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J
Environmental Parameters
Does EOS collect the erzvironmer'tal parameters that are reflected in
the USGCRP research priority framework and related policy issues
described in `'Our Changing Planet',?
To answer this question, we first considered the overall USGCRP
research priority framework, which states three integrating priorities: (1)
documentation of Earth system change with observational programs and
data management systems; (2) improvement of understanding through
focused studies of the controlling physical and biogeochemical processes;
and (3) development of integrated conceptual and predictive models. EOS
is designed to contribute primarily to items (1) and (2~; EOS data will also
be used in the development, validation, and ultimate applications in (3~.
The relative emphasis EOS places on process studies and monitoring global
change is one that will evolve. At present, EOS is intended to contribute
to both, with a stronger focus on process studies. In the long run, it will
become a major system for monitoring global change. The changing nature
of these roles must be recognized and flexibility must be built into the
system so that EOS can adapt.
In summary, we find that EOS is being designed to measure environ-
mental parameters from space that reflect the USGCRP framework and
that will allow researchers to make major contributions to global change
research. However, there are general strategy issues that need further
development, and we have also identified some specific issues involving
instruments.
34
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35
THE MEASUREMENT SYSTEM FOR GLOBAL CHANGE
It is generally agreed throughout the international scientific commu-
nity associated with global change that adequate documentation of envi-
ronmental change on Earth requires a combination of space-based and in
situ measurements. "In situ" in this sense means in the atmosphere, on the
surface of the Earth, and on and in the oceans.
The need for this combination of space- and Earth-based measure-
ments is well-documented in reports from the NRC and from NASA The
most recent NRC reports come from the Committee on Science, Engi-
neering, and Public Policy (Report of the Research Beefing Panel on Remote
Sensing of the Earth, 1985~; from the Committee on Earth Sciences and the
Ask Group on Earth Sciences of the Space Studies Board (A Strategy for
Earth Science from Space in the 1980s and 1990s, Parts I and II, 1982, 1985;
Mission to Planet Earth, 1988~. The most recent NASA report addressing
the full set of science issues, with recommendations for both NASA and
NOAA, comes from the Earth System Science Committee Earth System
Science: A Closer Mew, 1988~. The NRC and NASA reports are the work
of a representative and broad segment of the U.S. scientific community,
and we believe that those reports accurately reflect broadly held views.
The two types of measurements complement each other. Space-based
measurements can provide a global and synoptic view of Earth's envi-
ronmental parameters and processes no. available any other way. In situ
measurements document those processes not accessible from space, such as
deep ocean currents. Cloud cover prevents many important measurements
from being made from space; for a number of process studies, observations
are needed within and under clouds. Moreover, the vertical and horizontal
resolution and accuracy of certain variables that can be obtained from
space are inadequate for certain process studies of importance to global
change. Thus there will always be a need for in situ measurements as part
of a global change observing system. The combination of space- and Earth-
based measurements is essential; neither can provide a complete picture
on its own.
There are important variables, such as chemical constituents and other
internal variables of the ocean, that cannot be measured at all from space;
other variables, such as cloud droplet distribution and turbulence, cannot
currently be measured well from space.
The requirement for complementary measurements has been met for
several near-term satellite systems by the development of large coordinated
in situ programs. For example, the World Ocean Circulation Experiment
(WOCE) was designed to carry out global in situ measurements of ocean
circulation at the same time that altimeters and scatterometers will be flown
in space on the European Space Agency's (ESA) ERS-1, the U.S./French
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TOPEX/Poseidon spacecraft, and the Japanese ADEOS satellite. The first
pilot studies of the hydrological cycle under the Global Energy and Water
Cycle Experiment (GEWEX) are planned to be carried out at the same
time as the flight of the proposed Topical Rainfall Measurement Mission
(TRMM). The major studies of GEWEX are proposed to be carried out
at the same time as the EOS program.
However, an overall strategy for in situ measurements in the time
frame of EOS has not been developed. Because of the long lead time
necessary for such planning, we conclude that the agencies involved in
the USGCRP should begin to develop the plan soon. Without a carefully
planned in situ program, including international participation, much of the
USGCRP will not be able to take full benefit of EOS and other space-based
measurements.
EOS IN THE CONTEXT OF OTHER SPACE MISSIONS
While EOS will provide an essential part of the total set of observa-
tions required for the U.S. Global Change Research Program, not all the
environmental parameters required for understanding global change that
can be measured from space can be measured by the EOS spacecraft.
Therefore, EOS must be viewed in the context of other space-based
measurement systems of both the U.S. and other nations participating in
global change research that will fly either before or concurrently with EOS.
Some parameters must be measured by space-borne instruments on other
satellites and in other orbits. The full set of space-based observations that
will contribute to improved understanding of global change are expected
lo be made by EOS together with numerous other spacecraft. These
include NASA research programs such as UARS and TOPEX/Poseidon,
the Earth Probes series, and instruments on Shuttle flights, as well as
NOAA and DOD operational satellites, and operational and research
satellites launched by other nations.
An overall international observational strategy that includes all these
research and operational satellites and instruments has been discussed, but
not yet developed. (See, for example, IGBP Needs for Remote Sensing u:
the 1990s and Beyond, a forthcoming report from the Special Committee
for the IGBP.) There is a sense of the missions that the respective na-
tions or agencies would like to fly, but there are also uncertainties. An
international strategy would be useful for ensuring the continuity of ob-
se~vations (see Chapter 7 on Continuity and Reliability) and the efficient
use of resources. Because NASA has taken the lead in developing the
remote-sensing technology for global change research, the agency, working
within the CEES, should also take the lead in developing an international
strategy for space-borne measurements of global change.
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37
EOS AND THE USGCRP
In order to assess the contributions of EOS to the measurements of
environmental parameters necessary for documenting global change, it must
be recognized that EOS is only part of the space-based system required
and that the space-based observations are only part of the total space-based
and in situ measurements required.
EOS is currently designed to provide a 15-year series of measurements
from a sun-synchronous polar orbit with a set of highly developed instru-
ments. Such instruments will have higher spectral resolution by orders of
magnitude than any available today or likely to be available in the near
future. In addition, EOS instrumentation will include advanced versions
of existing operational instruments for continuity of measurements. By
flying several of these instruments simultaneously, NASA plans to achieve
. .
a major Improvement in the description of global physical and biogeochem-
ical phenomena. The global change research community looks to EOS to
provide new technology for measuring parameters not adequately studied
today, as well as to continue the measurements of parameters that are
reasonably well understood. The objective is for EOS to provide the user
community (science, industry, policy) with the first comprehensive long-
term measurement and data system specifically aimed at global change
issues.
The proposal for a 15-year series of satellites focused on study of the
Earth raises issues of programmatic strategy. EOS has a dual character,
combining typical research missions with others that have more of the
characteristics of operational monitoring missions, such as those flown by
NOAA and DOD. Research missions are typically strongly dependent on
a few individuals who devote portions of their careers to them, whereas
operational missions are designed to deliver data to other users on a
reliable and routine basis. Because all EOS data are intended to be widely
shared, a more operational strategy is required-even for the pure research
objectives. Furthermore, the general strategy and the specific instrument
details and algorithms should be fully documented.
During the development of the EOS concept, NASA formed a Science
Steering Committee that produced the volume entitled From Pattern tO
Process: The Strategy of the Earth Observing System. That report proposed
the Implementation, individual measurements, and synergistic measurement
strategies for EOS. In the interim, however, much has changed. New
instrument concepts have been developed; others have been discarded.
A competitive selection process has been conducted naming instrument
investigators and teams to perform interdisciplinary studies. A budget
profile now defines a funding envelope for investigators, instruments, and
spacecraft.
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38
It is now vital to begin the process of updating the earlier work of the
Science Steering Committee to develop the successor to From Pattern to
Process. As indicated earlier, the successor should detail the observational
strategy for space-based observations and the ancillary in situ and ground-
based measurements that accompany them. The required strategy would
go beyond From Pattern to Process, however, in that it should include in
situ measurements. Consequently, while NASA should participate in its
preparation, responsibility for its development should fall to the CEES.
The GEWEX program provides an example of a coordinated inter-
national observational strategy to support research of the type envisioned.
GEWEX relies first on limited in situ and satellite (TRMM) observations
for a pilot study to be followed by an extensive ground-based measurement
program complemented by EOS data.
The observational strategy should indicate how each observing system
and measurement contributes to the overall scientific objectives of the
USGCRP. In particular, it should show how each measurement, with its
associated accuracy and resolution in space and time, will contribute the
desired end product of global or regional data sets that will advance our
understanding and predictive capability of the Earth system. Perhaps most
important, it should allow for the evolution of observational goals and
technology and should be updated from time to time. We can refer to this
documentation as providing "traceability".
The new study must scrupulously state the objectives and rationale for
the deployment of the series of instrument suites, and provide with refer-
eed journal care the traceability to the detailed assumptions and analyses
upon which the objectives and rationale are based. As the study evolves
and changes, it is important that the strategy be comprehensive and clear.
Changes stemming from either scientific, technological, or financial recon-
sideration of the mission must be understood and thoroughly documented.
The simplest statement of the objective of the EOS program is that
it will advance mankind's understanding of the continuing evolution of the
planet. Unlike most scientific investigations, the value of EOS will lie in
itS aggregate accomplishment, rather than in the important but individual
achievements of the respective investigator teams. Thus documentation that
aids and guides the aggregate accomplishment, to which newcomers can also
refer, is vital. Therefore, we recommend that NASA initiate immediately
the development of a documentation plan, and quickly thereafter the
documentation itself that will be required in this multidecadal program.
Summary Recommendations
In view of the fact that EOS is a 15-year program, a fully- documented
strategy and specification of instruments must be developed and updated
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as required. This is the only way that EOS can serve as an intermediate
step between the research missions of the past and the operational systems
of the future.
As indicated earlier, the set of instruments under consideration for
flight appears to be capable of providing a comprehensive set of mea-
surements of high priority environmental parameters. The complete set
of measurements eventually to be made from EOS spacecraft will depend
on the successful development of the respective instruments, as well as on
other factors. In the sections below, we briefly summarize the contribution
of EOS measurements to the objectives of the USGCRP. It should be
noted at the outset that specific agency planning will not necessarily have
the same framework as that developed by the USGCRP, but the specific
elements of agency programs should be relevant to the overall framework.
Each of the specific elements of the EOS scientific plan contributes to one
or more of the elements of the USGCRP.
Because EOS has been proposed as a major contribution to the US-
GCRP, the overall strategy for the program and the selection of instruments
and orbit should be optimized on the basis of USGCRP priorities. Review
processes should be set up to ensure that this close connection is made and
maintained.
A clear strategy and process should be established by which instruments
are selected. This strategy would determine the measurements to be made
and, therefore, the individual and aggregate research to be done. The
specific research objectives, and possibly even the general goals, of the
USGCRP will change as more is learned about the subject. The technology
of remote sensing is also likely to change over the life of the program.
Although continuity of specific data sets will be an important consideration,
it may be desirable to alter the instruments or the platforms, or both, at
some time in the future. Currently, the program contains no process that
would enable it to evolve in response to new scientific understanding or
technological developments.
CONTRIBUTIONS TO SPECIFIC USGCRP SCIENCE PRIORITIES
Because we have been asked to consider the contribution of EOS to
the USGCRP, we use the set of priorities listed in the FY 1991 version
of Our Changing Planet. The USCGRP framework provides for specific
science priorities in seven interdisciplinary areas: (1) climate and hydrologic
systems; (2) biogeochemical dynamics; (3) ecological systems and dynamics;
(4) Earth system history; (5) human interactions with the Earth system; (6)
solid Earth processes; and (7) solar influences. NASA has described ills
program in slightly different terms.
As currently planned, EOS data are expected to contribute in a major
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way to areas (1), (2), (3), and (6); less extensive contributions are expected
to be made to areas (4), (5), and (7). The specific contributions are
discussed in the sections below. In each section we quote the policy-
relevant questions as noted in the FY 1991 version of Our Changing Planet,
and then summarize current plans and proposals for space missions to
address them, including the proposed EOS contributions. In the discussion
of particular instruments, it should be noted that in some cases the process
of selecting between competing instruments is still under way. In every case,
we emphasize that we refer to the generic class of instrument represented
by the particular example cited; naming a specific instrument is not to be
taken as an endorsement of that instrument over competing instruments
for flight on EOS.
Climate and Hydrologic Systems
1. What is the role of clouds in the Earth's radiation and heat
budgets?
Near-term Plans
The ongoing programs for monitoring the Earth's radiation budget, the
Earth Radiation Budget Experiment (ERBE) and the International Satellite
Cloud Climatology Program (ISCCP), if continued until the launch of EOS,
will provide continuity for this important parameter, which is one of the
principal diagnostics of the "greenhouse" effect. ~ monitor the Earth's
radiation budget properly, daily global data from two polar orbits (a.m. and
p.m.) and a mid-latitude inclined orbit (50 to 60 degrees) are required.
It should be noted that a joint French/Soviet radiation experiment,
the Scanner for Radiative Budget (SCARAB), is scheduled to be flown in
1991. This experiment will help to provide a follow-on to ERBE in the
early 1990s. Unless another Earth radiation budget measurement mission
is flown, however, there will be a several year gap in such data between the
end of the SCARAB mission and the beginning of EOS.
EOS Plans
The EOS instrumentation makes a major contribution to answering the
question about the role of clouds in climate. The high degree of temporal
and spatial variability of cloud-atmosphere radiation interactions and fluxes
of heat and energy at the surface must be measured accurately. The
EOS instruments promise to provide accurate atmospheric temperature
profiles with the Atmospheric Infrared Sounder (AIRS) and the Advanced
Microwave Sounding Unit (AMSU). The current atmospheric temperature
and water vapor profiles provided by the operational HIRS/AMSU system
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41
constitute valuable data where other measurements are sparse, as in the
southern hemisphere. To date, however,- they have proved to be of less
utility where dense networks of in situ observations exist. The instruments
proposed for EOS promise higher spatial and spectral resolution as well as
improved accuracy.
The Clouds and Earth's Radiant Energy Systems (CERES) radiome-
ter is designed to determine broadband shortwave and longwave top-
of-atmosphere radiances. The High-Resolution Microwave Spectrometer
Sounder (HIMSS) would establish water content of clouds over the ocean.
The Moderate Resolution Imaging Spectrometer (MODIS) in its nadir
looking mode is intended to provide spectral information needed for de-
termining physical cloud properties and cloud height. The Earth Observ-
ing Scanning Polarimeter (EOSP) would determine aerosol composition.
The Multiangle Imaging Spectro-Radiometer (MISR) promises, through its
multi-angle viewing capability, to provide the bulk radiative properties of
aerosols in the shortwave spectral region.
The current plan for EOS has adequate instrumentation for monitoring
the Earth's radiation budget from a p.m. polar orbit. Data from an -a.m.
polar orbit could be provided by the European Polar Orbiting Platform
(EPOP) or the NOAA polar orbiting satellite series. An inclined-orbit
instrument is planned for the Space Station, in a tropical orbit. At 28
degrees, the inclination of the Space Station's orbit is too low to complement
coverage in the high latitude regions. Moreover, uncertainties in the time
of the Space Station launch may reduce coverage unacceptably.
EOS includes plans to monitor solar output with the Solar Stellar
Irradiance Comparison Experiment (SOLSTICE) and the Active Cavity
Radiometer Irradiance Monitor (ACRIM). SOLSTICE would provide pre-
cise daily measurements of the full disk solar ultraviolet irradiance; ACRIM
would monitor the variability of total solar irradiance with state-of-the-art
. .
accuracy ant precision.
Finding
A gap in measurements of the Earth's radiation budget will occur in
the mid-199Qs if no additional mission is proposed. A follow-on to the
SCARAB experiment at an adequately inclined orbit will be needed. Such
a mission would be suitable for the Earth Probes series.
2. How do the oceans interact with the atmosphere in the storage,
transport, and uptake of heat?
Near-term Plans
Before EOS is available, a number of remote sensing missions are
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expected to study ocean circulation and air-sea fluxes of energy and mo-
mentum. They include the precision altimetry mission, TOPEX/Poseidon;
the sea-surface temperature measurements, altimetry, and a surface wind
measuring scatterometer on the European Space Agency's ERS-1; the
NASA scatterometer on the Japanese ADEOS; and an altimeter to be
flown by the U.S. Navy on a Special Purpose Inexpensive Satellite (SPIN-
SAT). These are to be complemented by ongoing operational measurements
of sea surface temperature and humidity from the NOAA and Defense Me-
teorological Satellite Program (DMSP) programs. The various missions are
intended to provide data for existing and planned field programs such as
the World Ocean Circulation Experiment.
EOS Plans
The primary EOS measurements are intended to provide a variety of
data on ocean currents, surface winds, ocean and atmospheric tempera-
tures, and near-surface humidity for air-sea flux studies. They include sea-
surface temperature from the Moderate Imaging Spectrometer in its nadir
mode, and from the High Resolution Microwave Spectrometer Sounder.
Both the classical fan-beam (STIKSCAT) and advanced dual pencil-beam
(SCANSCAT) scatterometer designs are being considered for EOS. Surface
topography would be measured from an altimeter. Air temperature and
humidity near the sea surface would be measured with the Atmospheric
Infrared Sounder and the Advanced Microwave Sounding Unit.
3. How will changes in climate affect temperature, precipitation,
and sod mozsmre patterns, and the general distribution of water and
ice on the land surface?
Near-term Plans
Specific missions proposed in this general area are the joint U.S./
Japanese Topical Rainfall Measuring Mission (TRMM) and a planned
French mission, Bilan Energetique de 1a Systeme Tropical (BEST). Each
mission proposes to carry a major radar sensor for measuring rainfall
directly, and together they would form the space-based portion of the
Global Energy and Water Cycle Experiment, which is scheduled to begin in
the mid-1990s. Of the two satellite projects, TRMM is more fully developed
in its technical planning.
EOS Plans
The primary EOS measurements in this area are for temperature and
water vapor sounding from AIRS and AMSU. Precipitation, sea ice, and
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Spectrometer Sounder (HIMSS). Glacier profiles would be measured by
the Geosciences Laser Ranging System (GERS). Water vapor fluxes would
be monitored by the scatterometer and HIMSS over the oceans. Over
land, tropospheric winds, aerosols, and cirrus clouds would be monitored by
the Laser Atmospheric Wind Sounder (LAWS). Vegetation characteristics
would be measured by the Moderate Resolution Imaging Spectrometer
(MODIS), the High Resolution Imaging Spectrometer (HIRIS), and the
Intermediate Thermal Infrared Radiometer (ITIR).
Recent aircraft nights demonstrate that soil moisture can be mea-
sured from space with a Synthetic Aperture Radar (SAR). Monitoring soil
moisture is important for study of the hydrologic budget, but is not in-
cluded in current EOS plans because of budget considerations. Although
soil moisture can- and should be measured on the ground, only satellite
measurements can provide global coverage continuously. The LAWS in-
strument will also require extensive development of technology to achieve
the highest level of proposed precision.
Engineering considerations presented by NASA suggest that the SAR
instrument contemplated for EOS would not be compatible with a multi-
instrumented satellite. Therefore, the potential contributions of a free-
flying SAR mission should be carefully considered in the context of global
change research.
4. How can the reliability of global- and regional-scale climate
predictions be improved?
The EOS and other space-based observing missions are expected to
make major contributions toward answering this question in a number
of ways. First, improved understanding of processes obtained from the
respective missions would be incorporated into better process descriptions
in models. Second, data from the missions-either archived directly or
assimilated into the data streams of current global weather prediction
systems- would provide climate data sets invaluable for validating models
to be used for projecting climate change. Third, many of the boundary
conditions for models used for climate projections must be derived and
improved from satellite observations. Finally, predictions for the satellite
data can provide initial conditions needed for the shorter seasonal to
interannual time scales.
Biogeochemical Dynamics
1. What is the relative importance of the oceans and terrestrial
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biosphere as sinks for fossil fuel carbon disciple, and how do they
change with time?
Near-term Plans
Monitoring the distribution of oceanic chlorophyll and the properties
of terrestrial vegetation provides information on gas and nutrient exchange
between the atmosphere and ocean, freshwater and terrestrial biosphere,
and on oceanic and terrestrial carbon storage. The role of biological systems
in global change is one of the least understood. The precursor missions and
the EOS planning in this area are key parts of the global change research
program and should have high priority.
The international Joint Global Ocean Flux Study (JGOFS) has been
developed and has a field program now beginning. Currently, the Sea-
viewing Wide Field Sensor (SeaWiFs) ocean color mission is planned to
support JGOFS. Flight of the Shuttle Imaging Radar (SIR-C) is important
for studies of land vegetation, and will be complemented by field studies
of the World Climate Research Program (e.g., the International Satellite
Land Surface Climatology Program and the Global Energy and Water Cycle
Experiment) and the International Geosphere-Biosphere Program (e.g., the
Joint Global Ocean Flux Study).
EOS Plans
The Moderate Resolution Imaging Spectrometer (MODIS) in both its
nadir-viewing (MODIS-N) and side or tilt-viewing (MODIS-T) implemen-
tations is the essential next step for measuring ocean and land chlorophyll
concentration. The high spectral resolution of the MODIS is intended to
provide measurements not possible before. The MODIS, the high,spectral
resolution HIRIS, the Intermediate Thermal Infrared Radiometer (ITIR),
and the Multi-Angle Imaging Spectro-Radiometer (MISR) are expected
to collect land vegetation measurements. Biogenic gas emissions could be
measured by the Tropospheric Emission Spectrometer (TES), and vegeta-
tion structure could be monitored with the NASA SAR.
Findings
Current plans omit important space-based measurements that would be
valuable for understanding the relative importance of ocean and terrestrial
ecosystems as sinks for carbon dioxide. First, in the near term, the JGOFS
program would benefit from the flight of the next generation of ocean
color instrument, the proposed SeaWiFS. Second, the SAR has potentially
important roles to play in making measurements of biological processes on
land.
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2. What are the major sources responsible for the current increases
in atmospheric nitrous oxide and methane?
3. What are the implications for stratospheric ozone global) and
in polar regions increased concentrations of chlorine and bromine?
Near-term Plans
In the near term, the Upper Atmosphere Research Satellite (WARS)
and the continuing in situ Global Tropospheric Experiment (GTE) with its
Pacific Exploratory Mission in 1991 and an Atlantic program in 1992-will
address these two questions in the interval before the first EOS satellite is
launched.
EOS Plans
For these studies, it is important to monitor solar radiation to the
earth. It is proposed that solar output be monitored by the Solar Stellar
Irradiance Comparison Expenment (SOLSTICE) and the Active Cavity Ra-
diometer Irradiance Monitor (ACRIM). SOLSTICE should provide precise
daily measurements of the full disk solar ultraviolet irradiance; ACRIM is
designed to monitor the variability of total solar irradiance with state-of-
the-art accuracy and precision.
The Tropospheric Emission Spectrometer is proposed to measure tro-
pospheric trace gas species. This high-resolution infrared imaging spec-
trometer would generate three-dimensional profiles on a global scale of
virtually all infrared-active species from the surface to the lower strato-
sphere. The Measurement of Pollution in the Troposphere (MOPING)
and lloposphenc Radiometer for Atmospheric ChemistIy and Environ-
mental Research (TRACER) instruments are intended to monitor carbon
monoxide in the troposphere.
The High-Resolution Dynamics Limb Sounder (HIRDLS) is expected
to observe the global distribution of temperature and concentrations of
ozone, water vapor, methane, various oxides of nitrogen, CFCs, and
aerosols in the upper troposphere, stratosphere, and mesosphere.
The Spectroscopy of the Atmosphere Using Far Infrared Emission
(SAFIRE) instrument is inended to provide simultaneous measurements of
HO, NO=, ClO=, and Brow species. The Microwave Limb Sounder (MLS),
an enhanced version of an instrument on WARS, would provide vertical
profiles of all molecules and radicals believed to be important in the ozone
destruction circle in the stratosphere and mesosphere. The Stratospheric
Wind Infrared Limb Sounder (SWIRLS) is expected to provide direct
measurements of stratospheric winds by measurements of Doppler shift.
This would allow correlation of atmospheric dynamics and chemistry in the
stratosphere. Together with the Stratospheric Aerosol and Gas Experiment
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(SAGE III) instrument, a full set of data should be provided to help answer
questions about these phenomena.
Ecological Systems and Dynamics
1. What ecological systems are most sensitive to global change, and
how can natural change in ecological systems be distinguished from
change caused by other factors?
2. What are the likely rates of change in ecological systems because
of global change, and will natural and managed systems be able to
adapt?
~,
3. How do ecological systems themselves contribute to processes of
global change?
Near-term Plans
The satellite data required to address the above questions comes
in the near term from research and operational missions. The ongoing
NOAAlAVHRR, Landsat, and SPOT programs provide detailed informa-
tion on ecological systems primarily on land. Data from these programs
can be used to monitor changes in land use patterns and the areal extent of
vegetation representative of ecosystem types. As described earlier, current
proposals include the flight of an ocean color instrument.
EOS Plans
The EOS contribution to these research objectives should be made
by the same instruments that are intended to contribute to research on
biogeochemical dynamics: MODIS-N and -T. HIRIS, MISR, and ITIR.
The SAR instrument, which could make additional contributions in this
area, is not included in current plans for EOS. The EOS instruments would
provide data similar to those of the NOAAlAVHRR, Landsat, and SPOT
programs but with higher spectral resolution and accuracy for studying
ecological processes in detail.
Earth System History
1. What are the natural ranges and rates of change in the climate
and environmental systems?
2. How rapidAy have ecosystems adapted to past abrupt transitions
in climate?
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3. Do past warm intervals in Earth history provide appropriate
scenarios to test model predictions of future global warming?
The answers to these questions are expected to come primarily from in
situ studies of cores from continental, ice, and ocean drilling. Current space-
based observations cannot directly reveal global changes in the Earth's
history, but they can provide data useful for improving understanding of
solid Earth processes, which would help to illuminate that history. (See the
section on Solid Earth Processes below.)
lIuman Interactions
1. What kinds of empirical data are needed to measure and under-
stand human interactions in global change?
The EOS program should provide data that will be potentially useful
for the human interactions aspect of the USGCRP. For example, the very
high resolution instruments such as HIRIS could provide information on
direct human interactions with the environment (e.g., deforestation, coastal
and estuarine pollution, agricultural practices). EOSDIS is expected to be
an important source of such data for the study of the effects of human
activities on the environment. In order that the use of these data be
effective, there will be a need for close interaction between researchers
who will use these data for this purpose and the EOSDIS designers to
ensure that the system provides the required information.
2e How and why do human beings and human systems influence
physical and biological systems?
The answer to this question drill depend partly on the use of satellite
data, which can provide an important means of studying and monitoring
the effects of some human activities on the environment.
Solid Earth Processes
1. How do different coastal regions respond geologically and ecolog-
ica11y to higher sea level, and how can the contributions from changes
in climate (e g., glacier melting and ocean warming be differentiated
from those due to tectonic processes?
2. What are the magnitude, geographic location, and frequency of
volcanic eruptions and their effect on climate?
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3. How do permapost regions of the Northern Hemisphere respond
to climate warming?
Near-term Plans
The near-term activities in this area include the precise positioning
provided by the Global Positioning System, the Very Long Baseline Inter-
ferometry, and Laser [lacking of the LAGEOS I and II satellites. These
missions support the use of global tide gages and satellite altimeter mea-
surements of sea level change, as well as altimeter measurements of changes
in global ice mass. Imaging of volcanoes and other regions will be pro-
vided by various operational satellites (AVHRR on the NOAA satellites
and imagers on Landsat and SPOT). Emissions from volcanic eruptions will
be monitored by the operational meteorological satellites and the SAGE
instruments. Beginning in 1991, UARS will provide useful data on the
stratosphere.
EOS Plans
Crustal movement and tectonic plate deformation are proposed to be
monitored by the Geoscience Laser Ranging System (GLRS), which will
early a laser system, an optical tracking system, and a precise navigation
system for use with arrays of reflectors on the ground. The Altimeter
and Global Positioning System Geoscience Instrument (GGI) should be a
source of accurate ice and ocean topography. The SAR, which is currently
not budgeted, could provide all-weather studies of surface processes.
Surface mineral identification, soil characteristics, and geothermal
monitoring would be carried out with the ITIR and HIRIS. Monitoring
of trace gases and aerosols is intended to be done with SAGE, TES, and
HIRIS.
EOS data should be useful in characterizing the nature of volcanic
emissions, for monitoring the mechanisms of plate motion over long periods,
and for understanding regional uplift, subsidence, and associated coastal
processes. Changes in the Earth's rotation and length-of~ay could be
monitored by EOS with high resolution geodetic techniques, while the deep-
seated processes in the Earth that cause these changes may be inferred from
studies of the Earth's magnetic field. EOS sensors are expected to monitor
surface processes and detect areas of current or potential desertification
and erosion.
Solar Influences
1. What aspects of solar variability are influencing the stratospheric
ozone layer?
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49
2. What impact do other inputs, fig, panicles, have on the upper
atmosphere and how are they coupled to other a~nosphenc regions?
3. How does the sun's output vary and what is its impact on
terrestrial climate?
Near-term Plans
Providing answers to these questions will require accurate measure-
ments of solar variability at all wavelengths and continuing monitoring of
appropriate chemical species in the upper atmosphere. These measure-
ments are being made by NOAA operational satellites. Near-term plans
include instruments on WARS, as described earlier in connection with the
discussion of biochemical dynamics. The data are needed for further de-
velopment of theoretical models of solar-terrestrial interactions that affect
global change.
EOS Plans
Of particular importance here is ultraviolet radiation from the sun.
The EOS Solar Stellar Irradiance Comparison Experiment (SOLSTICE) is
intended to monitor the full disk solar ultraviolet irradiance as a follow-on
to a similar instrument carried by WARS.
The EOS Stratosphere Aerosol and Gas Experiment III (SAGE III)
is proposed to measure profiles of aerosols, air density, and a number of
constituents. It is an extension of the successful SAGE experiments flown
earlier and planned for WARS. SAGE III is also planned for flight on the
Space Station to provide full coverage and back-up measurements.
EOS proposes to measure solar irradiance with a radiometer (the
Active Cavity Radiometer Irradiance Monitor) and with an ultraviolet
irradiance measurement. Each of these is a source of continuity with
UARS measurements.
Representative terms from entire chapter:
situ measurements
