On 28 October, 1957, our five-man party left Ellsworth with two Sno-Cats (the other U.S. IGY traverses had three or four) each pulling a 2.5-ton sled filled with fuel, food, explosives-, and all of our scientific and other equipment. For the next 81 days we made a geophysical-glaciological reconnaissance of the Filchner-Ronne Ice Shelf area, and made the first geologic observations of the Dufek Massif.
I put in my first magnetic station near Ellsworth and we then headed southeast, taking gravity, magnetic, and altitude observations every 8 km (Fig. 6-4). We used the gravity and magnetic measurements to study the variations in density and magnetic properties of rock beneath the ice, and therefore to make inferences about the ice-covered geologic features. We also used the gravity data to determine the depth to bedrock between the seismic reflection stations.
This is possible because the rock is much denser than the ice or water. The lower the gravity, the deeper the bedrock. We had a radio in each vehicle, and the drivers were in constant contact using headphones to hear over the roar of the engines and the clatter of the vehicle tracks.
Figure 6-4: Traverse at intermediate station. Behrendt reading magnetometer at left. Walker and Aughenbaugh making snow hardness measurement left background. Thiel on track of Sno-Cat after making a gravity measurement. Crevasse detector visible on lead vehicle (Photograph by John Behrendt).
The logistics of our traverse were dictated by the fact that state-of-the-art elect-ronics at the time depended on the vacuum tube, rather than the solid-state electronic microcircuits available today. The hundreds of tubes in our seismic system required large amounts of battery power produced by two 250 amp-hour truck batteries weighing 80 kg each. The only recording system was the heavy oscillograph "camera" with its tanks of photographic solutions (Fig. 6-5).
Figure 6-5: Behrendt operating seismic reflection equipment mounted inside Sno-Cat (Photo-graph by John Behrendt).
Altogether the seismic Sno-Cat carried a total load of about 500 kg of electronic equipment, gravimeter, magnetometer and seismic batteries. Counting the weight of two people in the vehicle, we carried about the maximum allowable load. Each Sno-Cat used about 3 l of fuel (gasoline) per km or about 200 kg for a 50km day for two vehicles. This fuel a little more than one barrel per day -would determine how frequently we needed resupply by the two available
single-engine Otter aircraft. These planes could only carry a few barrels of gas in one trip depending on our range out of Ellsworth. Their maximum allowed range was only 460 km from the base, although they exceeded this limit on several occasions.
Unlike many Antarctic field parties today, we could not have used snowmobiles (which had not yet been developed) because of our heavy loads. There were two other significant reasons for using the high fuel-consuming Sno-Cats on the traverses. The first was safety. A Sno-Cat was the lightest snow-pressure vehi-cle available at that time, which proved very important in crossing crevasses.
Also, because we were a working scientific field party, not an adventure expedi-tion, any convenience in general camping greatly speeded up our progress. We slept in the Sno-Cats, so on a number of occasions when we had been up for 24 hours or more, it took less than a minute to crawl into a sleeping bag after stopping for the "night," or after downing a quick meal. Putting up and taking down Scott tents, commonly used by geologists in semi stationary Antarctic field camps today, would have been time consuming and inconvenient for a field party moving every day. This was particularly true when stopping in a storm or when surrounded by invisible bridged crevasses. Several years later, when I led a traverse with three vehicles, we traveled with one six kilometers ahead of the other two for barometric altimeter corrections.
Navigation over the course of a day's travel was by dead reckoning using the gyro compass mounted in the lead Sno-Cat, #1. A few years later the U.S.
traverses changed to magnetic compasses mounted in the Sno-Cats, which were an improvement because of the fragility of the gyro compasses. Despite the conventional wisdom, magnetic compasses work well in Antarctica, except possibly very close to the magnetic pole about 2000 km from our traverse area.
About every 40-60 km, Neuberg, our navigator, measured the exact position of the sun using a theodolite on a tripod. He determined the time with a chrono-meter that was checked with a time signal from the U.S. National Bureau of Standards radio station WWV, which we received well. He then calculated our position using a slide rule (pocket calculators did not exist) to better than 200 m accuracy using a nautical almanac. It was easy to steer a Sno-Cat in a straight line despite the weaving, which averaged out. Therefore, we could correct the dead reckoning positions of the 8-km spaced gravity and magnetic stations along our route, every day that we stopped for station work, using the accurate position obtained from the sun shots.
Steering the Sno-Cats on a planned course, with compasses and odometers, was amazingly accurate. In 1960-61 I navigated by dead reckoning to poles left by an earlier traverse and later to a field camp in zero visibility caused by blow-ing snow. Unlike ships and airplanes, Sno-Cats did not drift sideways. Travelblow-ing at only 5-8 km per hour, they did not get very far off course in 8-12 hours.
We had no geographic information, so we used a blank gridded chart as does a ship plotting its position at sea. In this manner we mapped the course of our traverse and any features of the snow surface that we could observe. As our horizon was quite limited, the process somewhat resembled blind men attempt-ing to describe an elephant.