Looking Through False Coloured Glasses
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.