Mission to Planet Earth Space Science in the Twenty-First Century -- Imperatives for the Decades 1995 to 2015 (1988) / Chapter Skim
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3. The Earth as a System--A Global Perspective for Future Planning
3. The Earth as a System--A Global Perspective for Future Planning
Pages 52-72
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From page 52... ...
The task group draws upon these statements of progress and problems to attempt a synthesis through the identification of grand themes 52
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From page 53... ...
The necessity for extrapolation has widely differing time scales and reliabilities for different parts of Earth. The evolution of the Earth can also be viewed as a comprehensive process, starting from its formation out of the solar nebula and leading eventually to a state of stable stratification as internal energy sources run down (as they have on the Moon)
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From page 54... ...
Because satellites in orbit are external to the Earth, the answers they give are incomplete and must be supplemented by measurements at closer range or in situ, by laboratory experiments, and by theoretical modeling. Our discussion below identifies the global issues for each grand theme, and then specifies the measurements required.
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From page 55... ...
The geophysical and geochem~cal data must constrain the style of mantle convection and contribute to the understanding of earth evolution and the nature of the energy sources. The lithospheric plates are the cold, surface boundary layers of mantle convection cells, but several aspects of mantle convection are poorly understood.
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From page 56... ...
The Measurements Required Structure and Chemistry A number of specific measurements are required to describe, in three dimensions, the variation of physical parameters and chemical/m~neralogical composition at all depths within the Earth's interior. These include global seisrn~c wave propagation studies to describe lateral heterogeneities up to at least spherical harmonic degree and order 20.
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From page 57... ...
A global array of digital seismometers and geodetic devices telemetering via satellites to central ~observatoriesn is the solid Earth equivalent of a versatile, multispectral telescope or a largeaperture radio telescope. The inside of the Earth is now a candidate for imaging just as are other objects in the universe.
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From page 58... ...
These include: electromagnetic measurements (satellite studies of the time variability of the electromagnetic field can be used to obtain the distribution of electrical conductivity within the Earth's mantle, electrical conductivity being a sensitive measure of the tempera ture within the mantle) ; ground deformation measurements (GPS, corner reflectors, readily deployable strainmeters)
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From page 59... ...
Geological maps are also critical in that they supply constraints to models. For example, it is important to develop modem that relate strain buildup, fault slip, and earthquake occurrence to rheological properties of the crust and lithosphere.
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From page 60... ...
More generally, analysis of coupled topography and gravity data allows the determination of subcrustal structure, gravity compensation models, and crustal theological properties. Clearly, adequate topography data must be an integral part of any gravity mapping mission.
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From page 61... ...
for the required spatial resolution. Electronic beam steering of the phased array would allow the appropriate swath width for complete global coverage.
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From page 62... ...
A variety of unaging and sounding instruments on geosynchronous and polar platforms wait be needled to obtain uniform global coverage. GRAND THEM1: 2: ATMOSPHERE, OCEANS, CRYOSPHERE, AND HYDROLOGIC CYCLE Global Awes The central theme 2~!
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From page 63... ...
precise measurements of geophysical parameters such as the solar constant, stratospheric ozone, stratospheric temperature and aerosol, atmospheric trace compounds, surface albedo, land biomass, sea surface temperatures and topography, concentration of chlorophyll in the oceans, global cloudiness, and rainfall patterns and soil moisture. Because the coverage has to be global and repetitive space satel, , lites are, in principle, ideally suited to provide these data consistently over time.
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From page 64... ...
predictions on a global scale. In order to achieve this, an observing program can be visualized that: ~ Provides long-term and consistent data on some of the key parameters such as sea surface temperature-, ice cover, albedo, stratospheric ozone, and solar constant, so that we can begin to test the modem at least on a decadal time scale.
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From page 65... ...
To do this we will need a global satellite network together with major in situ programs to measure: Ocean currents and mixing. This includes a network of polar-orbiting satellites to measure sea surface topography, building on the results from the Ocean Topography Experiment (TOPEX)
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From page 66... ...
The flux of latent heat in the form of water vapor from the surface to the atmosphere, and its subsequent release through the condensation/precipitation process, constitutes the largest single heat source for the atmosphere. Current rain gage networks on land are generally adequate to measure precipitation in heavily populated regions, but considerable standardization in worldwide observing and reporting practices is necessary.
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From page 67... ...
We emphasize again the role that ice-core and pelagic sediment studies can play in extending the record. GRAND TlIEME 3: LIVING ORGANISMS AND THEIR INTERACTION WITH THE ENVIRONMENT Global Issues The overall goal for the study of global biogeochemical cycles is to improve understanding of the geologic, atmospheric, oceanic, and biotic reservoirs and their interactions in order to mode!
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From page 68... ...
The Measurements Required The external information needed to model these processes includes the major biological sources and sinks of organic carbon and active nitrogen, and inputs of sulfur and other compounds from volcanic activity. Urban pollution is a topic all by itself, but Is a major regional source of tropospheric ozone, oxides of nitrogen, sulfur dioxide, and other ingredients of larger-scale problems like acid rain.
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From page 69... ...
GRAND THEME 4: INTERACTION OF HUMAN ACTIVITIES WITH THE NATURAL ENVIRONMENT Global Ares Human activities since the beginning of the industrial revolution have increased to such an extent that they must now be regarded as important factors in changing the environment. The effects are approaching a significant stage in altering the concentration of ozone and carbon dioxide in the atmosphere, in changing the surface properties by deforestation and erosion, and in other industrial and agricultural activities.
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From page 70... ...
Changes involving soil erosion, loss of soil organic matter, desertification, deforestation, overgrazing, diversion of freshwater resources, and increasing levels of air pollution and acid rain affect the physics, chemistry, and biology of the Earth. The Measurements Required Human hnpact Tropical deforestation has recently become a scientific issue of major concern, not only because it significantly decreases biological diversity, and leads to soil erosion and lo" of productivity, but aLso because it is quite possible that it modifies the regional cInnate in a substantial manner.
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From page 71... ...
Satellite observations integrated with observations on land and the oceans can provide basic data and can monitor soil erosion, desertification, fresh water depletion, variations in the concentration of carbon dioxide and ozone, and the occurrence of acid rain. Hazards The larger and larger conurbations that absorb much of the population increase enhance man's vulnerability to natural hazards, such as hurricanes and earthquakes, through dependence on longer and more complex systems of transportation and larger habitational structures.
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From page 72... ...
Eventually, this probably will be an important ingredient in any successful prediction program. The space-based geodetic observations must be integrated with a variety of surface observations, including seismic studies.
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