The project is several weeks in, and with each new line of data we celebrate the collection and then dig into it to see what we can learn. The map is growing, filling in with the 20 km flights designed to provide a framework for the 10 km flights that would fill in the gaps during our next field season. However, already in some instances the team has tightened their grid lines to 10 kms, taking advantage of opportunities in the weather or the inability to collect a line over another part of the shelf.
(Above is a video of the retraction of the IcePod arm as the plane flies over the Ross Sea Polynya (open water set in the middle of the sea ice). During data collection the pod is lowered and then retracted upon completion. Video by Dave Porter.)
The latest team celebration is around the magnetometer data. Magnetics is used to understand the make up of Earth’s crust. The end goal is to calculate the anomaly or unique magnetic signal from the geology in an area after separating out all the other magnetic ‘interference’ to better understand the formation of this area of Antarctica. The Earth’s magnetic signature varies by location so a base station is set up in order to collect a background magnetic level for the area. During data collection the base station will be used to determine anticipated magnetic levels for the region.
In data processing the local signal is corrected for and small spikes from the aircraft that the instrument is mounted to will be removed. This means that each magnetic survey includes a magnetic compensation flight at high elevation so that the magnetic signature of the plane can be identified. A model is then developed to separate the signal of the plane from that of the geology. The magnetic compensation flight includes flying in all four cardinal directions — check the annotated flight track image above to see a recording of these flight lines.
The compensation flight also includes 3 repeat pitch-roll-yaw moves. Pitch includes tipping the wings side to side, roll is moving the nose and tail down and then up and yaw is a rotating or twisting of the plane left and then right. Thanks to New York Air National Guard loadmaster Nick O’Neil we have a video of the pitch and roll pieces of this compensation flight. Note the video is sped up to show 2 minutes of filming in 17 seconds so hold onto your seats! Be sure to note how the vapor contrail of the plane tracks the serpentine movement of the flight pattern during the rolls!
For the magnetics the flight line selected was one that has been flown previously by the NASA IceBridge program. Duplicating flights between different projects provides an opportunity to test and validate equipment. From the onset collecting magnetics data from the LC130 with the IcePod system was considered challenging. The compact nature of the instruments and all the metal surrounding them made this a real test, however, the resulting first unprocessed flight line (below) shows that the shape of the two lines agree! The alignment will only improve with processing against the base station. This is a significant achievement given the very compact environment of the instruments in IcePod – cause for celebration!
The magnetic image shows the signature of this area of Antarctic geology in clear detail. Flying away from McMurdo the Transantarctic Mountains are on the left side of the dataset. The flight moves towards the highly magnetized volcanic environment of Marie Byrd Land in West Antarctica on the far right. Note the elevated magnetics on the right form the volcanic rock. A magnetic high is also visible in the center, yet on the left side the Transantarctic Mountains show no sign of high magnetism. This is not surprising as this mountain range that stretches mainly north to south across Antarctica, was formed from uplift beginning about 65 million years ago, and is composed of sedimentary layers of rock overlying granites and gneisses.
Magnetics has evolved quite a bit over the years of geophysical sampling. Lamont scientist Robin Bell recalls when in the 1990s when she worked on a project mapping a active subglacial volcanism in West Antarctica that the magnetometer was towed on a winch ~100 meters behind the aircraft. If the wiring got caught up in the tail section it was cut lose and the instrument was lost. More recent work has located the instrument in the tail of the plane (as in the P3 bombers of World War II) and on the tips of the wings of the plane as was the case during the 2008 AGAP work in East Antarctica mapping the subglacial Gamburtsev Mountains. The IcePod model of placing the magnetics so close to the radar has not been done before.
Check out the newest lines on the GIS map and stop back for more.
For more about this NSF- and Moore Foundation-funded project, check our project website: ROSSETTA.
Margie Turrin is blogging for the IcePod team while they are in the field.