The Rapids of the Drowned

Well, I was out of province for a couple weeks, but am back now. Time for some regular updates.

Fort Smith, in the Northwest Territories, lies right on the Alberta Border.  With about 2500 residents, it’s a small town(of course, every community in the Northwest Territories other than the capital of Yellowknife is a small town if it is considered ‘big’). It is on the main route into Wood Buffalo National Park, which covers almost 45 000 km² and is one of the largest parks in the world(but more about the park another time).

Fort Smith lies on the Slave River, beside the last of the major rapids on the river. Called the Rapids of the Drowned, these rapids are extremely wide, flowing over the Canadian Shield. The River is extremely dangerous and unpredictable at this point, with the rapids ‘s difficulty being rated anywhere between 1(easy) and VI (impassable). The origin of the name is best described from the sign above the river trail:

The other noteworthy thing about the river is that it is home of the northernmost American Pelican colony; every spring, they migrate up to the Slave River to breed. Actually, depending on the time of year, Pelicans aren’t that unusual in Canada; I’ve also seen them in Alberta and Saskatchewan, and know that they nest in British Columbia as well. At the time I visited, they were on the far side of the river, so I never had much chance for closeups, only long distance photos.

These pictures were all taken in the afternoon right on the banks of the Slave River. With a lower water level, I was able to walk out on the bedrock up to the water’s edge.

Above the large rapids on the left, there is a larger group of pelicans; a few single pelicans are visible further upriver. The above photo is the one I’ll be using to compare different spectra, so here it is broken down into the Blue, Green, and Red colour channels.

These three channels are all fairly similar this time. The sky darkens slightly as the wavelenghth increases from blue to red, and the trees and rocks lighten a bit, but there isn’t the haze present in many of my other photos. The pelicans are just as bright in all three photos.

Using my Zomei 680 nm filter, I can cut out the blue and green channels. This filter is deep red to the naked eye, and also allows infrared light in. It’s close enough to the visible range, though, that colour differences are still detectable by the camera. Using a white sheet of paper to set the white balance, the photo resolves to:

I like this filter for the colour it shows- the blue trees contrast the brown sky.  As I use filters deeper in the infrared range, the colours become more faded; becoming monochrome with the 850 nm filter. I skipped all the intermediate infrared filters at this location, and only took a photo with my deepest infrared filter, a Zomei 950 nm filter. Here is the Rapids of the Drowned as seen at that range.

The sky and water are much darker at that level of infrared, almost black. This photo was taken at an angle slightly to the left of the previous ones; the large group of pelicans are on the right side of the photo here.

Now,  I also took a full spectrum photo- this is my camera’s default spectra without filters. With the normal filters removed from my Canon Rebel t3i, infrared and ultraviolet light are detectable by the sensors. The camera is not very sensative to UV light, though, so the main result is that mainly the infrared light changes the photo.

The sky is slightly brighter, due to the ultraviolet light,  but the main difference is that the trees have turned brown. The infrared light is defined by the camera as part of the red channel. As trees strongly reflect infrared light,  the camera interprets the data as them being much redder than in real life.

Now, to cut out visible light entirely, but allow infrared an ultraviolet light in, I use my Schott UG11 filter. It allows ultraviolet light inf from 300 to 400 nm, peaking at about 350 nm, and a small amount of infrared light in at 750 nm. because my camera is less sensitive to UV light, however, infrared light is a major component of the final picture.

The sky is a dark violet; the infrared darkens the sky while the ultraviolet lightens it. The trees are faintly green, but still very light from the infrared readings. I haven’t found many practical uses for this filter yet, but enjoy the results of the photos.

Finally, I’ve mentioned before that I don’t often take true ultraviolet photos. As I mentioned, my camera isn’t very sensitive to that range, so I have to either take very long exposures, or boost the ISO range. Still, this is one of the places where I do have an ultrviolet photo. Combining the Schott UG11 filter with a Schott BG40 filter allows me to cut out almost all the infrared light(I’ve read there might be minute leakage of IR light) and all visible light, leaving only the Ultraviolet light. in ultraviolet, this is the view of the Rapids of the Drowned:

Well, the pelicans are still visible, but …yeah, there’s another reason I don’t often take UV landscape pictures. They just don’t look very good. It might be my skills or the camera, but from what I’ve read, it might be a more fundamental issue. Reyleigh scattering is why the sky is blue, and why haze seems to make distant objects blueish. the atmosphere scatters light with shorter wavelengths- the blue light from the sun scatters in the atmosphere, and comes at you from all directions.  for distant objects, the blue light is coming at you from in front of the object. I mentioned before that infrared light is great at cutting through haze; Ultraviolet light is the opposite.  Ultraviolet light has an even shorter wavelength than blue light, and is scattered much more.

All of my Ultraviolet photos have several features in common. The sky is extremely bright compared to the ground, due to the scattering, and distant objects always look very hazy. For some of my pictures, having the photo bright enough to see solid objects means that the sky is pure white and washes out the background, so I usually shoot in RAW for the extra detail. I still take UV landscapes, however; it’s more out of curioisity than any hopes for a good photo. I just like to explore outside the visible range of normal cameras.

So in conclusion… the Rapids of the Drowned are very pretty, but don’t swim in them, and the only thing that stays bright in all the wavelengths tested are the pelicans. I don’t know if that’s a life lesson you can apply in other circumstances, so make of it what you will.

The photos were taken with a Canon Rebel t3i camera.