Wednesday, August 24, 2011

ARIANNA 2010 - Part 4 - Finale

Here is the conclusion of Jordan's account:

And then came the fog. The fog drifted in from the south and obscured the helo pilot's ability to see where he was landing. After several unsuccessful attempts to descend through open patches, the pilot decided to return to McMurdo and try again the next day. Then, we saw from a distance, the helo descend through a patch of fog that had opened. The helo returned, 50 meters off of the ground, and dramatically landed right next to our camp in a whirl of snow and cheers. Although I looked forward to warm food and a hot shower back at the main base, I felt the Antarctic wilderness calling me back. I admired its raw untouched beauty as we ascended through the clouds above the glaciers, and looked back as our experiment disappeared in the distance.

The first flights leaving McMurdo were delayed, and it turned out we'd be spending Christmas in McMurdo. Steve and I had planned on this, and simply enjoyed the food and good company in the mess hall, which had quite a buffet for Christmas dinner. I also took the opportunity to hike to the top of Observation Hill, which looks out over McMurdo and the surrounding ice shelf.

After we drove to Pegasus air field, where our C-17 was supposed to embark for Christchurch, we met several physicists from the CREAM experiment. CREAM (Cosmic Ray Energetics and Mass) is an experiment designed to detect cosmic rays in the upper atmosphere by flying the detector on a balloon. We swapped stories from the field and took pictures. It was a fitting way to end the trip, in the company of fellow cosmic ray Antarctic researchers.

There has been a lot of activity since we returned to the USA. A paper on the results of our analysis of the reflecting properties of the ocean is going to be published in the proceedings of the 2011 International Cosmic Ray Conference. We are also gearing up for next season, and we plan on installing a second prototype station. We've added a new graduate student, Joulien Tatar, who is working on a way to link the two stations together via noiseless wireless communications. We are in the process of fabricating the circuit boards for the next station, which will include a new way of distinguishing the difference between an interesting neutrino-like signal, and radio noise.

Postscript from Spencer: Planning for the 2011 season is underway now.

ARIANNA 2010 - Part 3 - In the Field

Here is part3 of Jordan's account of the 2010 ARIANNA field season:

In addition to fixing the station, Steve and I also scheduled time to make measurements of certain properties of the ice beneath the detector. Spencer Klein and Thorsten Stezelberger had already calculated the depth of the shelf beneath the prototype using data taken in 2009. They did this by pulsing a radio signal down through the ice, and measuring the time for the signal to return after reflecting. This experiment requires very sensitive equipment, since the signal strength decreases with distance, and we're working with a total path length of over a kilometer. Steve and I repeated this measurement, and got the same answer as Spencer and Thorsten. We would also go on to use that data to measure how much power a radio wave loses as it travels through the Ross Ice Shelf. The key problem in the past was that no one knew how much power the radio wave looses when it reflects off of the ocean beneath the ice shelf.

To study this separately from the effect of the ice, I moved our transmitting equipment to the end of the 1 kilometer flag line we established on the first day of the expedition. I had the help of Leah Biezums, who flew in via helo to relieve Rebekah after the first week. Now we had a path length of one and a half kilometers, and the power loss from the ice would be stronger because of the increased distance the radio signals had to travel through the ice. Presumably, the properties of the reflecting ocean were the same. Thus, by comparing the amount of power received in the signals with different path lengths, but the same reflection properties, we could isolate and study the reflecting properties alone. We've found that the ocean/ice interface acts like a smooth mirror, reflecting a large fraction of the radio signals' power. This bodes well for detecting high energy neutrinos which create radio pulses, because neutrinos propagating downward through the ice shelf will create radio waves that reflect off of the bottom and back up towards the ARIANNA detectors.

As the expedition began to draw towards its close, Steve and I began to perform tasks that would ensure the viability of the detector throughout the rest of the summer and winter. We repositioned the “heartbeat” antenna, which is designed to pulse calibration signals at the prototype detector and tells us certain information about its ability to trigger on neutrinos and determine their direction. We chose a more ideal location based on heartbeat data taken the previous season. I later used this data to show that ARIANNA has the ability to distinguish the time of arrival of a signal in two different sensor antennas to a precision of 100 picoseconds. With Leah's help, I erected the larger, more powerful wind generator and watched as it begun to spin, providing sustainable power to the station which would eventually lead to data being taken further into the Antarctic winter. We began to pack up the gear, both survival and scientific, and awaited our helo extraction.

Monday, August 1, 2011

ARIANNA 2010 Part 2: Arrival in Moore's Bay

Here is part 2 of the guest post by Jordan Hanson, about the 2010 ARIANNA field season.

The beauty which surrounded us during our helo flight to the detector can only be inadequately described. We flew past windswept mountains covered in dark weather, accompanied by white glistening glaciers beneath. We observed rock formations and islands in the ice shelf that protruded upwards for a thousand feet, such as Minna Bluff. Finally, we passed Mount Discovery and proceeded onto the vast, open Ross Ice Shelf – a flat expanse of pristine snow-covered sea ice over half a kilometer thick. One hundred and twenty kilometers from our departure point, we located our detector.

After we touched down and the rotors of the helo stopped spinning, we began to unload the gear and set up camp. First we established a “cargo line,” a row of bags and tents that allowed us to access individual pieces of equipment easily in an environment in which it can be difficult to maneuver. We also had to scan for crevasses, potentially melted cracks in the ice that can have depths of hundreds of feet. With the help of ground penetrating radar, we were able to trace out a safe area on which we could safely build our camp. I remember it being so windy (in excess of 40 mph from the south) that my hands got numb each time I took them out of my parka pocket to take a bite of my sandwich.

Once we had constructed camp, we began cooking and boiling water to keep warm and get used to living there for two weeks. We had several tents: one for working and the kitchen, three tents for sleeping (Steve, Rebekah, and myself), and a tent which served as an outhouse. We unpacked our scientific gear and began installing it in the work tent. After we created our camp site, it was my job to establish a 1 kilometer flag line to be used in a later experiment. I went with a mountaineer from McMurdo, who examined the output of a ground-penetrating radar unit while I pulled it on a sled. Placing a bamboo flag every 100 meters, we staked out a crevasse-free line 977 meters long. Camp looked like a few yellow dots on a vast, flat white surface, backed by mountains covered with glaciers in the background. After placing the flags, we headed back to base.

I was eager to fix the detector, which had not come online yet since the sun had returned to shine on our solar panels. We had a small wind generator during the previous season, but it turned out not to draw enough power from the wind storms that happen every so often on the ice shelf. Steve injured his back the day we arrived in camp, so he returned to McMurdo for medical treatment while Rebakah mangaged the camp and I saw to the ARIANNA prototype. I had a satellite phone which I used to communicate with Thorsten Stezelberger, who installed the detector originally with Spencer Klein in the 2009-10 season. I noticed that the 12V lead-acid gel battery used to power the detector was cracked, having slightly frozen and expanded. However, it still held charge, and thus we do not expect that this was the problem.

It took us a long time to excavate the electronics box, which was buried in six feet of snow, beneath the metal rig that supports the solar cells. Once we had it in the tent, I used a Honda generator and a DC power source to power the electronics, while I checked each electronics component individually to located the problems. Before replacing anything, I extracted the data from the previous season and saved it on one of our computers and in other places. There was brand new event data that we had never seen before, since our station ran even after the wireless communications were removed. I replaced the CPU battery backup, which had lost its charge after so many months without power and in -30 degrees Celsius temperatures. I replaced the CPU itself, which appeared to be non-functional, and the analogue to digital converter (ADC) as well. After I fixed those components, I checked to see if the Iridium satellite modem began to draw current. I eventually figured out that the network settings such as port assignments had been lost and/or changed for certain systems upon shutdown, and after fixing all of that, the satellite modem began sending data North. Fixing the current prototype was a big victory for us, because it allowed us to take data during the 2010-11 season at a lower threshold, since man-made noise sources from the wireless communications equipment had been found and eliminated. In addition, I built and installed a taller, more powerful wind generator that allowed us to take data further into the winter while the sun dipped below the horizon.