ICESat-2 (Ice, Cloud, and land Elevation Satellite 2), part of

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

's Earth Observing System, is a

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioiso ...

mission for measuring

ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at La ...

elevation and

sea ice thickness Sea ice thickness spatial extent, and open water within sea ice packs can vary rapidly in response to weather and climate. Sea ice concentration are measured by satellites, with the Special Sensor Microwave Imager / Sounder (SSMIS), and the ''Europ ...

, as well as land

topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sc ...

, vegetation characteristics, and clouds. ICESat-2, a follow-on to the ICESat mission, was launched on 15 September 2018 onboard

Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas. Delta II was part of the Delta rocket family and entered service in 1989. Delta II vehicles included the Delta 6000, and the two later Delta 7000 va ...

as the final flight from

Vandenberg Air Force Base Vandenberg may refer to: * Vandenberg (surname), including a list of people with the name * USNS ''General Hoyt S. Vandenberg'' (T-AGM-10), transport ship in the United States Navy, sank as an artificial reef in Key West, Florida * Vandenberg Sp ...

in California, into a near-circular, near-

polar orbit A polar orbit is one in which a satellite passes above or nearly above both poles of the body being orbited (usually a planet such as the Earth, but possibly another body such as the Moon or Sun) on each revolution. It has an inclination of about ...

with an altitude of approximately . It was designed to operate for three years and carry enough propellant for seven years. The satellite orbits Earth at a speed of . The ICESat-2 mission is designed to provide elevation data needed to determine ice sheet

mass balance In physics, a mass balance, also called a material balance, is an application of conservation of mass to the analysis of physical systems. By accounting for material entering and leaving a system, mass flows can be identified which might have b ...

as well as vegetation canopy information. It will provide topography measurements of cities, lakes and reservoirs, oceans and land surfaces around the globe, in addition to the polar-specific coverage. ICESat-2 also has the ability to detect seafloor topography up to 100 feet (30m) below the surface in clear watered coastal areas. Because the great changes of polar ice cover in

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

are not quantified, one of the main purposes of ICESat-2 is measuring the changing of the elevation of ice sheets by its laser system and lidar to quantify the influence of melting ice sheet in sea-level raising. Additionally, the high accuracy of multiple pulses allows collecting measurement of the heights of

sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's o ...

to analyze its change rate during the time. The ICESat-2 spacecraft was built and tested by

Northrop Grumman Innovation Systems Northrop Grumman Innovation Systems (NGIS) was a sector (business segment) of Northrop Grumman from 2018 through 2019. It was formed from Orbital ATK Inc. a company which resulted from the merger of Orbital Sciences Corporation and parts of Alli ...

in Gilbert, Arizona, while the on board instrument, ATLAS, was built and managed by

Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...

Greenbelt, Maryland Greenbelt is a city in Prince George's County, Maryland, United States, and a suburb of Washington, D.C. At the 2020 census, the population was 24,921. Greenbelt is the first and the largest of the three experimental and controversial New Dea ...

. The ATLAS instrument was designed and built by the center, and the

bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...

was built by and integrated with the instrument by

Orbital Sciences Orbital Sciences Corporation (commonly referred to as Orbital) was an American company specializing in the design, manufacture, and launch of small- and medium- class space and launch vehicle systems for commercial, military and other governmen ...

(later

Orbital ATK Northrop Grumman Innovation Systems (NGIS) was a sector (business segment) of Northrop Grumman from 2018 through 2019. It was formed from Orbital ATK Inc. a company which resulted from the merger of Orbital Sciences Corporation and parts of Alli ...

). The satellite was launched on a

rocket provided by

United Launch Alliance United Launch Alliance (ULA), legally United Launch Alliance, LLC, is an American spacecraft launch service provider that manufactures and operates a number of rocket vehicles that are capable of launching spacecraft into orbits around Earth, a ...

. This was the last launch of the Delta II rocket.

Satellite instruments

The sole instrument on ICESat-2 is the Advanced Topographic Laser Altimeter System (ATLAS), a space-based

lidar Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...

. It was designed and built at Goddard Space Flight Center, with the laser generation and detection systems provided by Fibertek. ATLAS measures the travel time of laser photons from the satellite to Earth and back; computer programs use the travel time from multiple pulses to determine elevation. ATLAS emits visible laser pulses at 532 nm wavelength. As ICESat-2 orbits, ATLAS generates six beams arranged in three pairs in order to better determine the surface's slope and provide more ground coverage. Its predecessor, ICESat, had only one laser beam. The greater number of lasers allows for improved coverage of Earth's surface. Each beam pair is apart across the beam track, and each beam in a pair is separated by along the beam track. The laser array is rotated 2 degrees from the satellite's ground track so that a beam pair track is separated by about . The laser pulse rate combined with satellite speed results in ATLAS taking an elevation measurement every along the satellite's ground path. The laser fires at a rate of 10 kHz. Each pulse sends out about 200 trillion photons, almost all of which are dispersed or deflected as the pulse travels to Earth's surface and bounces back to the satellite. About a dozen photons from each pulse return to the instrument and are collected with a

beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to for ...

telescope. Beryllium has high

specific strength The specific strength is a material's (or muscle's) strength (force per unit area at failure) divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio or strength-to-mass ratio. In fiber or textile applic ...

and holds its shape across a large range of temperatures. The telescope collects photons with wavelength of 532 nm, thus filters out irrelevant light in the atmosphere. Computer programs further identify 532 nm photons in the dataset; only reflected photons of the laser are kept for analysis. A notable attribute of ATLAS is that engineers enabled the satellite to control how it is positioned in space, which is relevant because ATLAS records the distance from itself to the ground, and if its position is off, the measurement recorded for Earth's elevation will be off as well. Engineers also constructed the laser reference system, which confirms that the laser is adjusted in accordance to the telescope. If either the telescope or the laser is off, the satellite can make its own adjustments accordingly. The

National Snow and Ice Data Center The National Snow and Ice Data Center (NSIDC) is a United States information and referral center in support of polar and cryospheric research. NSIDC archives and distributes digital and analog snow and ice data and also maintains information abo ...

Distributed Active Archive Center manages ICESat-2 science data.

Mission science

ICESat-2 has four science objectives: # Quantify polar ice sheet contributions to current and recent sea-level change and the linkages to climate conditions; # Quantify regional signatures of ice-sheet changes to assess the mechanisms driving those changes and improve predictive ice sheet models; this includes quantifying the regional evolution of ice sheet changes, such as how changes at outlet glacier termini propagate inward; # Estimate sea-ice thickness to examine ice/ocean/atmosphere exchanges of energy, mass and moisture; # Measure vegetation canopy height as a basis for estimating large-scale biomass and biomass change. For this mission, the data of heights of vegetation canopy are highly accurate by using the multibeam system and micropulse lidar (photon-counting) technology in Advanced Topographic Laser Altimeter System (ATLAS). In addition, ICESat-2 will take measurements of clouds and aerosols, the height of oceans, inland water bodies like reservoirs and lakes, cities, and ground movements after events like earthquakes or landslides.

Project development

ICESat-2 is a follow-up to the original ICESat mission, which was decommissioned in 2010. When the project entered its first phase in 2010, it was expected to be ready for launch as soon as 2015. In December 2012, NASA reported that they expected the project to launch in 2016. In the following years, technical issues with the mission's only onboard instrument, ATLAS, delayed the mission further, pushing the expected launch back from late 2016 to May 2017. In July 2014, NASA submitted a report to Congress detailing the reasons for the delay and a projected budget overrun, as is required by law for NASA projects which spend at least 15% over budget. In order to finance the budget overrun, NASA diverted funds from other planned satellite missions, such as the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite. The launch of ICESat-2 took place on 15 September 2018 at 15:02 UTC from

Space Launch Complex 2 aboard a

7420-10C. To maintain a degree of data continuity between the decommissioning of ICESat and the launch of ICESat-2, NASA's airborne

Operation IceBridge Operation IceBridge is an ongoing NASA mission to monitor changes in polar ice. It is an airborne follow-on mission to the ICESat satellite, continuing until after the ICESat-2 mission launch in September 2018. Program history From 2003 to ...

used a variety of aircraft to collect polar topography and measure ice thickness using suites of laser altimeters, radars, and other systems.

Applications

ICESat-2's Applications program is designed to engage people and organizations who plan to use the data, before the satellite launches. Selected from a pool of applicants, this Science Definition Team represents experts in a wide variety of scientific fields including hydrology, atmospheric science, oceanography, and vegetation science. Early Adopters in the program, including ice scientists, ecologists, and the Navy, work with the ICESat-2 applications team to provide information on how the satellite observations can be used. The goal of this group is to communicate the vast capabilities of the ICESat-2 mission with the greater scientific community, with the aim to diversify and innovate new methods and techniques from the collected data. For example, scientists in the ecology field will be able to use the measurement of vegetation height, biomass, and canopy cover derived from ICESat-2's photon counting lidar (PCL). In the spring of 2020, NASA selected the ICESat-2 Science Team through a competitive application process, to replace the pre-launch Science Definition Team. This group acts as an advisory board to the mission post-launch, in an effort to ensure the mission science requirements are met.

References

External links