Notes from the Field

Boreal Summer

September 12th, 2023 by Fred Huemmrich and Petya Campbell, University of Maryland BalHmore County

Fieldwork notes, July 21-August 3, 2023

Summer fieldwork for our project, “Clarifying Linkages Between Canopy Solar Induced Fluorescence (SIF) and Physiological Function for High Latitude Vegetation,” once again took our team from University of Maryland Baltimore County north to the boreal forests of central Alaska. We visited this area in the spring to collect data during the very start of the growing season, and now we are returning to collect data during the peak of summer.

This project is part of the NASA Terrestrial Ecology program’s Arctic-Boreal Vulnerability Experiment (ABoVE). The goal of ABoVE is to improve our understanding of high latitude ecosystems, how these ecosystems respond to climate change, and how satellite data can provide information to describe ecosystem processes and aid management decisions.

Our study focuses on measuring light emitted by plants called solar induced fluorescence. Green leaves absorb light, and through photosynthesis take in carbon dioxide and water and produce oxygen and sugars. Fluorescence occurs during photosynthesis as some of the absorbed light energy is radiated out from the plant. The amount of light fluoresced is only a very small fraction of what is absorbed, which is why our eyes don’t see plants glowing. In our study, we use sensitive instruments that can detect this fluorescence. Our goal is to better understand the sources of fluoresced light and how to use this information to describe productivity in boreal forests and tundra.

Our study site is at the Caribou Creek flux tower run by the National Science Foundation’s National Ecological Observatory Network (NEON). In spring, we deployed automated instruments at the NEON tower site that continuously collect data. On this trip, we are checking on how they have been working.

In July there was a big change from our previous visit in April. In April, the area had a deep snow cover with temperatures dropping below 0°F, while during this visit the daytime temperatures were in the 80s F and the ground was now all green (images below).

The gated bridge at the entrance to the Caribou-Poker Creeks Research Watershed where we are working in the spring and summer.

The boreal forest landscape in the Caribou creek with a view of the NEON tower in the black spruce forest.

On the top of the tower we have an instrument called a FLoX (Fluorescence Box). The FLoX views a patch of forest from above, and every few minutes during the day it measures the reflected light and solar induced chlorophyll fluorescence. This provides us with a description of plant activity at different times of the day through the growing season (images below).

The boreal forest at our study site (top-left). Looking up at the NEON flux tower, the thin pole extending from the top of the tower is from the FLoX (top-right); looking down from the top of the tower at the pole from the FLoX and the boreal forest below (bottom-right); and Petya and Fred with our safety gear on (bottom-right).

Also at the site we have monitoring PAM (MoniPAM) instruments attached to shoots of the spruce trees. The MoniPAM probes shine pulses of light at individual spruce shoots to measure fluorescence and photosynthetic processes at the leaf level (images below). We put blankets over the probes for a while to dark-adapt the shoots to measure their response when unstressed. In the spring, we put the MoniPAM probes in easy-to-reach places when there was a lot of snow on the ground. On this trip, when we returned to check them in the summer, we found we had to really reach up to get them without the snow to stand on.

MoniPAMs measure fluorescence of individual spruce shoots to describe photosynthetic processes. MoniPAM probe on a spruce tree views the spruce needles inside the clip (left); Bue blankets hang on the trees to cover the MoniPAM probes to dark adapt the shoots during the day (right).

One of the great things about working in the boreal forest in summer is that there are yummy berries to snack on, such as cloudberry (left) and blueberries (right).

From the ground, we collected reflectance and fluorescence measurements (similar to the data collected by the FLoX) of individual plants in the FLoX field of view and a variety of representative plants in the larger area surrounding the tower. These measurements will help us understand the local variability (images below).

A lot of the ground cover was cotton grass (Eriophorum spp.) that forms tussocks, which are tight clumps of grasses. The tussocks made walking through the area difficult, like walking on half-buried basketballs, so it was easy to twist an ankle, especially with a heavy backpack spectrometer on your back.

Measuring reflectance and fluorescence of different types of boreal forest plants. Collecting measurements at the base of the tower in the footprint of the FLoX (top-left); using the STELLA (top-right)—a multiband radiometer you can build yourself; and collecting data from a variety of different plants near the tower site (bottom).

Going into the field, you need to be prepared for pests both large (bear spray, that was never used) and small (mosquito repellent, which was heavily used).

We collected branch samples to make measurements of leaves and needles that we will use to parameterize models of vegetation fluorescence and productivity (images below).

Measuring leaf samples in our hotel room. Measuring photosynthesis rates (top-left); measuring leaf chlorophyll (top-right); measuring leaf level reflectance and fluorescence spectra (bottom-left); and the variety of different species we sampled (bottom-right).

We took a little time off to visit some other places in the area. We saw musk ox, which are animals of the tundra but raised in captivity at the University of Alaska Fairbanks’ Large Animal Research Station. Their thick, shaggy coat keeps them warm through the frigid arctic winters. Under the long guard hairs is a soft wool called qiviut that musk oxen shed in the spring. Qiviut can be spun into a very warm and soft yarn. Small balls of qiviut yarn can sell for over $100.

Musk ox at the University of Alaska Fairbanks Large Animal Research Station.

On our last day in Alaska we visited the Cold Regions Research and Engineering Laboratory (CRREL)  Permafrost Tunnel Research Facility (images below). Permafrost refers to soil that has been frozen continuously for more than two years. The permafrost around Fairbanks, Alaska, is considered ‘warm’ (at a temperature of -0.3oC/-0.4oC) as compared to the permafrost in our other study site in the North Slope of Alaska at Utqiagvik (e.g., a temperature -3oC/-4 oC). This warm permafrost is very sensitive to the changes in soil temperatures that can result from fires, rain events, and other disruptions that can cause permafrost thawing. Thawing permafrost can result in damage to roads and buildings and cause disturbance in forests.

The permafrost tunnel is dug into a hillside through earth that has been frozen for thousands of years. The tunnel reveals bones of extinct ice age animals, plants preserved since the ice age, and large ice wedges that can take hundreds to thousands of years to form. The ice wedges cause the formation of polygonal patterned ground, where the ground surface is covered with a pattern of shapes of slightly higher or lower ground. Our study site in Utqiagvik was in an area of high centered polygons, so it was interesting to be able to actually see the shapes of the underground ice that formed that unique landscape.

Looking down the permafrost tunnel (left) and a large ice wedge exposed in the tunnel (right).

Expedition to Alaska’s Burned Tundra

August 8th, 2023 by Max van Gerrevink, Ph.D. student at Vrije Universiteit Amsterdam
Part of our team at a burned tundra site from the 2022 East Fork fire in Southwest Alaska. From left to right: Sander Veraverbeke, Max van Gerrevink, Lucas Ribeiro Diaz, Sonam Wangchuk, and Thomas Janssen. Rebecca Scholten and Thomas Hessilt will join later in the campaign.

In 2022, severe lightning ignited many fires in Alaska. Notably, several exceptionally large fires burned in the tundra of Southwest Alaska, an ecosystem that is traditionally less prone to fire. While our understanding of the carbon emissions of boreal forest fires in Alaska and Canada has strongly advanced in recent years thanks to the work of several teams within NASA’s Arctic-boreal Vulnerability Experiment (ABoVE), the impacts of these tundra fires on the ecosystem’s carbon balance and permafrost has remained less well known.

Our Climate and Ecosystems Change research group from the Vrije Universiteit Amsterdam in the Netherlands is currently in Southwest Alaska to fill these critical knowledge gaps. Our team received tremendous help of Dr. Lisa Saperstein from the Alaska Fish and Wildlife Service in organizing the campaign. Lisa will also start a field campaign in the same fires in the next few days and we plan to pool our datasets to maximize synergies between our efforts.

The 2022 East Fork and the Apoon Pass fires together burned more than 100,000 hectares (380 square miles) of primarily tundra landscapes in Southwest Alaska. They were among the largest tundra fires on record for the region.

Our basecamp is the village of St. Mary’s, located just west of the East Fork fire on the Andreafsky River. For the first part of our campaign, we are taking a boat upstream to access the fire scar. We are looking for burned tussock tundra sites, where we can measure the effects of the fire on the vegetation, soils, and permafrost in our plots. We are also sampling unburned tundra sites, which provide us a reference of the conditions without fire disturbance. During the last part of our campaign we will access sites in the remote Apoon Pass fire by helicopter.

Max van Gerrevink measuring the depth of burning in the organic soil using an unburned tussock as a reference. These measurements will reconstruct carbon combustion in our sites.

The local community heavily relies on the landscape for subsistence activities, like hunting and berry picking. Our boat driver, Matty Beans, is native to the area and is extremely helpful in bringing us to the right places. A large concern of the community is how the fire has effected the abundance of berries in the burned tundra. Our preliminary observations indicate that the cloudberries, locally also called salmonberries, were abundantly present in the burned sites. However, this was not the case yet for blueberries.

Presence of cloudberries, locally referred to as salmonberries, in one of our burned sites.

So far, we have been extremely lucky with mostly dry weather and only a little bit of rain. However, the dry weather has affected the water levels in the Andreafsky River. We came across collapsed river banks and exposed sand banks in the river. Our boat driver has switched to his jet boat so that we can continue on, even in more shallow parts of the river. The weather is changing though, with rain coming in for several days. This is good for the water levels, but the colder and rainy weather may make our sampling efforts more challenging.

After seven days and 19 plots of sampling, we are now taking a well-deserved rest day. I used this rest day to write this blog and digitize some datasheets. Over the next four days, we will continue sampling along the river and then use a helicopter to access the Apoon Pass fire site for more sampling.

A view on the Andreafsky River from one of our burned sampling sites.

This field expedition is part of FireIce (Fire in the land of ice: climatic drivers & feedbacks). FireIce is a Consolidator project funded by the European Research Council. FireIce is affiliated with NASA ABoVE.

G-LiHT Goes to Alaska

January 26th, 2023 by Allison Nussbaum

In loving memory of Larry Corp.

What is G-LiHT?

Goddard’s LiDAR, Hyperspectral, & Thermal Imager (G-LiHT) is an airborne instrument designed to map the composition of forested landscapes.

The G-LiHT instrument has a number of sensors that each serve a specific purpose. There are two LiDAR sensors that produce a series of LiDAR-derived forest structure metrics including a canopy height model, surface model, and digital terrain model. These models allow us to measure tree height and biomass volume.

Additionally, there are two cameras: one visible and one near-infrared (NIR). The visible and NIR bands acquired by the two cameras are paired to produce 4-band imagery. The 3-centimeter resolution photos taken by these cameras are aligned to build orthomosaics, which allow us to visually observe and identify changes in forest composition.

G-LiHT also has a hyperspectral sensor to acquire spectral information at a coarser resolution. These data can be used to identify vegetation composition and measure photosynthetic function as well as calculate vegetation indices at a fine spectral scale of 1 meter using radiometrically calibrated surface reflectance data.

The thermal sensor measures radiant surface temperature which allows us to create 3D temperature profiles derived from structure-for-motion. Thermal data provides us with information on the functional aspects of forest canopies. As photosynthetic function is related to evapotranspiration, we can observe that hotter canopies are more stressed relative to surrounding canopies.

Purpose of the field campaign

The G-LiHT airborne mission supports multiple groups including the U.S. Forest Service (USFS), the USFS Geospatial Technology and Applications Center (GTAC), and the University of Alaska Anchorage.

The USFS is creating a forest inventory for the state of Alaska, and G-LiHT measurements collected over Forest Inventory and Analysis (FIA) plots are a cost-effective method of forest inventory. G-LiHT data will also help to improve regional estimates of aboveground forest biomass and terrestrial ecosystem carbon stocks. GTAC uses G-LiHT data measurements for algorithm development. USFS Geospatial Technology and Applications Center will use G-LiHT data acquired over FIA- and GTAC-measured ground plots and between these plots to map forest characteristics on federally managed lands, including forest type, biomass, vegetation structure, tree and shrub cover, and more. Data will also be used to guide future inventory efforts in coastal Alaska using methods developed for interior Alaska.

This field campaign also acquired repeat data over Fairbanks, Alaska, to measure changes in permafrost.

G-LiHT image data was reacquired over spruce beetle monitoring transects stretching from the Kenai Peninsula in the south to Denali National Park in the north. These transects were last measured on the ground and with G-LiHT in 2018, during the peak of a spruce beetle outbreak, and changes in vegetation structure and spectral reflectance will be used to evaluate the long-term mortality and growth of these forests.

Integrative test flight

Our Alaskan field campaign started with an integrative test flight in June. Our team of three loaded up G-LiHT into a vehicle much too small and drove to Dynamic Aviation in Bridgewater, Virginia. We spent the first day installing the instrument into a 1960s King Air A90.

King Air A90 and the G-LiHT team, from left to right: Lawrence Corp (SSAI), Bruce Cook (NASA), and Allison Nussbaum (SSAI).

The second day was all about flying. We needed to make sure G-LiHT didn’t interfere with any of the aircraft’s systems. Additionally, the functional test flight over Harrisonburg, Virginia, allowed us to verify that G-LiHT was functioning properly. We flew in a grid pattern over the city which allowed us to geospatially align the data products from all of G-LiHT’s sensors.

1,100-foot view of Harrisonburg, Virginia.

The integrative test flight was a success. We installed G-LiHT properly with no issues and obtained the information we needed. Once we received the thumbs up to proceed with our campaign, the pilots loaded up the plane with supplies and headed out to Kodiak, where we would meet them the following week.


Our plan for the field campaign was to arrive in Kodiak, Alaska on July 6 and stay until the end of the month. We chose Kodiak as our hub because it was a convenient location to our flight lines. Unfortunately, despite the ideal location, poor weather prevented us from flying for the first three days of the campaign.

Much of the island, including the marina across the street from our hotel, was covered in a blanket of fog.

Once we were finally able to get in the air, we collected data over the forests near Iliamna.

Forests to the south of Iliamna Lake.

Bruce Cook (NASA) and Lawrence Corp (SSAI) monitoring incoming data via a fold-out monitor connected to computers on G-LiHT.

Lawrence Corp (SSAI) and Allison Nussbaum (SSAI) monitoring real-time G-LiHT hyperspectral data (left monitor) and near infrared and visible photos (right monitor).

Most of our days consisted of our team meeting in the hotel for breakfast at 8 a.m., discussing weather and flight plans for the day, and then driving to the airport to prepare the plane and G-LiHT for flying. Depending on how many flight lines we were able to complete, we often stopped in King Salmon or Iliamna to refuel the plane and then went back out to fly more lines before returning to Kodiak.

Refueling in King Salmon, Alaska. From left to right, FO Nathan Bierman (Dynamic Aviation),
Captain Paul Ciaramitaro (Dynamic Aviation), Bruce Cook (NASA), Allison Nussbaum (SSAI), and Lawrence Corp (SSAI).

Our group was interested in measuring the effects of forest fires on vegetation in the Dillingham region. There were several burned areas to the west of the Nuyakuk River and east of Cook Inlet.

Photo from plane of burn scars east of Lake Clark National Park and Preserve (left) and photo of burn scars captured by G-LiHT (right).

Freshwater lakes on top of a mountain west of Hidden Bay on Kodiak Island, Alaska.

Toward the end of the campaign, we decided to transit to Fairbanks because the weather over the rest of our other flight lines didn’t look promising. If there were clouds below the plane at 1,100 feet, they would obstruct the instrument’s view and cast shadows on our data. We had to closely monitor the weather every morning. Additionally, we were unable to fly in rain or smoke as it would adversely affect the LiDAR sensors’ data returns.

Bruce Cook (NASA) viewing real-time LiDAR data acquisition.

One geological feature we saw extensively in the southwest was the oxbow lake. Also called cut-off lakes, these lakes have formed when meandering rivers erode at points of inflection because of sediments flowing along them to the point where two parts of the river will join together, creating a new straight part of the river—essentially “cutting off” the curved lake piece. This created an oxbow lake. Once the lake has fully dried out, it becomes a meander scar. We noted the difference in vegetation growing back within the oxbow lakes and meander scars and how this differs from surrounding vegetation patterns.

Oxbow lake on the Tanana River in Fairbanks, Alaska.

We had only planned to spend one night in Fairbanks, then transit back to Kodiak the following day. However, the weather had other plans for us. We ended up having to fly to Anchorage the following day because of extremely low cloud ceilings in Kodiak that made it too dangerous to land there. It worked out in the end, and the team was able to see more of beautiful Alaska and collect data over Anchorage and the Chugach region. It just goes to show how quickly things can change during a field campaign.

Chugach Mountains seen from King Air.

We collected data in the Campbell Creek region west of Anchorage. The data include visible and near-infrared photos which were composited into 4-band high-resolution orthomosaics and used to visually observe and identify changes in forest composition.

Orthomosaic of Campbell Creek area acquired by G-LiHT.

In addition to the high-resolution orthomosaics produced from the G-LiHT’s near-infrared and visible cameras, LiDAR data was processed to create various 1-meter resolution forest structure metrics including Digital Terrain Model (DTM), Digital Surface Model (DSM) and Canopy Height Model (CHM). These metrics are used to measure tree height and biomass volume. The CHM raster below was created by subtracting the DTM from the DSM.

After collecting data in Anchorage and the Chugach region of Alaska, the team flew back to Kodiak and finished data acquisition in the southwest.

Map of completed flight paths for the 2022 G-LiHT Alaska field campaign.

And of course it wouldn’t be Alaska without some wildlife. The day before leaving Kodiak, I got to see not just one bear—but a family of four! Cars were honking to scare the bears out of the road, but luckily I had enough time to snap a picture before the bears ran off into the woods. It was the perfect end to an exciting field campaign.

A mother bear and her cubs on the side of the road in Kodiak.

Happy Sixth Birthday to the CYGNSS Constellation

December 15th, 2022 by Chris Ruf

It’s been six years since the CYGNSS constellation was launched. Over that time, it has grown from a two-year mission measuring winds in major ocean storms into a mission with a broad and expanding variety of goals and objectives. They range from how ocean surface heat flux affects mesoscale convection and precipitation to how wetlands hidden under dense vegetation generate methane in the atmosphere, from how the suppression of ocean surface roughness helps track pollutant abundance in the Great Pacific Garbage Patch to how moist soil under heavy vegetation helps pinpoint locust breeding grounds in East Africa. Along with these scientific achievements, CYGNSS engineering has also demonstrated what is possible with a constellation of small, low cost satellites.

Artists rendering of the CYGNSS constellation of smallsats, with specular reflection tracks highlighted,

As our seventh year in orbit begins, there is both good news about the future and (possibly) bad news about the present. First the bad news. One of the eight satellites, FM06, was last contacted on 26 November 2022. Many attempts have been made since then, but without a response. There are still some last recovery commands and procedures to try, but it is possible that we have lost FM06. The other seven FMs are all healthy, functioning nominally and producing science data as usual. It is worth remembering that the spacecraft were designed for 2 years of operation on orbit and every day since then has been a welcomed gift. I am extremely grateful to the engineers and technicians at Southwest Research Institute and the University of Michigan Space Physics Research Lab who did such a great job designing and building the CYGNSS spacecraft as reliably as they did. Let’s hope the current constellation continues to operate well into the future.

And finally, the good news is the continued progress on multiple fronts with new missions that build on the CYGNSS legacy. Spire Global continues to launch new cubesats with GNSS-R capabilities of increasing complexity and sophistication. The Taiwanese space agency NSPO will be launching its TRITON GNSS-R satellite next year, and the European Space Agency will launch HydroGNSS the year after. And a new start up company, Muon Space, has licensed a next generation version of the CYGNSS instrument from U-Michigan and will launch the first of its constellation of smallsats next year.

The CYGNSS team will continue to operate its constellation, improve the quality of its science data products, and develop new products and applications for them, with the knowledge that what we develop now will continue to have a bright future with the missions yet to come. Happy Birthday, CYGNSS!


July 21st, 2022 by Alex Haughton

Alex Haughton is a graduate student in the Astrophysical and Planetary Sciences department at University of Colorado Boulder studying ultraviolet instrumentation with sounding rockets. His team has traveled to Equatorial Launch Australia’s Arnhem Space Center near Nhulunbuy, Australia to launch the Dual-channel Extreme Ultraviolet Continuum Experiment (DEUCE) Sounding Rocket and observe the stars Alpha Centauri A & B in extreme ultraviolet wavelengths.

The light of a waxing gibbous illuminates the eucalyptus forests of East Arnhem Land. A mild breeze rustles the trees, and clouds pass overhead, first obscuring and then revealing Alpha Centauri A & B, our targets. A Hunstman spider we named “Jeremy,” recently displaced from its position guarding the detonator switch, scuttles along the ground near where the DEUCE payload stands vertical, perhaps moments away from being launched into space.

30,000 feet above this scene, a weather balloon floats, taking wind measurements and beaming them back down to the Range Control Center. The countdown is approaching T-minus two minutes, and range safety officer Brittany Empson concentrates on the wind readings. While the overall velocity of the winds has been low enough to continue, the variability of the winds this evening has been too high to launch – the tail end of a storm over Indonesia just clipping the Gove Peninsula where the launch range stands. Unless the variability goes down, Brittany will have to call for a hold, resetting the countdown to T-minus three minutes. Five seconds before she must make the call, the variability number drops into the green.

“RSO Check Item 140,” she announces. She continues watching the data come in – if it goes red anytime in the next two minutes, the count must be reset. Next to her, campaign manager Max King begins polling various people to “Report GO Status.” There’s a rhythm to it, exactly as you imagine from the movies:









And so on and so forth. A couple hundred meters away from the Range Control Center in the Command Uplink Facility (CUF), where the science team sits, chills run down my spine, and I do my best not to get emotional. Our team has been building to this moment for at least the past year, and more personally this night represents a dream come true for me. I’ve watched the two previous payloads launch, and while both of them were awesome, this time I’m in the room, and I have things to do. It’s real.

Dr. Brian Fleming, the principal investigator (the one who proposed the project and won funding to make it happen) announces “Go” for us. Also in the room are Emily Witt, the senior graduate student on the launch, Alex Sico, our technician, and Chris “Hox” Hoxworth, who runs the uplink equipment in the CUF and whose calming voice has guided many a graduate student through this stressful situation over the year. With 30 seconds left in the countdown, we scurry outside the CUF; our next responsibilities are one minute after launch.

We can’t see the rocket from our vantage point, as it is hidden behind trees, but we know in which direction it lies. The speakers on the range count out the last ten seconds, and the night seems to hold its breath in anticipation: “Ten, nine, eight, seven, six, five, four, three, two, one…”

The light comes first, a bright flare revealing the trees and the trucks, trailers and radar dishes, and then just as the top of the payload crests the trees the resounding wall of sound crashes into our ears.


The rocket flies up, up, and away, the first stage burning through its fuel in a mere six seconds before silence engulfs the night again and only an echo, perhaps real, perhaps imaginary, of that first guttural roar is left bouncing through my head. Emily and Brian quickly dash back in to get to their stations, but I linger a few seconds longer and catch the second stage of the rocket igniting before following them.

I check the screen I am assigned to watch: the numbers look not good but great – the temperatures and voltages are as they should be, even the vacuum gauge is reading surprisingly low. By 77 seconds into the flight the vacuum gauge finally starts increasing slightly before the shutter door opens and it drops back to zero. At this point the payload has separated from the two rocket motors and the Attitude Control System (ACS) begins pointing us towards our star. It appears on the touchscreen Emily uses to steer, and she leans into her screen, eager to move it to the correct place. She can’t quite yet, though: She has to wait for the ACS engineer, Brittany Barrett, to give her the go ahead. Excruciating seconds pass.

“ACS on target and ready for uplinks,” reports Ms. Barrett.

Emily quickly begins steering the telescope’s slit to align with the star, fingers flying over the screen: Target, Set, Send. Data is now coming in on the detector screen, and Brian begins reading out count numbers: more is better.

“132… 214… 189… 488… 603… 488… 603,” he reports. On the screen Emily has the star roughly aligned with the slit, but our pointing is a bit bouncy, so she is consistently nudging it back into line. Finally, a few minutes in, it largely settles where it is supposed to. On the data screen we watch as photons hit the detector, concentrating on the area where there should be spectral lines, the indication that we are getting data from the star and that the data will have interesting science results.

“There!” exclaims Brian, his finger indicating a region with more counts. “That’s a line. We have data!” There is still some tension in the room: Emily continues to nudge the star to get the best results, and Brian continues hunting for other obvious lines, but relief is starting to set in. We are getting what we came here for.

Seven minutes and six seconds after takeoff the shutter door closes. The payload reached its apogee of 258 kilometers and is falling back down to Earth. It will launch a parachute and hopefully land gently (some landings are gentler than others). We leave the CUF to head for the RCC, handshakes, hugs, and general celebration. Somewhere, Jeremy the Hunstman spider crawls away, seeking a hunting location unoccupied by space goers. The work isn’t done, but the scary part is. Success.