Posts Tagged ‘Radar’

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Radar survey of Röhss Glacier

January 14, 2010

Martin Truffer, of the University of Alaska, tows a radar sled across Rohss Glacier.

Ted writes:

On January 11, two of the glaciology team aboard the N.B.Palmer, Erin Pettit and Martin Truffer of University of Alaska, flew to nearby Röhss Glacier to conduct a radar survey and test the science equipment. Although not part of the original LARISSA mission, the Röhss Glacier is similar to the glaciers of the Larsen B embayment in that it is rapidly retreating and thinning in the aftermath of ice shelf disintegration, in this case, the disintegration of the Prince Gustav Ice Shelf in January 1995. The Röhss has retreated nearly 25 kilometers (16 miles) in that time.

The survey tested the deep radar system that we plan to use on the Larsen B glaciers, which measures ice thickness. We also measured the glacier flow rate at the site using precision GPS systems. Early results show that the glacier is roughly just 200 meters (700 feet) thick at this point, and flowing at about 200 meters (700 feet) per year.

Erin writes:

Ted has been studying this glacier’s retreat through satellite imagery, so he was pretty happy to have Martin and I get some ground data to supplement his satellite work. It was, of course, a glorious flight over with Chris. We stopped on a bedrock knob next to the glacier to set up a quick GPS base station. It’s all volcanic rock over there, with lots of crumbly pumice.

Ted had given us approximate coordinates based on his satellite images for landing on the glacier. The entire lower part of the glacier is broken up with crevasses due to its fast retreat, so the point Ted gave us was in the middle of a crevasse field. But as it was the most interesting part of the glacier for the data we wanted, we chose a broad, flat icy area between two large rifts. The flat area was probably 200 or 300 meters (700 to 1000 feet) long and 30 meters (100 feet) wide. It was snow-free, with dirty ice showing through, so we new it was safe to land and work.

We put a GPS on the glacier to measure its motion. Martin’s processing of those data this morning show that it’s moving about 60 centimeters (24 inches) per day. We also strung out our radar system (two 20-meter antennas, which spread out quite a ways on our little ice ledge). We profiled as much terrain with the radar system as we could safely between crevasses,  about 200 meters. We had fun navigating around snow patches, which can hide crevasses. We also jumped over a few tiny crevasses in the ice, where we could see what was solid and what was not.

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The Storm

December 21, 2009

The LARISSA IPR Team is now flying north over the Southern Ocean, towards the Straits of Magellan, and home. This is the second part of Ted’s update:

Ted writes:

It began with a haziness, an odd light, at midnight on the fourth day. There’s an old saying about the color of the sky at sunrise and sunset. But what if sunset happens at midnight, and it’s also sunrise, at the same time? An ice fog blew across the camp, flocking everything with feathery or bristly crystals. Rothera told us by radiophone to prepare for the worst.

To our surprise, the next morning was still fair enough to try to finish the last of the survey. Rob and I suited up, and managed to drive about 20 km of data before our batteries ran out. We turned back just in time. By 2 p.m. the wind had risen to 30 knots, and we were shouting over it to tie things down, close things tight, get supplies and gear where we needed it for a long wait. We dove into the tents at 3 p.m., and then the weather really broke. By 4 p.m. the wind was howling at 45 knots, snow was screaming past the plastic windows of the tents, and huge plumes of drift streamed away from each tent, as if each were the head of a comet streaking across the sky.

That night was one of the most thrilling of our lives: the sounds, the power of the storm, feeling the might of it through the thin fabric wall of the tent. There was an entire spectrum of sounds. The lower level of blowing snow was a hissing, sandy undertone against the tent; then the tympany of the tent fabric, like a crescendo in a symphony that would not end. But there was more: there were times when the wind seemed to thunder into the very ground beneath us, as though God was hammering away at the camp with stupendous boxing gloves. There were times when the hissing would be interrupted by a clattering, as nearby dunes of snow blew to pieces and scattered agains the tent walls. At one point, there was a sound like rainfall against the tent: a truly terrifying thought for an Antarctic field party. We surrounded ourselves with books, snacks, and a death-defying humor, radioing each other the tents to ‘check in’: ‘Hey, you ok? We were thinking of tunneling over for dinner.’

If you’re wondering, we peed in bottles. As for anything else, well, we waited.

Rob arrives for breakfast

On the following morning, Rob and I decided to go over to Erin’s tent, despite the storm, and have a ‘proper breakfast, dammit’. We suited up, tightly, tied the boots on, and pushed on the fabric tunnel door of the tent. It was buried. To get out, we had to kick our way out, or shove against it like a football player.  The wind (we were later told) had reached a maximum of about 60 knots.

Having kicked a path clear in the door, I crawled out through the short tunnel doorway and looked up. Instantly I was gagged by snow, blinded as well, and staggered by the force of the wind. Erin’s tent was a hazy outline flickering between gusts, barely visible but just 30 feet away. The camp flags were flapping at an impossible staccato pace no rock star drummer could ever match.

I stood (I was not going to crawl), took a step, and immediately stumbled.  Crawling might not be such a bad idea. There were new ridges and ditches everywhere, the camp landscaping was completely redone by the blowing snow. Each tent had its own crater forming around it, and the snow ridges on either side were 2 feet tall. Boxes had disappeared. The main sled had disappeared. There were flagpoles that had snapped in the wind.  There was no horizon, no contrast, just vague shapes, like a tent or a box, emerging from a grey-white shrieking haziness.

Rob and I staggered over to Erin’s door. It too was buried, but the shovels were still there by the door where we had staged them prior to hunkering down. For the next 12 hours we sat in the tent, cheery, not exactly warm but at least with food and a stove, and computers to look at. Slowly, in the storm, the data was processed, and a report was written on the region.  We found the site we needed. And in a gap in the wind of 8 hours the following day, we were pulled out (at the last possible hour to make our flight north).

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Mapping beneath the ice

December 21, 2009

The team has returned from the field, and sends this update (part one of two)

Ted writes:

We arrived at Rothera, a British base on an island just off  the southeast side of the Antarctic Peninsula, on Sunday, December 6. The camp is set in the most spectacular polar landscape you can imagine: mountains drenched in frosting ice. Some of it is windswept and blue, some of it shatters under the stress of flow over bedrock and scattered sea ice adrift in the wind. Almost surrealistic is the natural sculpture garden of icebergs, set out by some immortal art director in the bay just in front of the main dining and living building (New Bransfield House). It’s the kind of landscape reveals the hidden power of the forces at work in Antarctica: ice, ocean, weather, wind. It is a landscape of natural power. Orcas play in the open water between the bergs.

Rothera Base is built on either side of its two most valuable assets, a flat 3000-foot, perfectly smooth gravel airstrip, and an excellent deep-water wharf. The conjunction of these two things means that it’s a place where wheeled aircraft from the north, ships from anywhere, and ski aircraft of the deep icefield activities can mingle. Rothera stands at a rare logistical trifecta on the Antarctic coast. The base houses about 100 people, and has room for 150 (astonishing to find a base in Antarctica with room to spare). To a person, we met energetic cheerful people, starting with the base commander, John Withers, the science liason Tamsin Gray, the hanger staff (Clem, a veteran of four winters and countless summers), and the ‘Saints’, the team of staff from the island of St. Helena who run the kitchen, maintenance, cleaning, laundry, etc. We really enjoyed the people and personality of Rothera. It’s a gem, it’s successful, and it’s efficient.

By late that afternoon, we had our bunks set up, a large office (which we packed nearly full with our gear), and we were well on our way to finding everything that had been shipped down for us earlier: a snowmobile, sleds, generators, tents, food; all in all about 4000 pounds of gear to make our own outpost on the ice. We spent the next day (a spectacular day of sunshine) testing our radar gear at a nearby snowfield, ably assisted by Adam.  On Tuesday morning we were told the weather would be good enough for a put-in of our camp on the ridge crest of the Antarctic Peninsula.

The goal for the IPR study (Ice Penetrating Radar) is to find a good site for drilling the LARISSA ice core. With the ice core, we are hoping to retrieve a record of climate for the past several thousand years–the older the better. So the key is to find a spot that has smooth ice layers, and lots of them, from top to bottom. Earlier, the LARISSA team had pored over what data was available from aircraft and satellite, and selected a search area. It was our job to fill in the gaps in the search region with a ground survey, using ice radars, GPS, and all the previous data together. Basically, we had to put an X on the map, the best X we could find.  We had about 5 days.

The put-in by Twin Otter could not have gone better. The weather was clear, warm (about -8°C. That’s warm, isn’t it?), and best of all light winds. By the time I got there on the second flight, Erin and Rob already had the tents set up and the basic layout of the camp done. We looked it over, baking in the intense sunshine, the camp all neatly laid out and clean.  A smooth white plain stretched to the horizon, but in the distance there were mountain pinnacles and ridges, black like jet glass shards rising from the ice. I dared to be optimistic.

The next day proved to be more of a challenge. The wind picked up to 25 knots, and snow began to blow across the surface. We still managed to get the science gear mounted on the sleds, and by the end of the day we were comfortable with our plans to resurvey the airborne data and drive a grid pattern over the 8 by 8 km region we were mapping. In the next three days, we packed 70 km of snowmobile driving into that 8 by 8 box. Things could not be going better.

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Update from the ice field

December 14, 2009

Terry Haran is still in Boulder, Colorado. He’ll be departing on Christmas Eve for Punta Arenas (shortly after Ted returns home for a short holiday visit) to participate in the second leg of the trip.

Terry writes:
The team is currently near the summit divide of the Bruce Plateau, conducting an Ice Penetrating  Radar (IPR) survey. The goal of the survey is to help determine the optimum location for retrieving an ice core. Ellen Moseley-Thompson and a team from the Byrd Polar Research Center (BPRC) plan to drill the core in January and February 2011. Their team will deploy to the to the same location as soon as the IPR team is finished.

The purpose of the ice core is to characterize the paleoclimatology of the LARISSA study area going back in time as far as possible, hopefully as much as 10,000 years or so. The ideal location would have a depth to bedrock of about 500 meters (about the maximum depth that the BPRC team will be able to drill in the time alloted to them), and would have a relatively smooth bedrock surface.

Ted’s team also hopes the IPR survey can characterize the inter-annual layering found in the upper 100 to 200 meters of the much younger snow cover known as “firn” that is in the process of compacting to eventually become ice. The ideal layering found at the ice core site would be horizontal and uniform with little evidence of firn motion downhill from the summit ridge.

Over the weekend, we got a few updates from the field. I spoke to Ted on the phone, and he said they had surveyed about 60 kilometers with the 5 MHz (deep) radar and were getting good data with it. They think they’ve accomplished all they need to with this radar.

In the next few days before the team return to Rothera Station, they were hoping to resurvey some lines with the 25 MHz (medium depth) radar and to obtain some higher precision differential GPS data for some survey markers than they had geolocated with their hand-held GPS. However, a powerful storm was on its way, so they decided to spend Sunday preparing for the storm and staying in their tents analyzing the 5 MHz data they have collected.

The latest update we received, from the LARISSA operations team, informed us that the team is ready for pickup. However, because of bad weather that’s expected to stick around for the next couple days, they might not be able to get a plane in for a few more days.

The MODIS images below show the location of the team on the Antarctic Peninsula

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Rothera Station, Antarctica

December 8, 2009

Rob writes:

We have arrived at Rothera Station! Erin, Ted and I had a great flight south from Punta Arenas, Chile to Rothera Station, arriving Sunday afternoon. The team jumped right in to organizing our equipment for the flight to the survey site. Monday brought more cargo work and a shakedown cruise of the radar systems. It was a long day, but everyone had a great time.

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