Posts Tagged ‘GPS’

Greenland Surface Melt Study 2013: Gearing Up for Greenland: Part 2

November 1st, 2013 by Colleen Brooks

In early September, I drove down to Wallops Flight Facility to set up our GPS base station in preparation for the test flight. The test flight is to verify that everything is working as expected, and to do some calibration, since the C-130 is a new platform for the Land, Vegetation, and Ice Sensor (LVIS). LVIS gathers data by sending out short laser beam pulses that bounce off the ground and give us the elevation of the terrain. Calibration ensures that we can pinpoint to within an inch where the laser hits the ground. We need to know exactly where the instrument is, and what it is seeing on the ground.

We use GPS receivers both on the ground and in the plane to track the position of the instrument. That’s where I come in. I set up the GPS ground station, which consists of GPS receivers and an antenna. In the field we usually get a rundown shack and we have to set up our own antenna. The Wallops GPS building was luxurious in comparison. It was spacious, air-conditioned, and had a permanent antenna built in, which meant I didn’t have to set up a tripod. I hooked up three ground receivers to the antenna, verified that they were working and started recording data. We do this for up to five days, in order to calculate precisely the location of the ground antenna.

GPS receiver

GPS receiver aboard the NASA C-130 set up for testing

I also tested the GPS antenna on the plane. It’s a different model from the ground antenna and is bolted to the top of the plane. A cable runs down from it so we can hook up the receivers. Just like for the ground receivers, I verify that they are working and recording data correctly.

GPS antenna

GPS antenna aboard the C-130

The C-130 is a rugged cargo plane. One of our instrument racks, filled with equipment necessary to operate LVIS, was sitting on the hangar floor outside the plane, waiting to be moved into place and bolted down. I got a look at the current state of the in-flight facilities and took pictures for the team back home. There had been much discussion on the subject since some of our flights may last up to 10 hours. We never imagined we’d be discussing these issues when we were in school! It’s all part of the field work experience.

Antenna and receiver connected

GPS antennas and receiver wired up in the C-130 ready for test flights

At the end of the day, I collected and verified the GPS data available and left the ground receivers running. Everything was working as expected, so it was time for me to make the three hour trek back home. No traffic and beautiful scenery made for a pleasant drive.

SEAT: Satellite Era Accumulation Traverse: Ice cores: From Antarctica to the lab

November 4th, 2011 by Maria-Jose Viñas

By Lora Koenig

Two weeks ago, I traveled to Utah to help the team finalize planning for this season and to visit the ice core lab and our 2010 ice cores at BYU. The entire was there, except for Ludo, who was in Hawaii competing in a triathlon. (Ludo is not only a top scientist but a top triathlete. I hope he is not getting too use to the warm weather because in less than a month he will be facing temperatures around 0°F.)

There were a few tasks to complete in Utah. The first was to look at many different types of satellite data on the region where we will be traveling to make sure there aren’t any crevasses or other dangers along the route. A crevasse is a crack in the ice. As the ice flows (yes, ice flows just like a mound of putty), it can crack when it goes over a bump or accelerates. Here is a recent picture of crevasses in Western Antarctica, from a NASA Operation IceBridge flight.

Photo Credit: Michael Studinger/NASA

As you can imagine, we would not want to drive a snowmobile in an area like this. So we spent hours looking over maps of the rock bed under the ice sheet to look for bumps, visible and radar satellite images of the surface of the ice sheet, and satellite data showing the velocity of ice flow to make sure that we are traveling on the safest possible route. We ended up moving one ice core drilling location slightly to avoid a dark spot that we could not clearly identify in one of the radar images, just to be extra cautious. Once the route was established, we generated waypoints (coordinates) every kilometer to load into the GPS units that we will use for navigation. The place we are going to is big, white and flat: It is very easy to lose your sense of direction, so we rely heavily on GPS units for navigation.

For some great images and videos on how ice flows in Antarctica please check out this video, made by our NASA colleague Eric Rignot who (thanks again, Eric!) also checked the data that sits behind these videos to help ensure our safe route.

If you would like an in-depth look, this file, which opens on Google Earth, shows our final route with points every 1 km.

Our second task in Utah was to visit last year’s ice cores and have our first meeting to discuss the initial data coming from them. First, here is a picture of a core in the field, taken in December 2010.

In this photo, Michelle (right) is labeling the core and I (left) am getting the core tube ready for storage. The arrow on the ice core bag shows which direction is up.  It is very important that all the cores are labeled in order, or we would lose our time series. The metallic tube in the center left of the picture protects the core during shipping. The core in the tube gets placed in the white core box sitting open on the left side of the picture. (Also, notice that Michelle is standing on a bright green pad to help insulate her feet from the cold snow. It’s a veteran trick for keeping your toes warm.)

Here is that same core in the lab today.

Summer is holding what was about 8 feet of the core and the rest of the about 50 feet of core is stacked in the boxes behind her, waiting for analysis.

Here is a very basic explanation of what happens to the cores once they arrive at Summer’s lab at BYU. (Normally, Summer would be the one writing this, but she is currently studying glaciers in Bhutan.)

When the core arrives, we put it in the freezer.  Here is Landon peering out of the freezer door:

In the freezer, we weigh the core to determine its density and measure its electrical conductivity, which tells us about its chemical composition. A volcanic event would be detected in the cores by the electrical conductivity and can be used to set a point in time. We take all these measurements twice, or even three times, to make sure they are accurate.

Here is a picture of a core that Landon is preparing, sitting on the freezer’s core handling tray:

This freezer is set to -4°F, so when not posing for a picture, Landon would normally be in a parka with gloves on.  As you can see, the core is still in its protective bag, which will be removed when actually processing the core. From here, the core is cut up into sections less than an inch (2 cm) long, and melted for the next stage of analysis.

I will add a quick note here that on last year’s traverse Landon was our lead driller. Both Landon and Jessica are masters students at BYU. They are not only integral players of the field teams, but are also the lead students for the lab analysis of these cores.

Once we have melted the core and put it in a bottle, we send it over to Jessica.

Here is Jessica operating the mass spectrometer (black box to the left in the picture with the blue screen) that will measure the stable water isotopes used to date the core. The isotopes in the snow have an annual cycle and it is this cycle that determines age of the core.  An isotope is an atom, in our case an oxygen atom, that has different variations with different number of neutrons and atomic numbers.  Oxygen has three stable isotopes: 16O, 17O, and 18O.  The peaks and valleys in the ratios of 18O/16O reflect the warmer (summer) and cooler (winter) temperatures, respectively.   Once the mass spectrometer determines the number of isotopes, we can establish the age of the core, in a way similar to counting tree rings. During this process, the core is in the little blue vials just to the right of Jessica.

After spending some time in the lab, we looked at the data from the first core that has been analyzed.  At this point the density and isotopes have been measured and Summer is carefully working to put together the depth-age scale, which is the age of the core at each depth where the core use to sit in the ice sheet.  I will use the density data from the core to determine an age-depth scale from the layers in the radar data and if all goes well the radar and ice core will line up giving us confidence in our analysis.

Last Monday, when I returned to Goddard, I had received my travel itinerary.  We will be leaving the U.S. on Nov 17th to make our journey down to Antarctica.  With all of this preparation, I am eagerly awaiting getting my feet on the Ice.