National Academies Press: OpenBook

Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft (2021)

Chapter: 2 Setting the Stage: The Role of Airborne Platforms in Earth System Science

« Previous: 1 Introduction
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

2

Setting the Stage: The Role of Airborne Platforms in Earth System Science

This chapter provides an overview of Earth system science and the integrated observing system components used to study it. Within the integrated observing framework, airborne platforms, including piloted aircraft, uncrewed airborne systems (UAS), and balloons are discussed, along with the capabilities provided by the U.S. government airborne fleet. The development and evolution of instrumentation and how these changes in available equipment affect both the science questions and the aircraft capabilities required to fly them are also discussed.

2.1 FUTURE OF EARTH SYSTEM SCIENCE

The 2017-2027 Earth Science and Applications from Space Decadal Survey, ESAS, provides a roadmap to advance Earth system science and deliver critical information to support a broad range of economic and societal needs (NASEM, 2018a). It emphasizes that Earth is a dynamic planet on which the interconnected atmosphere, ocean, land, and ice interact across a range of spatial and temporal scales, irrespective of geographic, political, or disciplinary boundaries. In the future, more emphasis will be put on conducting NASA Earth system science research on the system level, with the aim of improving the understanding of the whole system comprising these elements, the processes that connect them, and the sensitivity of each element to changes in others.

For more than 50 years, airborne observations have contributed substantially to advances in the understanding of the Earth system. This progress has occurred across a wide range of current Earth system science disciplines. Because components of the Earth system are so interconnected, it is difficult to categorize science objectives by discipline. However, for this report, the committee organized the science research objectives for which airborne platforms can play a substantial role according to the ESAS priority science and applications areas. In addition to these science areas, there are critical and interdisciplinary Earth system science connections to which airborne observations contribute in concert with spaceborne and surface observations.

Improved understanding and more extensive observations of the Earth system are increasingly applied to societal and economic decision making. As this need expands and becomes more complex, Earth system observations and research must also advance to meet those needs. This will require an integrated Earth observing capability that builds on current and planned Earth system science research and observations. ESAS describes

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

some needs of importance: managing air pollution risks, water quality, and food security; improving prediction of extreme weather such as severe storms, tornadoes, hurricanes, winter storms, and wildland fires; measuring the health and productivity of land and oceans globally; assessing risks from sea level rise; and predicting large-scale geological hazards and studying impacts of geological disasters on the Earth system and society (NASEM, 2018a). All of these societally relevant issues rely on an integrated Earth system science research strategy that includes airborne science.

2.2 INTEGRATED EARTH SYSTEM SCIENCE RESEARCH

Because Earth is a complex, interconnected system, Earth system science research has developed an array of tools to understand it and its processes. The current integrated approach to Earth system science research involves observations from satellites, aircraft, the surface and subsurface, computer modeling, and laboratory studies (Figure 2.1).

Image
Figure 2.1 Conceptual diagram of integrated Earth system science research. The system includes numerous spaceborne observations from satellites and the International Space Station; airborne observations from piloted aircraft, uncrewed airborne systems, and balloons; surface and subsurface observations for land and water as well as remote sensing from the surface; computer models for Earth system simulation; and controlled laboratory experiments.
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

Satellites provide local to global measurements that are used for both scientific research and societal applications. Geostationary satellites measure many variables on a continental scale with good temporal resolution, while polar orbiting satellites provide near-global to global coverage of Earth’s surface and atmosphere every day or so. Measurements from both geostationary and polar satellites have been used to observe episodic extreme events and their impacts, such as volcanic eruptions, rapidly spreading wildland fires, and the Antarctic ozone hole. They are used to test computer models to improve model predictive capability and are assimilated into computer models to make predictions of weather and air quality. These satellite measurements are also used to monitor long-term trends, such as climate change, deforestation, changes in atmospheric pollutants, and shifts in weather patterns.

Airborne platforms carry instruments that provide targeted observations that complement satellite observations. These platforms include piloted aircraft, UAS of a wide range of sizes, and balloons and zeppelins. Targeted observations collected by these platforms can be either periodic, such as yearly surveys of forest health, or episodic, such as observing hurricanes approaching land, intensive studies of air pollution in megacities, land subsidence, landslide movement, and detailed measurements of ice sheet thickness and movement. Airborne platforms can also be deployed rapidly to respond to disasters such as volcanic eruptions, earthquakes, wildland fires, flooding, and oil spills.

Surface measurements comprise surface or near-surface measurements on land or water and upward remote sensing. Some surface measurements come from long-term networks built to monitor atmospheric and other surface or near-surface properties, including surface air temperature, precipitation, air pollution, water availability, ocean temperature and salinity, land motions, and seismic activity. Other networks monitor fluxes of carbon, water, and temperature within the planetary boundary layer (PBL) to understand ecosystem functioning. There are multiple regional networks, such as the widely used AmeriFlux network at Oak Ridge Distributed Active Archive Center, and complementary networks: Euroflux, OzFlux (Australia), ChinaFLUX, and many others. The National Science Foundation (NSF) National Ecological Observatory Network is operating a large network of about 80 sites. Upward-looking remote sensing networks monitor the atmosphere and sun for atmospheric composition, storms, and solar and atmospheric irradiance. Other measurements are less frequent and either targeted or semi-regular, such as ecological surveys of flora and fauna; intensive weeks-long studies of air, land, or water pollution; focused sensing of tectonic activity; and examination of ice cores for assessing past climate change.

Laboratory studies provide controlled experiments of Earth system processes, such as environmental effects on plant growth; the chemistry and physics of air, land, and water pollution; pollution effects on ecological and human health; mineral composition of rock and soil; and the microphysics of aerosol and cloud particles and their properties. In addition, they provide numerical values for factors that are used to interpret remote

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

sensing and in situ measurements collected on board the aircraft or from deployed instruments or to incorporate process rates into computer models.

Computer (or numerical) models simulate Earth system processes using numerical solutions of the governing equations. The goals of computer models are to improve the understanding of components of the Earth system and, in some cases, to provide predictions. Because of the complexity of many Earth system processes, their inclusion in models must be simplified and parameterized. A variety of models target individual processes on greatly different spatial and temporal scales, while others, such as climate models, incorporate representations of many different components of the Earth system, including the atmosphere, land, ocean, cryosphere, and ecological processes. Increasing model complexity is critical for accurately representing the Earth system as it is now and predicting its evolution resulting from internal forcing, such as increasing greenhouse gases, particularly those caused by humans, or volcanic activity, and external forcing, such as changes in solar radiation.

The way that observations, including space-based, airborne, surface, and subsurface measurements, laboratory studies, and computer models are used together depends on the research question that is being addressed. For different questions, each component of the integrated approach to Earth system science research brings unique value that cannot be provided by other means. This balance of components affects the way that observations are used by computer models, whether it is to improve computer model simulations of the Earth system or to be assimilated in computer models for making more accurate predictions.

2.3 ROLE OF AIRBORNE OBSERVATION COMPONENT

Airborne observations fulfill several substantial and unique roles in NASA’s integrated observing system strategy.

For research on phenomena occurring on spatial scales amenable to airborne observations, all six of the science areas discussed in this report, as well as interdisciplinary research questions, need many co-located measurements made simultaneously, within the timescales of the phenomena being studied. The shortest timescales determine the time window in which all necessary measurements must be made to answer the science questions. For atmospheric phenomena in the areas of atmospheric chemistry and physics and dynamics, the shortest timescales are often seconds to minutes; for ecological change, they are typically hours or more; and for surface dynamics, sea level rise, and water and energy cycles, they are hours to days or longer. Thus, studying atmospheric phenomena generally requires a large aircraft to carry the instrumentation and personnel to make measurements that are simultaneous on the timescale of minutes or less, while slower-evolving surface processes can often use a succession of smaller airborne platforms, each with one or a few measurements, and still make the measurements simultaneously within the timescales of the

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

phenomena. For studies of both the atmosphere and Earth’s surface, the airborne component has other unique contributions to Earth system science research. These include flexibility in configuring instrument measurement suites and rapid deployment capability to study episodic natural and anthropogenic events. Also, the airborne component can monitor the detailed progression of natural hazards and disasters with high spatial and temporal resolution that complements the more extensive but lower resolution satellite measurements. Furthermore, the unique capabilities of airborne measurements provide stringent tests, complementary to those provided by satellite measurements, for models on all scales, from local to global.

Airborne studies of Earth’s surface use remote sensing almost exclusively. The unique strengths of airborne measurements of surface properties relative to remote sensing from spaceborne measurements include increased observation flexibility in terms of geometric, temporal, and spatial scales; higher spatial resolution; precision mapping; and on-demand targeted repeat cycles from hours to months. Typically, studies use many of these unique airborne capabilities.

In situ measurements collected on board an airborne platform are typically used to study the state of atmospheric dynamics, weather, and composition as well as atmospheric processes and often their links to surface processes. The unique strengths of airborne in situ measurements include a combination of vertical profiling, spatial and temporal resolution needed for the processes being studied, measurement capability for hundreds of atmospheric constituents, detailed chemical and microphysical properties of aerosol particles, and fluxes of weather and composition variables. Airborne remote sensing measurements of atmospheric and surface properties are used to probe environments where in situ sampling is difficult, such as in thunderstorms. They also provide a larger context than in situ measurements. Sometimes remote sensing measurements are used to guide in situ measurement strategies and their post-mission interpretation.

In addition to science-driven measurement strategies, airborne observations serve several other vital roles in Earth system science research. First, satellite instruments and measurements use the airborne component of the integrated system at every stage of their development and operation. Future spaceborne sensor concepts and their data retrieval algorithms are usually first developed, tested, and refined with prototype instruments flown on aircraft. Once the satellite is operational in orbit, airborne measurements provide calibration and testing for the satellite measurements, in terms of both instrument health and algorithm improvement. Airborne capacity helps with satellite improvements through a number of strategies including underflights, vertical profiling under the satellite measurement track, and flight patterns that help relate the satellite measurement scales to the smaller scales of the atmospheric or surface phenomena that airborne instruments can measure. Second, in some cases, such as the

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

airborne NASA Operation IceBridge mission1 to monitor ice sheet changes, regular airborne measurements can fill in the data gap that occurs when one satellite ceases observation before another can be launched and become operational. Finally, airborne science plays an important role in attracting, training, and developing a diverse workforce and engaging the public.

In many cases, different aircraft and their sensors are flown to observe the same atmospheric or surface object with different measurements from different points-of-view. One example is the remote sensing of a surface object with different instruments on aircraft flying in coordination but at different altitudes or times; another is one aircraft sampling a cloud in situ while coordinated with others observing the cloud remotely. Combinations of aircraft and balloons have often been used in coordination for past airborne research. The coordinated use of several airborne platforms will likely become even more common in future Earth system science research.

2.4 A SYNOPSIS OF THE CURRENT AIRBORNE FLEET

NASA maintains an airborne fleet for Earth system research that is more extensive and diversified than the fleets of any other U.S. federal agency, the European Union’s European Facility for Airborne Research (EUFAR), or any other individual country. NASA’s aircraft and those from other agencies and countries have enabled robust and crucial contributions of airborne measurements to the integrated Earth system research strategy described previously. The following discussion provides a summary of the current aircraft being used, as well as other airborne platforms; a detailed comparison of the DC-8 with other aircraft is provided in Chapter 3.

2.4a Aircraft

The types of aircraft used for Earth system science research in the United States range from large aircraft capable of flying large payloads for long durations to the smallest UAS (Table 2.1). NASA is the only U.S. agency that has aircraft capable of flying above the upper tropical troposphere and lower stratosphere for Earth system science research (two Earth Resources 2 [ER-2] and three WB-57). NASA is also the only U.S. federal agency to operate a large former passenger jet, the DC-8. Five U.S. agencies (NASA, NSF, National Oceanic and Atmospheric Administration [NOAA], Navy Office of Naval Research [ONR], and U.S. Air Force [USAF]) have either the quad-propeller C-130 or P-3 Orion aircraft to fill the gap in capability between the DC-8 and the smaller business jets. Of the smaller aircraft, U.S. agencies and universities operate 9 modified business jets, more than 24 twin-propeller aircraft, and more than 90 single-propeller

___________________

1 See https://www.nasa.gov/mission_pages/icebridge/index.html.

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

Table 2.1 Fixed Wing Aircraft and Uncrewed Airborne Systems (UAS) in the Research Fleets of U.S. Government Agencies and Universities

Owner High-altitude jets (ER-2; WB-57) Large four-jet engine (DC-8) Large turboprop (P-3 Orion; C-130) Business jet (e.g., Gill; GV; HU-25A Guardian; Citaton; Challenger) Twin-propeller (e.g., Twin Otter; King Air B200) Single-propeller (e.g., Caravan) Medium-to-large UAS Small UAS
NASAa 5 1 2 5 4 1 2 some
NOAAb 2 1 3 many
NSFc 1 1 1
DOEd 1 1 many
ONR 1 2 several several
USAF 9
DOIe 4 76 many
USFSf 1 10 9 many
Universities several several many
U.S. agencies total 5 1 15 9 24+ 86+ 3+ many

NOTES:

a https://airbornescience.nasa.gov/aircraft.

b https://www.omao.noaa.gov/learn/aircraft-operations/aircraft.

c https://www.eol.ucar.edu/research-aircraft.

d https://www.arm.gov/capabilities/observatories/aaf/.

e Aircraft used for more than just research and resource management; OAS, 2019.

f Aircraft used for more than just research and resource management; USFS, 2018.

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

aircraft. In many cases these aircraft are used primarily for Earth system science research, whereas in others, such as for the Department of the Interior (DOI) and U.S. Forest Service (USFS), research and resource management are only two of many uses.

On occasion, commercial or private aircraft are used for Earth system science research. Typically these aircraft are single-engine and twin-engine propeller aircraft, such as a Twin Otter or a King Air B200. They are leased for a fixed period, usually a year, and can be an option if they have the ports, windows, or other fixtures for the instruments. These aircraft can have a lower cost and greater availability than NASA Airborne Science Program aircraft. However, for any NASA-funded research, NASA requires that vendors meet its Flight Program Standards for commercial aircraft concerning airworthiness and safe operation. These standards are stringent, which adds substantial time and cost to the vendor and makes it difficult for scientists to use commercial aircraft for NASA-funded Earth system science research. The committee expects that NASA will go through an exhaustive analysis of alternatives if they decide to replace the DC-8. These analyses will likely include different procurement options.

2.4b UAS

A diverse array of small UAS are already being deployed routinely for a variety of Earth system science studies, including observations of the water and energy cycles, ecological system changes, Arctic ice, and volcanic fuming. This growing use is happening because of the availability, versatility, diversity, and low infrastructure and operational costs of these smaller UAS. Their use is likely to expand substantially for some Earth system science disciplines as UAS and instrument technologies advance on several fronts: more sophisticated adaptive and automated flight control; greater UAS payload capacity; smaller, lighter, more power efficient, and more automated instrumentation; and a growing diversity of designs to meet specific needs. Among the new UAS under development are UAS that are powered by solar cells and batteries and can carry small payloads, with the objective of flying to specific locations and then hovering for days to weeks at a time.

The small UAS can be deployed from ships and large aircraft for targeted observations that are often otherwise difficult to obtain, especially in extreme conditions of high-impact weather. For example, most recently, NOAA has deployed UAS from the P-3 aircraft to collect data in the PBL in the eye and eyewall regions of hurricanes (Cione et al., 2020). The Defense Advanced Research Projects Agency Gremlins program successfully flew its X-61A Gremlins Air Vehicle for the first time in November 2019, which is currently under consideration for future Earth system science applications.

For medium-to-large UAS, the use for Earth system science research is modest but growing compared to piloted aircraft for two main reasons. First, the cost per flight-hour is very high. Second, the regions, vertical range, and circumstances under which these UAS can operate are much more limited than for piloted aircraft. In addition, for

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

atmospheric chemistry research, the payload size and power requirements of in situ instruments can be insufficient to achieve science goals. However, for remote sensing of Earth surface with one instrument, these UAS and their long flight duration can be useful, although at a high cost.

The greatest challenge for the use of all UAS is the variable and evolving set of national and international rules and regulations for their use. The civil aviation authorities for different countries have developed rules and regulations that allow for varying levels of risk to people and property from UAS operations. The United States, for example, has stringent safety requirements for UAS operations to ensure that failure of a UAS or subsystem of the UAS will not endanger people or property on the ground or in the air. As of April 2021, the flight of UAS outside of the visual line of sight of the pilot in command in the National Airspace System is prohibited except for a few, very limited cases. This limits UAS use for long-range scientific missions. However, as UAS safety technology develops and is able to reduce the risk of an operation, the Federal Aviation Administration incorporates that technology into its risk analyses and develops policies and procedures that will allow more operational types to occur. For example, on-UAS technology that can spot another aircraft in the airspace and autonomously avoid it is being developed and could decrease the risk posed by long-range UAS operations. As UAS technology matures and regulators, operators, and standards bodies develop the technologies, standards, and rules for ensuring aviation safety, UAS should become more widely used for Earth science missions.

2.4c Balloons

Small helium-filled balloons are routinely launched synoptically across the globe for upper atmospheric soundings of atmospheric pressure, temperature, and relative humidity. They are also used for monitoring and studying ozone (World Meteorological Organization ozonesondes), episodic observations of aerosol particles (Hofmann et al., 1989; Vernier et al., 2018), and methane and carbon dioxide from “AirCores” (Karion et al., 2010). In all these cases, the goal is to get an altitude sounding at individual locations. While these soundings are critical for weather predictions, detecting and understanding climate trends, and studying global ozone, the limitations on payload weight inhibit a substantially wider use of small balloons for Earth system science research.

Large helium-filled balloons capable of carrying as much as 2,000-kg payloads were heavily used for measuring atmospheric trace gases from the upper troposphere to the middle stratosphere in the 1970s to the early 2000s but have not been used much since (NRC, 2010). The advantage of large balloons is that they are the only way to sample the stratosphere above about 20 km with fine vertical resolution. The disadvantages are that they can take weeks to launch, the number of possible launch sites is limited, and their flight path is dictated by the wind.

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

Within the past few decades, there have been new developments in large balloon technology. Superpressure balloons have been developed for long-duration flights lasting a few months. These balloons have been deployed to circumnavigate Antarctica and, with the ability to carry 100 kg payloads, could be used for in situ stratospheric ozone measurements or remote sensing of ice sheets. Another concept currently being discussed is the “Stratocruiser” reel-down system that would be able to lower and raise the payload over a few kilometers to do vertical in situ sampling in the stratosphere. These balloons are not steerable and thus their payload instruments can sample only where the winds take them.

Stratospheric balloons are currently being developed to sustain station-keeping for days to weeks. Although they are propelled by the wind, they can, under some conditions, navigate and station-keep by changing altitudes in winds that vary with altitude. Currently this technology has been developed for payloads less than about 100 kg and a few hundred watts of power and is being deployed for a variety of government and private industry purposes by at least one company (World View Enterprises). With their combination of better spatial resolution than satellites and longer duration than aircraft, these steerable stratospheric balloons may have some remote sensing applications. Although stratospheric balloons have potential for long-duration remote sensing at a single location or in a circumpolar pattern, aircraft have much greater capability for remote sensing over the wide range of wind conditions, global locations, flight patterns, and targeting times that are necessary for the broad range of remote sensing needs for Earth system science research.

2.4d Aircraft from Other Countries

Governmental and other organizations abroad are also invested in airborne fleets as part of their own research strategy and their contribution to international research. The largest of these is EUFAR in Europe, which brings together several large European airborne research facilities and a number of small operators. The EUFAR member organizations provide 12 aircraft (3 modified business jets, 5 twin-propeller aircraft, and 4 single-propeller aircraft) directly through EUFAR, while other mostly European organizations provide 33 additional aircraft (mostly single-propeller or twin-propeller aircraft).2 For stratospheric research, the European Geophysica serves a similar role for Europe that the NASA ER-2 does for the United States. Of the aircraft used for Earth system science research, the largest in the EUFAR fleet is the United Kingdom National Environment Research Council BAe-146, a four-engine regional jet, which compared to the DC-8 has 85 percent of the payload weight capacity and altitude range, 60 percent of the cabin volume, and 20 percent of the range and duration. Canada, South Korea,

___________________

2 See https://www.eufar.net/.

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

China, and Japan maintain smaller airborne fleets for Earth system science research, consisting mainly of business jets and single-propeller or twin-propeller aircraft.

While funding agencies from the United States and other countries tend to fund research using aircraft they control, in many instances, they have worked together to achieve research goals. A recent example of a U.S.-European collaboration was the 2012 Deep Convective Clouds and Chemistry (DC3) study in the central United States, in which the DC-8, the NSF Gulfstream V (GV), and the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt) Falcon aircraft all flew in the anvils of active deep convection (Barth et al., 2015). Another example is the coordination between the U.S. Department of Energy Gulfstream-159 (G1) aircraft and the German High Altitude and Long-range Aircraft over the Amazon rainforest that was sometimes impacted by air pollution from the tropical megacity, Manaus, Brazil (Mei et al., 2020). A third example is the NASA Airborne Visible/Infrared Imaging Spectrometer Next Generation (AVIRIS-NG) being mounted on the Indian Space Research Organization’s King Air B200 for recent surface studies in India.

2.4e Airborne Research Using Many Platforms

Many aircraft and balloons have often been used in coordination for past airborne research. In many cases, different aircraft and their sensors are flown to observe the same atmospheric or surface object with different measurements from different points of view. One example is the remote sensing of a surface object with different instruments on aircraft flying in coordination but at different altitudes or times; another is one aircraft sampling a cloud in situ while coordinated with others observing the cloud remotely. These other airborne platforms have included not only other piloted aircraft but also UAS and balloons.

Often NASA contributes its airborne platforms, including those that are unique such as the DC-8, to collaborative efforts that include airborne platforms from other U.S. agencies, other countries, universities, and private organizations. Satellites continue to develop capability of multivariable measurements, growing the needs for calibration and validation (Cal-Val) using several airborne platforms in the United States and internationally. The joint European Space Agency-NASA Aeolus Cal-Val efforts demonstrate a highly collaborative activity including several Falcon and smaller aircraft from other countries, along with the DC-8 because of its capability of carrying several radars and lidars. Airborne research using multiple platforms from multiple organizations will become even more essential as Earth system science questions become more interdisciplinary and more complex.

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

2.5 EVOLUTION OF INSTRUMENTATION FOR AIRBORNE SCIENCE

Hundreds of different instruments have been used on aircraft for Earth system science research in the past several decades, almost half of which have flown on the DC-8. Descriptions for many of these instruments are in the NASA Airborne Science Instrument Database.3 Most of these instruments were funded by federal agency research programs, such as NASA’s Instrument Incubator Program (IIP). Many were developed in government, private, and university laboratories and have been used in NASA-sponsored research primarily by the scientists who developed them. However, NASA also has facility instruments that are currently supported by NASA and provided for use to the wider science community through a flight request process.

2.5a NASA Facility Instruments

NASA facility instruments are generally large remote sensing instruments, including cameras, spectrometers, interferometers, a lidar, and a radar (Table 2.2). Some are similar to spaceborne instruments, such as the enhanced Moderate Resolution Imaging Spectroradiometer (MODIS) airborne simulator (eMAS) and MODIS/Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Airborne Simulator (MASTER). Except for eMAS, the current nine facility instruments can be adapted to fly on several different aircraft, although often new instrument mounting hardware must be designed, approved, and built for each aircraft, at a sometimes considerable cost, before that instrument can be used. These instruments are used to study the properties of land, ocean, ice, water, and vegetation and their changes with time.

Table 2.2 Current NASA Facility Instruments and Aircraft on Which They Fly

Title Aircraft Type Mass (kg)a Volume Measurements
Airborne Visible/Infrared Imaging Spectrometer—Classic (AVIRIS) ER-2, Proteus, Twin Otter, WB-57 Imaging spectrometer (upwelling spectral radiance) measured across 224 bands (from blue visible through shortwave infrared, between 400 350 (772 lb) 1.5 × 1.2 × 1 m

(59″ × 47″ × 39″)
Imagery applied to studies across fields of ecology, oceanography, environmental science, snow hydrology, geology, agriculture, limnology volcanology, soil and land management,

___________________

3 See https://airbornescience.nasa.gov/instrument/all.

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
and 2,500 nm) across a 677-pixel swath, with an IFOV calibrated to within 0.2 mrad water vapor, and aerosols
Applanix Position and Orientation System (POS AV) DC-8, B200, Caravan, Cessna, WB-57 Navigation recorder and software for direct georeferencing; allows precise image georectification 7 (15 lb) 510 PCS (0.25 × 0.16 × 0.08 m; 10″ × 6.2″ × 3.2″); IMU (0.1 × 0.1 × 0.09 m; 3.75″ × 3.75″ × 3.35″); PCS (0.25 × 0.16 × 0.08 m; 10″ × 6.2″ × 3.2″); IMU (0.17 × 0.17 × 0.16 m; 6.5″ × 6.5″ × 6.4″) Aircraft position
Digital Mapping System DC-8, P-3 Orion, C-130, HU-25A Guardian, GV Natural color and panchromatic imagery using a Canon/Zeiss camera with 21 megapixels measured with IMU/GPS 7 (15 lb) 0.2 × 0.2 × 0.2 m

(6″ × 6″ × 6″)
Imagery, wide applications for many environmental studies
Enhanced MODIS Airborn Simulator (eMAS) ER-2 38-band multiband spectrometer, with bands from 0.45 µm blue visible through 14 µm thermal infrared 150 (330 lb) Scan head (0.6 × 0.46 × 0.5 m; 23.5″ × 18″ × 19.5″); Digitizer (0.55 × 0.2 × 0.3 m; 21.75″ × 7.5″ × 11″); Power Dist. (0.55 × 0.2 × 0.3 m; 21.75″ × 7.5″ × 11″); Data system (0.16 × 0.1 × 0.3 m; 6.25″ × 4″ × 11″) Imagery, wide applications for many environmental studies
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Title Aircraft Type Mass (kg)a Volume Measurements
Land, Vegetation, and Ice Sensor (LVIS) DC-8, B200, Gulfstream V, C-130, P-3B, HU-25C Guardian Falcon Wide-swath imaging laser altimeter; a 1,024-nm laser records pulses, and all returns are captured from three detectors; flown with high-resolution digital camera. Depending on flight altitude, can collect data at footprints from a few meters to about 25 m, and swath size ranges from about 2 km to about 4 km 79 (175 lb) 0.53 × 0.53 × 0.62 m (20.75″ × 20.75″ × 24.55″) Three-dimensional structure of vegetation, topography, and ice

Imagery (from digital camera or from rasterized pulse clouds)

Surface topography with decimeter accuracy
MODIS/ASTER Airborne Simulator (MASTER) B200, DC-8, ER-2, WB-57, P-3 Orion 50-Band spectrometer covering VNIR, SWIR, MWIR, TIR imagery, 25 bands in solar spectrum and 25 in thermal infrared 143 (315 lb) Scan head (0.6 × 0.46 × 0.5 m; 24″ × 18.25″ × 20″) Digitizer (0.69 × 0.48 × 0.3 m; 27″ × 19″ × 11″) Imagery, wide applications for many environmental studies, such as for evapotranspiration
National Airborne Sounder Testbed – Interferometer (NAST-I) ER-2, Proteus, WB-57 Michelson interferometer sounding system measuring temperature and relative humidity, with high spectral resolution 100 (221 lb) Canister (1.3 × 0.77 × 0.71 m; 52.5″ × 30.25″ × 28″); Controller (0.48 × 0.33 × 0.13 m; 19″ × 13″ × 5.25″); Heater control box (0.25 Temperature, relative humidity
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
(0.25 cm-1) for 3.5- to 16-µm high spatial resolution (0.13-km linear resolution per km of fight altitude at nadir) × 0.48 × 0.09 m; 10″ × 19″ × 3.5″)

Pilot interface (0.48 × 0.18 × 0.09 m; 19″ × 7″ × 3.5″); Monitor/keyboar d
Airborne Visible/Infrared Imaging Spectrometer—Ne×t Generation (AVIRIS-NG) ER-2, Twin Otter (DHC-6), King Air B200 Imaging spectrometer (upwelling spectral irradiance on 426 bands between 380 and 2,510 nm) 250 (551 lb) 1.0 × 0.75 × 0.75 m (39.4″ × 29.5″ × 29.5″) Imagery, wide applications for many environmental studies
Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) Gulfstream III Radar (polarimetric L-band or P-× band or Ka-band synthetic aperture radar) acquiring repeat track SAR data for differential interferometric measurements 408-454 (900-1,000 lb) ~0.6-m diameter × 3.35-m length (~24″ diameter × 132″ length) Imagery

NOTE: DHC = De Havilland Canada, GPS= global positioning system, IFOV = instantaneous field of view, IMU = Inertial measurement unit, MWIR = medium wavelength infrared, PCS = instrument control system, SWIR = short-wave infrared, TIR = thermal infrared, VNIR = visible and near-infrared.

a Instrument mass and volume information provided by NASA.

2.5b Other Instrumentation and Some Common Applications

Of the hundreds of instruments that are not NASA facility instruments, some are still frequently used while others are not. The group of remote sensing instruments currently in use include lidars, radars, passive spectral sensors in wavelength ranges from the ultraviolet to the microwave, and radiometers for measurements of both surface and atmospheric variables and processes.

For research involving ecological change, a few notable non-facility instruments are frequently used. One is the Hyperspectral Thermal Emissions Spectrometer, which maps

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

256 spectral channels between 7.5 and 12 μm at 5- to 50-m spatial resolution.4 Another is the compact, lightweight Portable Remote Imaging SpectroMeter, which can measure submeter-size ocean color, chlorophyll-a, other marine pigments, and radiance using a visible spectrometer (248 bands from 350 to 1,053 nm) and two shortwave infrared bands at 1240 nm and 1640 nm (Mouroulis et al., 2014).

For atmospheric dynamics research, remote sensing instruments are being combined on a single aircraft to achieve science goals. For instance, the DC-8 will be used to fly three remote sensing instruments simultaneously for the upcoming Convective Processes Experiment–Aerosols and Winds study. This project will investigate interactions between Saharan dust over the Atlantic Ocean and convection leading to the formation of tropical storms. The first instrument is the Doppler Aerosol WiNd lidar, which provides vertical profiles of zonal and meridional horizontal wind below the aircraft at a resolution of about 60 m (Kavaya et al., 2014). These profiles are derived from measurements of the backscatter from a pulsed near-infrared laser beam that is scanned over a 30o arc below the aircraft. The second instrument is the Airborne Third Generation Precipitation Radar, which is a three-frequency Doppler dual-polarization radar that measures radar reflectivity and Doppler velocity in a track below the aircraft (Durden and Perkovic-Martin, 2017). The third is the High Altitude Monolithic Microwave integrated Circuit Sounding Radiometer, which is a multiwavelength channel, multimicrowave band that measures three-dimensional distributions of temperature, water vapor, and cloud liquid water.5

For atmospheric chemistry research, a number of in situ and a few remote sensing instruments measure some of the following: environmental physical state variables; a number of the hundreds of trace gases of interest, from small molecules such as the hydroxyl radical, to large organic molecules; ice and liquid cloud drop and aerosol particle properties such as size, composition, optical properties, and other particle characteristics. An example of a remote sensing instrument is the High Spectral Resolution Lidar that measures aerosols (Knobelspiesse et al., 2011). For in situ measurements, smaller molecules are increasingly being measured with laser absorption or resonance fluorescence techniques while large molecules are being measured with mass spectrometry. Because each in situ instrument can measure only certain types of gases or particle properties, a suite of in situ instruments is needed to gain a complete picture of the atmosphere’s physical state and composition.

2.5c Deployable Instruments

Sensors deployed from aircraft are another class of evolving instruments, a concept that uses aircraft effectively to do targeted sampling that could not be accomplished any

___________________

4 See https://hytes.jpl.nasa.gov/.

5 See https://airbornescience.nasa.gov/instrument/HAMSR.

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

other way. These include dropsondes that measure temperature, pressure, dewpoint temperature, and wind speed and direction, which are the same quantities measured by radiosondes in the global upper air network, but dropsondes can be targeted for specific locations such as in tropical cyclones. Other instruments deployed from aircraft include Airborne eXpendable Bathythermographs and air-launched Argo floats, which, when dropped into the ocean, measure salinity, temperature, and pressure within the water column. A new development is UAS that can be dropped from aircraft and then either be directed or fly autonomously to measure specific regions of interest nearby, such as near surface and PBL of extreme high-wind conditions in hurricanes (Cione et al., 2020).

2.5d Miniaturization

The size, weight, and power requirements of airborne instruments, both remote sensing and in situ, have been and continue to be important factors in driving the need for large airborne platforms. Aircraft payload limitations have often forced compromises on achieving proposed measurement goals or have likely stifled the imagining of new multi-instrument strategies that could significantly advance Earth system science. Also, the size, weight, and power requirements dictate the type of aircraft that can be used to accomplish the science. Thus, finding ways to miniaturize instruments—that is, reduce their size, weight, and power requirements—brings significant benefits to Earth system science research. In some cases, miniaturization means upgrading components and repackaging an existing instrument, while in others, it means building a new instrument based on advanced technologies and a different measurement concept altogether.

One example of miniaturization of a NASA facility instrument is synthetic aperture radar. The Airborne Synthetic Aperture Radar (AIRSAR, 1988-2004) was an all-weather imaging radar that was used extensively for Earth surface and ecology studies—from glacier movement, snow mapping, and seismic activity to vegetation change to land subsidence and groundwater use. It required the DC-8 because it weighed 1,720 kg, drew 10 kW of power, and consisted of 13 electronics racks and several large antennas that covered a large area of the aircraft's outer surface (see more about AIRSAR in Section 3.2). A miniaturized version of this instrument, the Uninhabited Aerial Vehicle Synthetic Aperture Radar, was developed using advanced technologies, has twice the spatial resolution of AIRSAR, and is capable of precision autopilot. It weighs 450 kg and fits into a 3-m-long pod, and is routinely used on much smaller aircraft than the DC-8.

Among in situ instruments, an example of miniaturization is instruments using fiber lasers, an advancement in laser technology that is being driven by telecommunications and industrial applications. These small, energy-efficient lasers are being used on aircraft to measure important atmospheric constituents, such as formaldehyde or nitric oxide, by laser-induced fluorescence. Once these instruments are thoroughly tested against the large, heavier legacy instruments, their use will save substantial space and

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×

weight for future missions, enabling use on smaller aircraft or the addition of other measurements that otherwise would not fit on the aircraft.

The cost of instrument miniaturization, typically funded by federal agency research programs such as NASA’s IIP, depends on advances in design, materials, and technology of the instrument components. If these advances are specifically for an instrument used in Earth system science research, then the costs can be high. However, if these advances are developed by companies for commercial use, then the costs can be lower. Most miniaturization of Earth system science instrumentation uses some combination of instrument-specific and commercial advances and thus has a wide range of costs.

Technological advances will likely continue to enable instruments to become smaller, lighter, more energy-efficient, more autonomous, and more affordable for airborne Earth system science observations. Improvements are coming from using modularized subsystem architecture (“plug and play”) and designing architectures that allow increased flexibility and adaptability to multiple measurement objectives, complementing active/passive measurement techniques (radar/radiometer and lidar/spectrometer). Size, mass, and power reduction will also come from mass-producible miniaturized key instrument components or subsystems, rapidly emerging technologies such as photonic integrated circuits, system-on-chip solutions, free-form optics, room-temperature detectors, and other compact electronic and optical architectures.

The historical evolution of airborne measurement technologies provides some guidance for NASA’s Earth system science aircraft future needs. First, instruments developed for new measurements have generally been larger and more conservatively designed and often need operators on board, requiring a larger aircraft. However, over time, experience with an instrument’s airborne performance and advances in technology have often enabled miniaturization of the instrument or its components (e.g., AVIRIS and AVIRIS-Next Generation [AVIRIS-NG]; see Table 2.2). This trend from the instrument being initially larger and then miniaturized is likely to continue for a substantial number of new instruments even with technological advances. Second, some instruments may be difficult to shrink and still retain the necessary sensitivity, spectral resolution, or sampling capabilities, such as mass spectrometers for in situ gas or particle measurements and whole-air samplers. Third, as instruments become smaller, lighter, more energy efficient, and more autonomous, clever new measurement strategies will likely arise that require larger suites of these instruments measuring more variables in order to meet Earth system science research goals, particularly for emerging interdisciplinary research. For these reasons, technological advancements in instrumentation will not necessarily alter the composition of the NASA airborne fleet that is needed to accomplish Earth system science research goals well into the future.

Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 17
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 18
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 19
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 20
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 21
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 22
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 23
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 24
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 25
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 26
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 27
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 28
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 29
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 30
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 31
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 32
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 33
Suggested Citation:"2 Setting the Stage: The Role of Airborne Platforms in Earth System Science." National Academies of Sciences, Engineering, and Medicine. 2021. Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft. Washington, DC: The National Academies Press. doi: 10.17226/26079.
×
Page 34
Next: 3 The DC-8 Airborne Research Platform »
Airborne Platforms to Advance NASA Earth System Science Priorities: Assessing the Future Need for a Large Aircraft Get This Book
×
Buy Paperback | $65.00 Buy Ebook | $54.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

The National Aeronautics and Space Administration (NASA) and other U.S. science research agencies operate a fleet of research aircraft and other airborne platforms that offer diverse capabilities. To inform NASA's future investments in airborne platforms, this study examines whether a large aircraft that would replace the current NASA DC-8 is needed to address Earth system science questions, and the role of other airborne platforms for achieving future Earth system science research goals.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!