My four companions at Atigun Pass (from left: Simon, Philip, Art and Chris).

Figure 1. My four companions at Atigun Pass (from left: Simon, Philip, Art and Chris).

April 8th, 2012: I had somehow missed that we were leaving on Easter Sunday…. but the drive North across Alaska and the Brooks Range on a perfect day, clear blue skies, pristine white snow, and majestic mountains, was ample compensation for leaving town on a holiday, and my four companions (Fig. 1) did not seem to mind.

We five are the advance team for a campaign to measure the snow cover of the North Slope of Alaska. The snow cover (Fig. 2) here lasts 8 months of the year, and it is important for several reasons. First, somewhere between 50% and 80% of the run-off in the rivers in this part of Alaska come from snow melt alone. Second, the snow is an effective insulator that keeps the ground from freezing even more deeply during the winter than it does now. Without the snow the permafrost here might be thicker, the summer thawing active layer thinner, and the plant life less verdant. Third, the snow is a wonderful reflector of solar energy (it has a high albedo, reflecting about 85% of the light that hits it), which effectively keeps Northern Alaska cooler in the winter and early spring than it might otherwise be. If it seems like these last two are contradictory, you are right. There is a fine balance between the insulation effect and the solar reflecting effect of snow, and this balance plays a critical role not only in the climate of the Arctic, but also of the entire planet. So in short, in a place like Northern Alaska, snow matters, and we had come to measure its properties.

Snow blankets the slopes of an unnamed mountain south of Atigun Pass. Notice the drifts. (C. Polashenski photo).

Figure 2. Snow blankets the slopes of an unnamed mountain south of Atigun Pass. Notice the drifts. (C. Polashenski photo).

More precisely, we have come to see if we could develop a more effective way of measuring snow depth. Snow depth can be easily measured by pushing a ruler down through the snow, and if the snow cover were smooth and even blanket, a few measurements here and there would be enough to tell us about the regional snow cover, but the snow cover of the North Slope is anything but even and smooth. Wind drifts the snow incessantly, creating drifts and scour zones. In the space of 100-m one can measure depths ranging from 10 cm to 500 cm. Even with GPS-enabled special ruler probes (more on these in a later blog) it is not possible to map out the snow by hand.

Many other methods of measuring snow depth have been tried: Mono-pulse and FM-CW radars on sleds and helicopters, passive and active microwave transmitter/receivers on sleds, aircraft and satellites, gamma-ray detectors on aircraft, and even satellite borne gravimeters.

To date there have been some successes, but really no operational quality methods have emerged that work for all types of snow, and the problem has been especially acute for snow that tends to be thin (<100 cm in general) like the snow of the North Slope of Alaska.

However, the recent development of scanning LiDAR (Light Detection And Ranging) equipment may be the game-changer. Mounted on an aircraft looking downward, one of these scanning devices can create a swath map of the snow surface with near centimeter precision. If a second map of the exact same area is acquired when there is no snow, the two surfaces can be differenced to produce a snow depth map. DGPS (Differential Global Positioning Systems) make this precise co-registration possible.

An oil rig near Prudhoe Bay, Alaska.

Figure 3. An oil rig near Prudhoe Bay, Alaska.

In principle, all this could be done with sufficient accuracy to produce useful and reliable snow maps, but is it possible in practice? That’s why we were driving North on Easter Sunday. And this snow depth problem is not simply academic. The State of Alaska and the Federal Government manage thousands of square kilometers of land on the North Slope and have to make decision where and when oil, gas and mining companies can be allowed to transit over the tundra. Open the tundra too soon with too little snow cover and the tundra will be damaged; open it too late and the companies may not be able to effectively explore for or develop strategic deposits (Fig. 3).

We have been preparing for the campaign for months, and had been packing for days. In addition to our advance team, 7 more people will be coming in at the end of this week to help make the thousands of ground-based measurements we will need to check the accuracy of the airborne LiDAR products. The aircraft will be coming a week from now.

Today, we are driving two rigs north pulling snowmobile trailers. Our pickup and the SUV were packed full, and on the trailers were three snowmobiles, four plastic sleds, and a special sled for a ground-based LiDAR (more on this later too). Everything was covered over because we were expecting a muddy trip.

We left Fairbanks at 8:30 AM. From Fairbanks, the first part of the trip (245 km) is through the spruce- and birch-covered hills of the Yukon Tanana uplands along the Elliot Highway. Next it follows the Dalton Highway, which runs through the Brooks Range at Atigun Pass (Fig. 4).

Figure 4: Looking north from Atigun Pass. Art and Philip are in the truck and trailer in front of us. (C. Polashenski photo).

Figure 4: Looking north from Atigun Pass. Art and Philip are in the truck and trailer in front of us. (C. Polashenski photo).

The latter is also know as the Haul Road, as it was built in order to haul materials north during the building of the Trans-Alaska Pipeline. The Dalton is steeper than normal highways, much of it is dirt (or used to be), and it is mainly transited by truckers headed to the oilfields of Prudhoe Bay.

For those who watch Ice Road Truckers (Season 3), it details the tribulations of the truckers along this stretch of road… and exaggerates them considerably. Personally, I think I have driven over Atigun Pass more than 40 times in winter, and while it requires care, it is more beautiful than dangerous.

Several hours of driving brought us to the Yukon River. During the Gold Rush in the Klondike (1898), and for the next 40 years, this great river was the main highway for the Alaska and Yukon Territory, plied by paddle-wheel steamers.

Figure 5: The bridge over the Yukon River (note the semi headed south…the main traffic on the road. (C. Polashenski photo).

Figure 5: The bridge over the Yukon River (note the semi headed south…the main traffic on the road. (C. Polashenski photo).

Now it is bridged by an unusual downhill sloping bridge (Fig. 5) built during the pipeline construction, and it is pretty quiet. In September, moose hunters will come here to launch their boats, but the rest of the year boat travelers would have the great river pretty much to themselves.

The trip started to get more exciting as the Brooks Range came into view. We always gas up at Coldfoot (Fig. 6), which to me marks the south edge of this great mountain range. Coldfoot was founded in around 1902 as a gold mining town. Legend has it that miners who had penetrated this far got “cold feet” and turned back south, fearing the on-coming winter and slow starvation.

Figure 6: Coldfoot Camp.

Figure 6: Coldfoot Camp.

Many years later, the famous Iditarod musher Dick Mackie founded the truck stop/café/tourist attraction that still exists today. Lots of visitors come through here in the summer because it is a jumping off place for trips into the Brooks Range. Not far away is the other old gold mining town of Wiseman, made famous by the writings of Bob Marshall (Fig. 7). Marshall came into the country in 1929 and made a series of long camping and exploring trips in the Brooks Range (both summer and winter).

At that time Wiseman was about as remote as any place in the world. He was intrigued with the idea of “wilderness”, and utterly charmed by the society of white miners and Inupiat inhabitants he found living in harmony in around Wiseman. His two books….both excellent reading….are Alaska Wilderness and Arctic Village. His ideas of wilderness and the place of wildness in society still have impact today.

Figure 7: Bob Marshall (4th from left)

Figure 7: Bob Marshall (4th from left)

From Coldfoot we wound through the Brooks Range following the Koyukuk River drainage toward its head, passing Sukapak (Fig. 8 ) and Snowden Mountain and climbing up on to the Chandalar Shelf.

Here the wildlife became spectacular….hundreds of caribou (Fig. 9) grazing near the road, ptarmigan in full white winter plumage (Fig. 10) enjoying the sunny day out on the tundra, and even some Dall sheep. From the Shelf, we continued climbing up to the Pass at 4739’ (1444 m). When I was a student first starting to work on snow on the North Slope, my mentor and friend Dr. Carl Benson would always stop here at the summit and talk about how the Brooks Range was one of the great climatic divides of the world, separating the taiga forests from the cold boreal tundra.

Today the Pass was living up to its reputation: to the south the roads had been muddy and the air temperature above freezing. To the north the temperature was well below freezing, the road snow covered, and stiff wind was blowing.

Figure 8: Sukapak Mountain (C. Polashenski photo).

Figure 8: Sukapak Mountain (C. Polashenski photo).

Feeling the weight of Dr. Benson’s lessons, I briefly announced to my companions that this was a “great climatic divide”, then we got back in our rigs and descended the steep north side of the pass with great care. Another 45 minutes of driving and we arrived at the Toolik Lake Field Station.

The camp was quiet, and as always, we received a warm welcome. We unloaded our gear, rolled out our sleeping bags in the bunk houses, and started thinking about the campaign to come.

Figure 9: Caribou near the road (C. Polashenski photo).

Figure 9: Caribou near the road (C. Polashenski photo).Figure 10: Ptarmigan enjoying a sunny day on the tundra (C. Polashenski photo).

Ptarmigan (C. Polashenski photo).

Ptarmigan (C. Polashenski photo).

Figure 11: The long road North (C. Polashenski photo).

Figure 11: The long road North (C. Polashenski photo).

Tomorrow: Setting up a control network on the Arctic Tundra.

Figure 12: Not only gangsta’s have spinners!

Figure 12: Not only gangsta’s have spinners!