Editor’s Note: Welcome to ANITA, the Antarctic Impulsive Transient Antenna! From October to December, Katie Mulrey is traveling with the ANITA collaboration to Antarctica to build and launch ANITA III, a scientific balloon that uses the entire continent of Antarctica for neutrino and cosmic ray detection. This is the third installment in a series, “Neutrinos on Ice,” documenting that effort.
It has officially been two weeks since we've seen the sun set! It's been surprisingly easy to get into a routine here. We work seven days a week to make sure ANITA will be ready on time, so each day feels the same.
Every morning we wake up and catch a bus to the CSBF Long Duration Balloon (LDB) facility. It is located in the shadow of Mount Erebus, the most southern active volcano on Earth. It's always smoking to remind us that it is alive. We've found out that it is much colder out there than it is in town. Thank goodness for all of our cold weather gear! McMurdo Station is located on land, but the LDB is built on the Ross Ice Shelf. On the ride in we drive over the boundary between the two.
When the ice moves against the land it creates awesome pressure ridges that develop over time and look like huge frozen waves. This is where seals like to pup, since they can climb out of the water onto the ice through cracks near the ridges. We happened to see a new born seal pup in the area last week!
We are stationed in an airplane hanger. It was empty when we showed up, but day after day it filled up with more equipment as shipping containers arrived.
Now it's time to start building! This is one of the most exciting phases of the experiment. The gondola (the structural frame of the payload) starts out as thousands of pieces of carbon fiber tubing and metal connectors. It is built from the top down. The communication equipment and solar panels are at the very top. The GPS and communication antennas need to be on the top of the payload so they have direct access to satellites. Next come the antennas. The antennas are organized radially into sixteen “phi sectors” and are tilted ten degrees down towards the continent. This way we can see over the ice in all directions
ANITA consists of 48 broadband antennas (180-1200 MHz) and one low frequency antenna (30-80 MHz). The broadband antennas each have two feeds, one horizontal and one vertical. The vertical polarization is great for detecting neutrinos, since the radio signal propagating through the Antarctic ice has to be vertically polarized to escape without totally internally reflecting. Cosmic ray radio emission is primarily caused by charged particles in the air shower moving horizontally in the Earth's magnetic field, so the horizontal polarization is great for detecting them. The signals coming from all the antennas are cabled to the ANITA “instrument box.”
The signals we see are very faint. If someone on the ice happens to start a car engine, the signal can reach the payload and look very similar to a neutrino signal—so a lot happens between the time the signal reaches the antenna and the time the data is recorded in the instrument box. The RF (radio frequency) signal first goes through an amplifier, then through a long cable, through filters, splitters, more amplifiers, more cables, and then into our triggering and digitizing system. All these components have differing characteristics (times 97 channels!) and need to be carefully calibrated before we can say what our data really means. We do that by sending known pulses into the system and recording what comes out the other side. Our data analysis depends on the exact timing and amplitude of the signals, so calibration is critical.
McMurdo Station is a great place for scientific collaboration. On Sunday evenings we gather in the galley for a science talk from one of the local groups. On weekdays, we play shuffleboard with other scientific teams and jam on guitar with the CSBF crew. There are also lots of great hikes around town. The hike up Observation Hill yields a great view of McMurdo. We have also walked to Scott's Hut, which has been perfectly preserved since the early 1900s. Between full days of science and evenings of once-in-a-lifetime recreation opportunities, there is very little down time here.