Tag: Arctic 2011

Ice Cap Recap

From: Kathryn Hansen, NASA’s Earth Science News Team / Cryosphere Outreach

May 16, 2011

Last month, IceBridge surveyed Sukkertoppen Ice Cap — a mass of ice southwest of the mission’s base in Kangerlussuaq, Greenland. I didn’t know what to expect from an ice cap. Would it resemble the vast, white expanse of the Greenland Ice Sheet next door?

At the surface, Sukkertoppen looked remarkably like an ice sheet. After all, both form from the accumulation of snow compacted over thousands of years. Before long we reached the rugged mountains and blue-green fjord that separates the cap from the main ice sheet, and we turned back for another pass.

On April 8, 2011, IceBridge flew a mission to coastal areas in southwest Greenland. Mountains and an open-water fjord surround one of the mission’s targets, a small ice cap called Sukkertoppen Isflade. Credit: NASA/Michael Studinger

Ice caps are simply small versions of ice sheets, measuring in at a maximum area of 50,000 square kilometers (about 19,000 square miles). Anything larger is considered an ice sheet. They’re also thinner. It’s their small stature that makes ice caps more prone to melt in a warming Arctic.


Charles Webb of NASA’s Goddard Space Flight Center in Greenbelt, Md., explains the importance of monitoring ice caps in the Canadian Arctic. Credit: NASA/Jefferson Beck

South of Sukkertoppen lies the Canadian Arctic – home to the largest amount of ice outside of Greenland and Antarctica and contributing significantly to sea level rise.

IceBridge is adding to the long-term record of changes to the ice caps. On May 5, IceBridge surveyed the Devon Ice Cap – among the Canadian Arctic’s top ten largest caps. Then on May 10, the P-3 surveyed several glaciers and small ice caps on Ellesmere Island, Axel Heiberg Island and Meighen Island, including the Prince of Whales Ice Field and the Agassiz Ice Cap.

Finally on May 12, IceBridge surveyed the Barnes Ice Cap. Barnes is a curiosity because it is considered a significant remnant of the vast Laurentide Ice Sheet the covered most of Northeast America and Canada during the last glacial. NASA previously used the ATM laser altimeter to map the ice cap in 1995, 2000 and 2005, showing a slight acceleration in thinning of the ice cap.

“It’s our hope that by combining these data sets we’ll have a long term time series about whats happening there so we can better understand the dynamic of the ice caps as well as use them as early warning indicators of what is happening in our climate,” said Charles Webb of NASA’s Goddard Space Flight Center in Greenbelt, Md.

On May 12, IceBridge surveyed Barnes Ice Cap on Baffin Island. In addition to mapping its surface elevation, instruments also measured the bedrock topography, which will allow scientists to better model ice dynamics and estimate when the Barnes Ice Cap will be completely melted. Credit: NASA/Michael Studinger

Measuring Gravity From a Moving Aircraft

From: Joël Dubé, Engineer/Geophysicist at Sander Geophysics, OIB P-3 Gravity Team

One of the instruments used in Operation IceBridge (OIB) is an airborne gravimeter operated through a collaboration between Lamont Doherty Earth Observatory of Columbia University and Sander Geophysics. Some people from other instrument teams call it a gravity meter, gravity, gravitometer, gravy meter, gravel meter, gravitron, or blue couch-like instrument. As operators of the gravimeter, we are referred to as graviteers, gravi-geeks or gravi-gods. This tells a lot about how mysterious and unknown this technology appears.

Let me summarize the basics of airborne gravity data acquisition for you.

But first, why is gravity data being acquired as part of OIB?

The earth’s gravity field is varying in space according to variations in topography and density distribution under the earth’s surface. Essentially, the greatest density contrast is between air (0.001 g/cc), water and ice (1.00 and 0.92 g/cc, respectively) and rocks (2.67 g/cc in average). Therefore, gravity data can be used for modelling the interface between these three elements. The ATM system (laser scanner) can locate the interface between air and whatever is underneath it with great accuracy. The MCoRDS system (ice penetrating radar) is successful at locating the interface underneath the ice. However, no radar system can “see” through water from the air. Hence, gravity data can help determine bathymetry beneath floating ice, either off shore or on shore (sub-glacial lakes). This in turn enables the creation of water circulation models and helps to predict melting of the ice from underneath. Also, airborne gravity data can contribute to increasing the accuracy and resolution of the Earth Gravitational Model (EGM), which is determined only with low resolution in remote locations such as the poles, being built mainly from data acquired with satellites.

Most people don’t know that it is possible to acquire accurate gravity data from a moving platform such as an aircraft. Due to the vibrations and accelerations experienced by the aircraft, it is definitively a challenge! There are four key elements that make this possible.

1- You must have very accurate acceleration sensors, called accelerometers.

2- You must keep these accelerometers as stable as possible, and oriented in a fixed direction. This is a job for gyroscopes coupled with a system of motors that keeps the accelerometers fixed in an inertial reference frame, independently of the attitude of the aircraft. This is why the system we use is called AIRGrav, which stands for Airborne Inertially Referenced Gravimeter. Damping is also necessary to reduce transmission of aircraft vibrations to the sensors. The internal temperature of the gravimeter also has to be kept very stable.

This is all good. However, the accelerations we are measuring this way are not only due to the earth’s gravity pull, but also (and mostly) due to the aircraft motion. And to correct for that:

3- You need very accurate GPS data, so that you can model the aircraft motion with great precision.

Despite these best efforts, noise remains, mostly from GPS inaccuracies and aircraft vibrations that can’t be detected by GPS, so:

4- You have to apply a low pass filter to the data, since the noise amplitude is greatest at high frequency.

The AIRGrav system on-board the P-3 aircraft. Gravimeter (right), rack equipped with computers controlling the gravimeter and GPS receivers (center) and operator (left). Credit: Joël Dubé

Furthermore, a number of corrections have to be applied to the data before they can serve the scientific community. The corrections aim at removing vertical accelerations that have nothing to do with the density distribution at the earth’s sub-surface.

The Latitude correction removes the gravity component that is only dependent on latitude. That is the gravity value that would be observed if the earth was treated as a perfect, homogeneous, rotating ellipsoid. This value is also called the normal gravity. Since the earth is flatter at the poles, being at high latitude means you are closer to the earth’s mass center, hence the stronger gravity. Also, because of the earth’s rotation and the shorter distance to the spinning axis, a point close to the pole moves slower and this will add to gravity as well (less centrifugal force acting against earth’s pull).

Anything traveling in the same direction as the earth’s rotation (eastward), will experience a stronger centrifugal force thus a weaker gravity, and the other way around in the other direction. Traveling over a curved surface also reduces gravity no matter which direction is flown, similar to feeling lighter on a roller coaster as you come over the top of a hill. This is known as the Eötvös effect and is taken care of by the Eötvös correction. This correction is particularly important for measurements taken from an aircraft moving at 250-300 knots.

The Free Air correction simply accounts for the elevation at which a measurement is taken. The further you are from the earth’s center, the weaker the gravity.

To give you an idea of how small the gravity signal that we are interested in is with respect to other vertical accelerations that have to be removed, let’s look at the following profiles made from a real data set. All numbers are in mGals (1 m/s2 = 100,000 mGals), except for the terrain and flying height which are in meters.

A visual summary of gravity corrections. Credit: Stefan Elieff

“Raw Gravity” in this diagram means that GPS accelerations (aircraft motions) have been removed from inertial accelerations. Notice the relative scales of the profiles, starting at 200,000 mGals, down to 20,000 mGals when aircraft motions are accounted for, down to 200 mGals after removing most of the high frequency noise, and ending at 50 mGals for Free Air corrected gravity. Free Air gravity is influenced by the air/water/ice/rock interfaces described earlier, and since OIB uses the gravity data to find the rock interface (the unknown), Free Air gravity is the final product. As a side note, for other types of gravity surveys, we usually want to correct for the terrain effect (the air/water/rock interfaces are known in these cases), so that we are left with the gravity influenced only by the variations of density within the rocks. This is called Bouguer gravity and is also shown in the figure.

Notice the inverse correspondence between flying height (last profile, in blue) and the profiles before the free air correction (going higher, further from the earth, decreases gravity), and the correspondence between terrain (last profile, in black) and the free air corrected data.

Now, let’s look at some data acquired during the current 2011 mission in western Greenland.

Ice elevation (left), rock elevation (middle) and Free Air gravity data (right). Greenland 2011 flight lines shown in black. Gravity data is preliminary and is not yet available for scientific analysis.

The left panel shows the elevation of the rocks, or of the ice where ice is present. It is as if the water has been drained from the ocean. The middle panel shows only the bedrock elevation, both ice and water being removed. The data is from ETOPO1, a global relief model covering the entire earth. The right panel shows the Free Air gravity acquired in the last few weeks. Most channels, called fjords, are well mapped by the gravity data. It is interesting to see that the gravity data infers the presence of a sub-glacial channel (shown by the red arrow) where no channel is mapped (yet?) on the bedrock map. The most likely reason for this is that this particular region has not been covered by previous ice radar surveys (there are huge portions of the Greenland ice sheet that remain unexplored). Note that the MCoRDS ice radar data acquired as part of the current campaign will improve the resolution in this area and will enable for a better comparison of both data sets in the future.

Battling the Arctic Chill

From: Kathryn Hansen, NASA’s Earth Science News Team/Cryosphere Outreach

April 6, 2011

Kangerlussuaq, Greenland — It may seem obvious, but the Arctic is cold. I was surprised to arrive in Kangerlussuaq, Greenland, to see the hills and streets covered with snow and temperatures that make you second-guess the wisdom of leaving any skin exposed.

In 2010, the Kangerlussuaq leg of Operation IceBridge began about a month later, in May. What a difference a month makes. The hills were snow-free, flowers beginning to bloom, days were long, and the river rushed to break up the last chunks of winter ice. On down days, crew and science teams hiked, biked and went fossil hunting. Now we mostly stick to the warm indoors. Most of us, however, are willing to brave the cold and dwindling hours of darkness to catch a spectacular show of the northern lights.


This time lapse of the northern lights consists of 30-second exposures spanning just over an hour. We took turns behind the camera, running inside every 15 minutes to quickly warm up. Credit: NASA/Jefferson Beck

It turns out that the aircraft also battles the cold. On April 5, we planned to fly the mission’s first science flight from Kangerlussuaq to collect data over Jakobshavn — Greenland’s fastest moving glacier. At 6 a.m. it was just -11 F. The coffee pot onboard froze and fractured.

Shortly after take off, the cold temperatures resulted in a mechanical issue on the aircraft that forced an early return to Kangerlussuaq, Greenland. The P-3’s adept aircrew was quick to diagnose and resolve the issue.

John Doyle, a P-3 flight mechanic, is on the aircraft early and prepared for the cold. Credit: NASA/Kathryn Hansen

On April 6, crew started the day extra early at 5:30 a.m. when the temperature measured in even chillier at -18 F. Additional heating for an extended period prior to flight led to a successful first flight from Kangerlussuaq. And what a spectacular, clear flight.

The DMS, a downward looking camera system, captured this shot of Jakobshavn’s calving front. Credit: NASA/DMS team

Instrument teams onboard the P-3 also battle with the effects of temperature. Scientists with the laser altimeter use hair dryers to warm up the instrument, but too hot is also problematic. Scientists working with the radar instruments prefer the cooler time of year before melt ponds appear on the ice, complicating the way light reflects from the surface.

Having overcome challenges posed by the cold, we’re looking forward to a long series of land ice flights over Greenland. There’s word among the crew that the new coffee pot should arrive in a few weeks, in time for IceBridge’s return to Thule. Thanks to the P-3 crew for what might be the best cup of Joe in Greenland!

In the absence of coffee pot, P-3 crew construct a makeshift filter out of a water bottle. Credit: NASA/Kathryn Hansen

A Five-Hour Survey

From: Kathryn Hansen, NASA Earth Science News Team / Cryosphere Outreach

April 3, 2011



Colors show elevation differences across the airport’s ramp in Kangerlussuaq, Greenland. The map is used to calibrate airborne instruments. Credit: NASA/ATM team

Kangerlussuaq, Greenland — During the last IceBridge campaign, based in Punta Areans, Chile, we described a three-hour ramp survey. Scientists drove a truck with a GPS antenna affixed to the roof to map the precise elevation of the airport’s entire ramp — the pavement next to the runway where the aircraft spends each night. The ramp map helps researchers calibrate science instruments on the aircraft.

Here in Greenland, at Kangerlussuaq International Airport, the same activity on Saturday, March 3, would turn into a five-hour survey.

“This has to be the biggest ramp in the world,” said Kyle Krabill who drove the car, bringing me along as the unsuspecting passenger.

The task started that morning after idling for an hour on the ramp to calibrate the GPS. Then, we rolled off at a whopping 15 miles per hour, windows rolled down and 80’s Danish music blaring. Back … and forth … and back … and forth … we traced around the perimeter of the ramp and then inward, as if we were mowing a lawn of pavement.


A time lapse shows one hour of four-hour-long ramp survey. Video credit: NASA/Jefferson Beck

“See how easy it is to be a scientist?” Krabill joked. But it turns out that driving the car is just the beginning.

Krabill is part of the team that runs the Airborne Topographic Mapper (ATM), an instrument flying with IceBridge. ATM pulses laser light in circular scans on the ground. The pulses reflect back to the aircraft and are converted into elevation maps of the ice surface.

Toward the end of each flight, ATM laser elevation data are also collected during a pass over the ramp. Putting the data all together (including the dizzying ground-based ramp survey), and knowing the precise location of the aircraft (via a technique called “differential GPS”) scientists can decipher and eliminate some of the inherent error that comes with flying a laser scanner, such as errors in range — the physical distance to the ground — and in the team’s knowledge of the way in which the scanner is mounted in the aircraft.

“Differential GPS is fundamental to what we do,” said John Sonntag, ATM senior scientist. “It’s tremendously powerful, taking position error down from about 10 meters to 10 centimeters or better — a huge improvement.”

P-3 Back in Service

April 2, 2011

Kangerlussuaq, Greenland — The P-3 is ready to return to IceBridge just 30 hours after the aircraft’s prop valve failed on Friday, April 1. Here we list highlights from the tremendous effort by aircraft crew who were responsible for the speedy return to flight.

P-3 crewmen John Doyle and Brian Yates work on engine #2. Credit: NASA/Jim Yungel


Friday morning:

1. From Kangerlussuaq, Greenland, get permission to ferry the aircraft to its home in Wallops Island, Va.

2. Line up customs at Dover Air Base

3. File a flight plan

4. Fuel the aircraft

Friday night:

5. Remove the propeller on engine #2

Saturday morning:

6. Replace the P-3 propeller valve

7. On the ramp, let the aircraft’s engine run

8. Functional checkout flight (successful!)

Sunday:

9. Take a much-deserved mandatory hard down day in Wallops Island, Va.

Monday:

10. The P-3 is scheduled to depart Wallops at 7 a.m. EDT and arrive in Kangerlussuaq at 4:30 p.m. local time, ready for a possible flight on Tuesday!

Engine run up under way on the ramp at Wallops. Credit: NASA/Jim Yungel

LVIS is in the Building

From: Kristyn Ecochard, NASA’s Langley Research Center

Crewmembers are busy getting the B-200 King Air at NASA’s Langley Research Center in Hampton, Va. ready for its first flight with Operation IceBridge.

The King Air will be carrying the Land Vegetation and Ice Sensor (LVIS) onboard for several weeks of science flights over the Arctic. LVIS is an instrument from NASA’s Goddard Space Flight Center in Greenbelt, Md.

Engineers are uploading the instrument and other science equipment in preparation for a scheduled departure date of April 13.

IceBridge teams are already in Greenland conducting science flights onboard the P-3B based out of NASA’s Wallops Flight Facility in Wallops Island, Va.

The B-200 King Air at NASA’s Langley Research Center is a small plane that can get up to 35,000 feet. Credit:NASA/Sean Smith


The King Air will only carry one instrument on its science flights over the Arctic: the Land Vegetation and Ice Sensor (LVIS) operated by NASA Goddard Space Flight Center’s David Rabine and Shane Wake. Credit:NASA/Sean Smith


NASA Goddard Space Flight Center’s Land Vegetation and Ice Sensor (LVIS) will map large areas of sea ice and glacier zones. Credit: NASA/Sean Smith

Weathering the Storm

Spring officially arrived on Sunday, but for IceBridge scientists in Thule, Greenland, spring was nowhere to be seen. Teams awoke Monday to a storm that continued through the day and by 5 p.m. local time, Thule Air Base had declared “Delta” status, prohibiting on-base travel and confining personnel to the buildings.

The storm on Monday in Thule intensified to “Delta” status. IceBridge scientists waited out the storm indoors. Credit: NASA/Jim Yungel

While snow blows outside, IceBridge project scientist Michael Studinger briefs the teams at the nightly meeting. A science flight the following morning would require clear skies. Credit: NASA/Jim Yungel

With no other options for food, some scientists turned to MREs (Meal, Ready-to-Eat), including this southwest style beef and beans with Mexican style rice, picante sauce, and chocolate disk cookie dessert. Credit: NASA/Jim Yungel

The ground-based GPS antennas did not fair as well in the storm, although both stations have since been reestablished and ready for a science flight. Credit: NASA/Kyle Krabill

By Tuesday morning the storm had passed and crews were quick to plow the runway. Credit: NASA/Jim Yungel

With a clear runway, the P-3 was rolled out for a long-awaited, high-priority sea ice flight to Fairbanks, Alaska. Credit: NASA/Jim Yungel

An Uncommon Routine

From: Michael Studinger, IceBridge project scientist, Goddard Earth Sciences and Technology Center at the University of Maryland, Baltimore County

Thule Air Base, Greenland — The IceBridge team arrived in Thule last week and the campaign is off to a good start. We flew four out of five days last week and accomplished three sea ice missions including an underflight of the European Space Agency’s CryoSat-2 satellite over the Arctic Ocean. After a week here in Thule, we are settled in and our operations have become routine.

Operation IceBridge accomplished three science missions during the first week, including an underflight of ESA’s CryoSat-2 over the Arctic Ocean just 120 miles from the North Pole. Credit: NASA

A typical IceBridge day in Thule Greenland starts at 5 a.m. when my alarm clock goes off. I start downloading satellite images to get an idea which missions may be possible to fly before I go to breakfast at 5:45 a.m. At 6:15 a.m., the pilot in command, mission manager, John Sonntag and myself meet at Base Ops to get a weather brief for the day.

The three meteorologists at Thule Air Base have known us for years and do an excellent job in providing us with a very detailed and specialized weather brief that we require for decision making. The demands for research flights are different from everyday air travel, and the polar environment poses great challenges in terms forecasting the weather. There is not a single weather station within hundreds of miles of our survey area that we could use to get a weather observation or that would provide observational data as input into a forecast model. Instead, we depend on satellite images that are several hours old. Visible images are dark for any area west of us. It requires experience and skill to interpret the forecast products for our purpose.

A few days ago, a model transect along our flight path showed dense cloud cover along the entire mission profile at 500 meters flight elevation calling for a no-fly day. We spent time with the meteorologists to understand the weather situation and decided to fly, despite the grim looking forecast. It was the right decision. The cloud layer depicted by the forecast model turned out to be a thin layer of haze that did not pose any difficulties for our laser and digital imagery sensors.

The weather forecast is shown along a survey line for a P-3 science mission. The forecast predicts dense cloud cover at the flight elevation (500 m), but after carefully studying the weather situation, we decided to fly. Credit: NASA

Between 6:30-6:45 a.m. we make a go/no-go decision. If we fly, the aircraft gets pushed out of the hangar and the fuel truck arrives. We need to collect one hour of static GPS data on the ground to calculate high-precision trajectory data from our flights. At 7:30 a.m. the door of the aircraft closes and we taxi to the runway to be ready for an 8 a.m. takeoff as soon as the tower opens.

We typically transit to the survey area north of Thule and then descend to 1,500 feet were we start collecting data. It’s still early in the season, which means missions west of Thule are flown in near-constant twilight, with the sun following us as we go west. When we turn around the western end of the line and fly back east, it immediately start getting lighter with every minute of the flight.

During the flight the operators monitor their instruments and make sure we collect high-quality data. Occasionally, adjustments need to be made to ensure the instruments keep working.

In-flight adjustments are often necessary to keep the instruments working and collecting high-quality data. Adjustments often require work below the deck to access the instrument sensors in the belly of the P-3. Credit: NASA/Michael Studinger

At 3:45 p.m. we typically land to leave enough time for a 1-hour post-calibration with the aircraft outside. By 5 p.m. the aircraft is rolled back inside the hanger and doors close for the night.

John Sonntag and myself quickly stop by Base Ops for another weather brief to see what’s in the mix for the next day. At 5:30 p.m. we have a science meeting where we discuss plans for the next day and talk about issues that are worth sharing with others. After the meeting, most people go straight to dinner followed by a late evening spent backing up data and processing data.

At 5 a.m. the next morning we start again.

A lateral moraine can be seen at the margin of the Greenland Ice Sheet near Thule Air Base. Credit: NASA/Michael Studinger

View From the Hut

We previously wrote about the Met Huts in Kangerlussuaq and Thule, Greenland –- the ground-based GPS stations that help scientists to ensure that GPS information collected on the aircraft is as accurate as possible. Kyle Krabill is back in Thule for the Arctic 2011 campaign making sure hut operations run smoothly.

From: Kyle Krabill, ATM Instrument Team Engineer, NASA’s Wallops Flight Facility

“Took a couple pictures this morning [March 17] from my view here at the hut. Sunrise is getting earlier by 13 minutes or so each day. The guys are flying another mission again today. Had a little warm front come through last night and its up to a balmy -17 (if you’re out of the wind)”

The P-3 passes over the Met Hut on March 17, 2011. Credit: Kyle Krabill

The sun rises in Thule, Greenland, as seen from the Met Hut on March 17, 2011. Credit: Kyle Krabill

Teacher, Student Blog From the Arctic

A teacher and student from the U.S. Naval Academy in Annapolis, Md., joined IceBridge in the field for the Arctic 2011 campaign. Follow their Arctic adventures here.

LCDR John Woods is a Meteorology and Oceanography Officer (METOC) currently teaching in the Oceanography Department at the United States Naval Academy (USNA). He is part of the Sea Ice Thickness Observation team currently participating in NASA’s Operation Ice Bridge 2011.

Eric Brugler is First Class Midshipmen who is an honors Oceanography major at the United States Naval Academy. He is interested in the polar regions of Earth because he believes they play a very important role to the Earth’s climate system.