News - GLOBE Observer
Four Years of ICESat-2 and the Upcoming NASA GLOBE Trees Challenge 2022: Trees in a Changing Climate
What do trees, tree height, lasers, and a NASA satellite called the Ice, Cloud, and land Elevation Satellite-2 have in common?
Four years ago on 15 September, 2018, the NASA Ice, Cloud, and land Elevation Satellite-2 (ICESat-2), launched into space, onboard the last Delta-II rocket, from the Vandenberg Air Force Base (now the Vandenberg Space Force Base) on the central coast of California, USA. Since then, the Advanced Topographic Laser Altimeter System (ATLAS) instrument onboard ICESat-2 has fired trillions of laser shots (photons) towards Earth, in order to measure the elevation (height) of ice sheets, sea ice, glaciers, landforms, urban areas, cloud cover, sea surface (with potential shallow bathymetry) vegetation, trees, and more.
Since the launch of ICESat-2 four years ago, the satellite has measured the height of tens of millions of trees across the planet.
Some “Cool, Sciency Stuff” about ICESat-2
ATLAS carries two lasers, one primary and one backup. The laser light is set at 532 nanometers, which is a bright green color on the visible light spectrum. It is a fast-firing instrument – it sends 10,000 pulses per second!With this incredibly fast pulse rate, ATLAS can take measurements every 2.3 feet (0.7 meters) along the satellite’s ground path, allowing for dense, detailed data across the globe.
The photons that return to ATLAS’s telescope are focused on six fiber optic cables in the focal plane, corresponding with where the six laser beams will return. From those fibers, the photons pass through a series of filters, which only allow light that is at precisely 532 nanometers in order to prevent sunlight that naturally reflects off Earth from swamping the detectors.
When an individual 532-nm photon makes it through the filters, it triggers the detector. The timer, which started when the laser left the satellite, then stops.
A Little More About ICESat-2 and Measuring Tree Height
ICESat-2 provides scientists with height measurements that create a global portrait of Earth’s 3rd dimension. The purpose of gathering data is so that scientists can precisely track changes of terrain including glaciers, sea ice, vegetation, forests and more.
While many of ICESat-2’s discoveries are yet to be imagined, the satellite mission has four scientific objectives:
- Measure melting ice sheets and investigate how this affects sea level rise
- Measure and investigate changes in the mass of ice sheets and glaciers
- Estimate and study sea ice thickness
- Measure the height of vegetation in forests and other ecosystems worldwide
Other Earth-observing satellites, such as Landsat and MODIS, allow researchers to study the location and extent of forests; ICESat-2 allows them to add the height. Because ATLAS is sensitive enough to detect individual photons, and has such a rapid firing rate, the instrument is able to detect both the forest floor and the tops of canopies in all but the densest woods and jungles. With this information, scientists can calculate the amount of vegetation – the trunks, branches, leaves, shrubs and more – that make up an area’s biomass. Studying the gain or loss of biomass can inform calculations of the carbon that forests either take in or release into the atmosphere.
The NASA GLOBE Trees Challenge 2022: Trees in a Changing Climate
Following in the footsteps of the NASA GLOBE Land Cover Challenge 2022: Land Cover in a Changing Climate (26 July – 26 August 2022) is the NASA GLOBE Trees Challenge 2022: Trees in a Changing Climate. This important transition allows all of us to continue the observations of the environment around us by observing tree height and tree circumference using the NASA GLOBE Observer Trees tool. Since trees are a type of land cover, and tree height is a vital observation that NASA continues to observe from the ground and space, these observations are vital to NASA scientists and student researchers alike, and the data can be compared to the space-based tree height data from ICESat-2 and other NASA missions and instruments.
As for the actual observations, tree height is the most widely used indicator of an ecosystem’s ability to grow trees, so tracking tree height over time is a key factor to assessing the ecological health of a given area. Tree circumference can be used by foresters and managers to calculate the approximate age of the tree, and the measurements are also used to estimate the amount of standing timber in a forest. Additionally, both tree height and trunk circumference help to measure biomass, the total mass of living material above ground measured across a particular area. All these variables allow scientists to create global maps of land cover and forests and can help us understand how our planet is responding to a changing climate.
Just under one month prior to the start of the NASA GLOBE Trees Challenge 2022: Trees in a Changing Climate, the ICESat-2 Mission will be celebrating its 4th birthday in space. At 6:02 AM PDT (1:02pm UTC) on 15 September 2022, exactly 4 years to the minute, ICESat-2 will be flying just north of Antarctica, on its way towards the GLOBE Asia and Pacific Region.
With the 3.03 trillion trees and 78,000 tree species on Earth, we are constantly striving to add to the global inventory of tree height observations from space and to collect as many tree circumferences as possible. Scientists especially need measurements of multiple trees in areas that contain many trees. This is called “data density” and is a way for scientists to build a much more robust dataset of the tree heights from the ground and space. We are hoping that you will join us from 11 October – 11 November, 2022 and take as many tree height and tree circumference as you can.
Stay tuned to the NASA GLOBE Trees Challenge 2022: Trees in a Changing Climate by visiting the challenge website.
You can learn about the NASA ICESat-2 Mission at the mission's website.
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