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Antarctic Fieldwork with a Surface-Based Radar.

3 June 2022

Improving our understanding of radar penetration is part of a recently-funded NERC project named DEFIANT. Robbie Mallett's role was to lead the radar-physics component of the first DEFIANT field campaign in the Weddell Sea of Antarctica.

Jeremy Wilkinson (BAS) and I digging a snow pit. A tabular iceberg can be seen on the left-horizon. Photo by Timo Hecken, German Heliservice.

By comparison to measuring its area coverage, accurately measuring the thickness of floating sea ice with satellites is extremely hard. Measurements are traditionally performed by bouncing radar waves off the surface of the sea ice and timing their return; however this approach is plagued by uncertainties concerning the ability of the radar waves to penetrate the overlying snow.

The floe that supported us on the final day. By this point we were drifting freely and the floe was rotating and moving relative to its neighbours. Photo Timo Hecken, German Heliservice.

Captions: The floe that supported us on the final day. By this point we were drifting freely and the floe was rotating and moving relative to its neighbours. Photo Timo Hecken, German Heliservice.

Improving our understanding of radar penetration is part of a recently-funded NERC project named DEFIANT. I was lucky to lead the radar-physics component of the first DEFIANT field campaign in the Weddell Sea of Antarctica. We measured the radar reflectivity of snow covered sea ice as a function of depth. That is to say, we fired radar waves at the snow and measured where they were reflected from. Our field campaign took place over two months in March and April, where we worked from the German research vessel Polarstern.

We generally visited the sea ice floes by helicopter. This involved taking apart the radar each day and strapping it to its sled for transport, then reassembling it at the field site.

The radar instrument in situ.

Caption: The radar instrument in situ.

This was a pretty stressful experience, as the radar is extremely fragile. The sled and radar fit in the back of the helicopter with around 2cm to spare! Selecting a floe was tricky; as soon as we landed we would drill down into the floe to mesaure its thickness, in part to check it was safe to park the helicopter there. Floes were often much thicker or thinner than we guessed from the air.

We managed to dig seventeen snow pits on five floes, and scanned each pit with the radar at two different frequencies. In our snow pits we measured snow temperature, hardness and density profiles. We also mapped the stratigraphy (layering structure), took photographs and made other more general observations of the snow condition. The radar team at CPOM UCL will now work on the radar and snow pit data over the next few months.

The radar instrument stands next to us while we dig a snowpit over rough sea ice. Photo Timo Hecken, German Heliservice.

Caption: The radar instrument stands next to us while we dig a snowpit over rough sea ice. Photo Timo Hecken, German Heliservice.

I’m really grateful for the support of Jeremy Wilkinson and Povl Abrahamsen (both from the British Antarctic Survey) while in the field. They’re both hugely experienced and were incredibly supportive of me while we were aboard Polarstern. I’m also grateful to my supervisor Julienne Stroeve for backing me to go – the radar itself is both expensive and fragile, so entrusting it to a PhD student was a bit of a leap of faith. I’ll also be on DEFIANT’s next bit of fieldwork in 2023: overwintering on the Antarctic peninsula with the same instrument.

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