
Re: Northwest Passage - 2014

The internal temperature of icebergs is much lower than 0 deg. c. and as the FLIR images show they show up very nicely on the screen.
__________________

__________________
The Blue Dot Campaign. This Changes Everything.
DeepFrz is offline   Reply With Quote
Old 07-11-2014, 18:53   #63
Senior Cruiser
 
hpeer's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: Philadelphia
Boat: Murray 33-Chouette & Pape Steelmaid-44-Safara-both steel cutters
Posts: 3,899
Re: Northwest Passage - 2014

Ok, in my example the water was 32f, bergs are fresh water at...32f.

No difference.

Look, I'm not saying it is of NO use, I'm saying that there are conditions when it likely will not work.

Also I went to the FLIR advert site and looked at their video. Although they SAY it works in rough weather they showed no conclusive evidence.

They showed lots of pics of big bergy bits at distance in calm water, and close ups of smaller bits. But none of growlers at any kind of distance or in even moderately rough sea, nothing with recognizable white caps.

That makes me skeptical.
__________________
hpeer is offline   Reply With Quote
Old 07-11-2014, 18:57   #64
Senior Cruiser
 
hpeer's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: Philadelphia
Boat: Murray 33-Chouette & Pape Steelmaid-44-Safara-both steel cutters
Posts: 3,899
Re: Northwest Passage - 2014

Quote:
Originally Posted by DeepFrz View Post
The internal temperature of icebergs is much lower than 0 deg. c. and as the FLIR images show they show up very nicely on the screen.
I'm sure icebergs do. They show up on radar too.

What about a 10' diameter growler? In any kind of sea?
__________________
hpeer is offline   Reply With Quote
Old 07-11-2014, 18:59   #65
Senior Cruiser
 
DeepFrz's Avatar

Cruisers Forum Supporter

Join Date: Mar 2006
Location: Winnipeg
Boat: None at this time
Posts: 7,930
Re: Northwest Passage - 2014

Quote:
What about a 10' diameter growler? In any kind of sea?
I guess we could both speculate on that but I really don't know.
__________________
The Blue Dot Campaign. This Changes Everything.
DeepFrz is offline   Reply With Quote
Old 07-11-2014, 19:08   #66
Registered User
 
SailOar's Avatar

Join Date: Jul 2011
Location: USA
Posts: 629
Re: Northwest Passage - 2014

Quote:
Originally Posted by LakeSuperior View Post
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.
I don't pretend to understand these technical arguments but in the link mentioned above by cwyckham they assert that ice and seawater of the same temperature will appear different.

Quote:
Most of the ice in the sea surrounding Greenland originates from glaciers and therefore mostly consists of fresh water. The exact emissivity differs slightly depending on the circumstances, but generally speaking fresh water has a higher emissivity than the salty sea water. This means that even if the temperature of the ice and the seawater are the same temperature, there will still be a contrast between the two in the thermal image. Another factor is the movement of the surface. The surface of the seawater is ever moving, rippling and churning, while the surface of the ice is solid, still. Even when the amount of thermal radiation emitted to the thermal imaging camera is more or less the same, which means that the ice and the water have more or less the same color in the thermal image, the ice will stand out in the thermal image due to this difference.
__________________
SailOar is offline   Reply With Quote
Old 07-11-2014, 19:13   #67
Senior Cruiser
 
hpeer's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: Philadelphia
Boat: Murray 33-Chouette & Pape Steelmaid-44-Safara-both steel cutters
Posts: 3,899
Re: Northwest Passage - 2014

Quote:
Originally Posted by DeepFrz View Post
I guess we could both speculate on that but I really don't know.
Yes, nor do I. But it would be really NICE to know.

I take you have sailed with bergs?
__________________
hpeer is offline   Reply With Quote
Old 07-11-2014, 19:43   #68
Senior Cruiser
 
DeepFrz's Avatar

Cruisers Forum Supporter

Join Date: Mar 2006
Location: Winnipeg
Boat: None at this time
Posts: 7,930
Re: Northwest Passage - 2014

Quote:
I take you have sailed with bergs?
No, thank goodness. Most of my sailing was on the West Coast of BC.
__________________
The Blue Dot Campaign. This Changes Everything.
DeepFrz is offline   Reply With Quote
Old 07-11-2014, 21:41   #69
JRM
Registered User

Join Date: Aug 2009
Location: Santa Barbara
Boat: Valiant 40
Posts: 416
Images: 2
Re: Northwest Passage - 2014

Quote:
Originally Posted by hpeer View Post
Yes, nor do I. But it would be really NICE to know.

I take you have sailed with bergs?
I did the ice bucket test. Because it's a very small world, I'll be paddling with an engineer from a major thermal imaging company tomorrow morning. I'll ask him about the ice berg question. If anyone would know, he will.

JRM

Sent from my SAMSUNG-SM-G900A using Cruisers Sailing Forum mobile app
__________________
JRM is offline   Reply With Quote
Old 07-11-2014, 22:46   #70
Registered User
 
LakeSuperior's Avatar

Join Date: Jan 2008
Boat: Teak Yawl, 37'
Posts: 1,581
Images: 7
Re: Northwest Passage - 2014

Quote:
Originally Posted by SailOar View Post
I don't pretend to understand these technical arguments but in the link mentioned above by cwyckham they assert that ice and seawater of the same temperature will appear different.
That would be my conclusion also. That is because of the cold sky in the infrared. In this case the sky thermal radiation that is reflected by the ice is generally much colder than the radiation emitted by the ice or liquid water.
__________________
LakeSuperior is offline   Reply With Quote
Old 08-11-2014, 07:04   #71
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2005
Boat: Outbound 44
Posts: 4,580
Re: Northwest Passage - 2014

Quote:
Originally Posted by LakeSuperior View Post
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
If the items have different emissivity, then they have different reflectivity. In practice in an environment like sea, clouds and ice I'd expect there to be enough radiation difference to stand out on a FLIR display. Fog does tend to block the IR.
__________________
Paul L
http://svjeorgia.blogspot.com
Paul L is offline   Reply With Quote
Old 09-11-2014, 15:39   #72
JRM
Registered User

Join Date: Aug 2009
Location: Santa Barbara
Boat: Valiant 40
Posts: 416
Images: 2
Re: Northwest Passage - 2014

Spoke to the engineer yesterday, and had him put it in layman's terms as much as possible.

The practical answer is yes, it works well. They do a lot with application specific wavelength filters, and have played around with this exact scenario. At one point, software for auto recognition was developed, but then not marketed. Their design market in this space was for larger commercial vessels that could better afford the technology and were watching for larger bergs.

JRM

Sent from my SAMSUNG-SM-G900A using Cruisers Sailing Forum mobile app
__________________
JRM is offline   Reply With Quote
Old 11-05-2015, 19:53   #73
Senior Cruiser
 
DeepFrz's Avatar

Cruisers Forum Supporter

Join Date: Mar 2006
Location: Winnipeg
Boat: None at this time
Posts: 7,930
Re: Northwest Passage - 2014

Sea level rise accelerated over the past two decades, research finds.
Apparently there was a glitch in software that had indicated that sea level rise had slowed in the 90's.
Sea level rise accelerated over the past two decades, research finds | Environment | The Guardian
__________________
The Blue Dot Campaign. This Changes Everything.
DeepFrz is offline   Reply With Quote
Old 11-05-2015, 21:42   #74
Senior Cruiser
 
StuM's Avatar

Cruisers Forum Supporter

Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43
Posts: 6,712
Re: Northwest Passage - 2014

Quote:
Originally Posted by DeepFrz View Post
Sea level rise accelerated over the past two decades, research finds.
Apparently there was a glitch in software that had indicated that sea level rise had slowed in the 90's.
Sea level rise accelerated over the past two decades, research finds | Environment | The Guardian
Incredible:
"Watson’s team found that the record of sea level rise during the early 1990s was too high. ...The results revise downwards the average rate of sea level rise since the 1990s. The IPCC’s landmark report in 2013 found the sea had risen on average by 3.2 mm per year since 1993. Waston’s study found the rate was slightly slower, between 2.6 and 2.9 mm per year."

So SLR is now thought to be only 85% of that previously calculated. And that gets spun into more gloom and doom by the Grauniad.

__________________
StuM is offline   Reply With Quote
Old 11-05-2015, 22:01   #75
Senior Cruiser
 
DeepFrz's Avatar

Cruisers Forum Supporter

Join Date: Mar 2006
Location: Winnipeg
Boat: None at this time
Posts: 7,930
Re: Northwest Passage - 2014

But the story is about the RATE of sea level rise Stu. The RATE is increasing.
__________________

__________________
The Blue Dot Campaign. This Changes Everything.
DeepFrz is offline   Reply With Quote
Reply

Tags
passage

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cruising the Pacific Northwest and Alaska's Inside Passage Divtruk Powered Boats 34 13-06-2017 12:44
Crew Available: Female Offshore Yachtmaster wanting to do Northwest passage 2014 jobreen Crew Archives 3 05-06-2014 13:00
Fiona Completes the Northwest Passage. anotherT34C Cruising News & Events 7 22-09-2009 14:12
Northwest Passage Colorado Dreamer Polar Regions 22 01-09-2008 13:05
The Northwest Passage is OPEN FOR BUSINESS ssullivan General Sailing Forum 0 13-09-2007 17:09



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 03:35.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.