Look­ing Through False Coloured Glasses

Cape Bre­ton­weather

The Victoria Standard - - WEATHER - BILL DANIEL­SON

We’ve just made it through sev­eral weeks of rugged weather. I imag­ine no one wants to be re­minded yet again how deep the snow was, how strong the winds blew, how long the power was out, and how many no-schoolies we’ve had. We all know the num­bers are large.

So let’s take a dif­fer­ent view of our weather. Here’s a satel­lite im­age of Cape Bre­ton and vicin­ity, taken a few days ago. The par­tic­u­lar date and time are not cru­cial; sim­i­lar images come tum­bling down from the satel­lite ev­ery day, and of­ten the pat­terns are sim­i­lar to this one.

At first glance, it looks like the Mar­itimes are on fire. “Hold on,” I hear you say­ing, “Surely global warm­ing hasn’t pro­gressed this far!”

You’re right -- we’re not about to burst into flames. An as­tro­naut gaz­ing down on the Mar­itimes from space would not see all that red, orange and yel­low. In fact, right now she would see very lit­tle colour at all. Re­gions of open wa­ter, and conif­er­ous forests, would look black. Nearly ev­ery­thing else, from clouds to snow, ice, sand, smoke, and bare ground, would look white or grey.

On the other hand, the false colour im­age shown here is a riot of hues. To cre­ate it, the satel­lite shot three images of the same area, one in blue light and two in in­frared “colours” which are in­vis­i­ble to the hu­man eye. The two in­frared images were then com­puter-mapped as red and green, and com­bined with the blue im­age, pro­duc­ing the false colour im­age you see here.

The rea­son for all this fid­dling around is that in­frared light in­ter­acts dif­fer­ently with dif­fer­ent ma­te­ri­als. For ex­am­ple, snow and ice cover have a dis­tinct in­frared sig­nal, which is mapped as red. So Prince Ed­ward Is­land, New­found­land, and An­ti­costi Is­land, all of which are snow cov­ered, ap­pear red. Same with the ice cov­ered re­gions of Northumberland Strait and the Bay of Chaleur. Mean­while, the Gaspé, coastal New Brunswick, main­land Nova Sco­tia and Cape Bre­ton’s Rich­mond County also show red (snow cover), but it is mixed with vary­ing amounts of black, due to the pres­ence of spruce forests. As you can see, this dif­fer­ent tex­ture makes it easy to dis­tin­guish coastal ice from snow-cov­ered land.

Clouds send a dif­fer­ent in­frared sig­nal, which is mapped in white or yel­low in this im­age, de­pend­ing on whether the cloud par­ti­cles are wa­ter droplets or ice crys­tals. No­tice how easy it is to dis­tin­guish them from ice and snow cov­ered ground, a dif­fi­cult task if you’re work­ing with a true-colour im­age where ev­ery­thing looks white and grey.

Many fea­tures in this im­age are typ­i­cal of win­ter days in the Mar­itimes and Cape Bre­ton in par­tic­u­lar. You can ac­tu­ally see the pre­vail­ing north­west­erly wind flow, thanks to the clouds. I love the way they snake out of north­ern bays and val­leys, grow as they pick up mois­ture and heat from the wa­ters of the un­frozen Gulf, and rush to­wards Cabot Strait. As they grow they com­bine to form larger cells, and their colour be­comes more yel­low – ev­i­dence that they are grow­ing ver­ti­cally, be­com­ing colder, turn­ing to ice and snow, and get­ting ready to pre­cip­i­tate.

And then the winds col­lide with Cape Bre­ton! Our is­land com­pletely re­shapes the clouds into bands aligned along the High­lands. The col­li­sion takes its toll on the clouds’ en­ergy and mois­ture, leav­ing Vic­to­ria and In­ver­ness Coun­ties deeper in snow pack, but Rich­mond County and the off-shore wa­ters cloud­free.

Mean­while, you can see that main­land Nova Sco­tia and PEI ex­pe­ri­ence a very dif­fer­ent win­ter day. The north­west winds tra­verse very lit­tle open wa­ter, so clouds do not form, leav­ing res­i­dents with mo­not­o­nous hours of sunny skies.

I con­fess, I love this im­age. I have stud­ied it for hours and love it for the vol­umes of in­for­ma­tion that it con­tains. But I love it even more for its ex­quis­ite pat­terns, colours, tex­tures, and ac­tion! I hope you un­der­stand my fas­ci­na­tion and you feel a lit­tle bit the same.

False colour im­age from NASA’S Terra/modis satel­lite taken 11 Fe­bru­ary 2017. 1-Cape Bre­ton; 2-PEI; 3-Northum­ber­land Strait; 4-New­found­land; 5-An­ti­costi I; 6-Bay of Chaleur; 7-Gaspé.

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