Assessment of Satellite Earth Observation Programs--1991 (1991) / Chapter Skim
Currently Skimming:
2 Earth Science From Space
2 Earth Science From Space
Pages 3-35
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 3... ...
It is important to emphasize at the outset, however, that although these reports have assisted NASA in developing its Earth observation flight programs and related research plans, the agency also receives advice in this area from other groups. Numerous other advisory reports-by several other NRC committees and internal NASA REPORT MENU advisory bodies-have collectively produced an interrelated advisory framework NOTICE covering all aspects of civil Earth observation programs and policies.
|
From page 4... ...
global biology, ecology, and biogeochemical cycles. The major scientific objectives for space-based observations, as outlined in the previous SSB reports (1982a, 1985, 1986)
|
From page 5... ...
surface wind, atmospheric temperature and humidity, and stress over the oceans, and land and sea surface temperature; (ii) precipitation and closely related surface characteristics including soil moisture, snow and ice cover, and vegetative biomass; (iii)
|
From page 6... ...
The usefulness of satellite instruments such as AVHRR for assessing snow and ice cover and relative changes in biomass has been demonstrated, but much remains to be done to advance the capability for assessing these surface properties, as well as soil moisture, from space. Significant progress also has been made in the use of space observations to determine the properties of clouds from space.
|
From page 7... ...
. These instruments will provide substantial improvements in the measurement of surface stress over the sea, of land and sea surface temperature, of cloud properties, and of vertical profiles of temperature and water vapor.
|
From page 8... ...
The proposed EOS SAR, which would fly as a separate mission, could make important contributions to the determination of the properties of sea ice and snow, soil moisture and surface water distribution on land, and vegetative structure, all of which interact in significant ways with the troposphere. Additional Needs The AVHRR instrument on the NOAA polar orbiters, and the VAS and VISSR instruments on the NOAA GOES are providing important historical data sets for future climate change studies, in particular, for the early versions of the EOSDIS.
|
From page 9... ...
Finally, it is important for NASA to continue the development of an instrument that could obtain the important global wind field measurements. The Stratosphere and Mesosphere Science Objectives According to the 1985 SSB/CES report, the highest-priority objectives for the study of the stratosphere and mesosphere from space are as follows: 1.
|
From page 10... ...
These measurements should go far toward meeting the scientific objectives for the stratosphere and mesosphere, which are aimed largely at understanding the natural and anthropogenic mechanisms for seasonal and interannual variability and long-term trends in ozone, associated trace gases, and large-scale circulation. Beginning with the launch of EOS-A, the High-Resolution Infrared Dynamical Limb Sounder (HIRDLS)
|
From page 11... ...
CLIMATE STUDIES Science Objectives The highest-priority objectives established by the 1985 SSB/CES report for the study of long-term climatic changes from space are the following: 1. To measure the long-term global and regional trends in external and internal climate forcings: the variables that must be measured are the solar flux, the radiative fluxes at the top of the atmosphere, radiatively important trace gases and aerosols, and certain land-surface properties (vegetative cover, soil moisture, albedo, and emissivity)
|
From page 12... ...
Anticipated Improvements Precise monitoring of the solar input radiation will be extended by UARS. The CERES instrument on UARS will help to extend the observational record of the top-of-the-atmosphere radiation budget, and continued processing of historical data sets on cloud properties under the ISCCP will add to our ability to monitor the radiation budget and cloud interactions.
|
From page 13... ...
To measure sea-surface temperatures. The science objectives for biological oceanography are discussed later in this chapter.
|
From page 14... ...
It is important to recognize that it is the surface skin temperature, measured by the infrared satellite instruments, that is the correct SST estimate for the computation of air sea heat flux. Environmental satellite sensors are constrained to directly measuring only properties at or very near the sea surface and thus are incapable of directly observing any subsurface properties.
|
From page 15... ...
This technique is similar to the computation of winds by tracking clouds in sequential satellite images, and has been applied successfully to tracing sea ice in visible and infrared images, and SST patterns in infrared images. Preliminary approaches to this problem have been based on the use of AVHRR data.
|
From page 16... ...
Also, the continuation of the high-precision altimeter measurements initiated by the TOPEX/Poseidon mission is required to monitor the ocean circulation and its variability. CRYOSPHERIC RESEARCH Science Objectives The objectives for cryospheric research have been articulated in several documents produced by the NRC.
|
From page 17... ...
To measure the horizontal extent, velocity, surface temperature, albedo, and topography of the world's sea and lake ice cover and to distinguish between different ice types. To measure the topography of the upper and lower surfaces, thicknesses, surface areas, surface temperatures, albedo, and internal structure of the world's major glacial ice sheets and shelves.
|
From page 18... ...
Anticipated Improvements The primary scientific objectives for snow and ice studies that can be addressed with EOS data later in this decade are as follows: To improve understanding of the influence of snow and ice on the global radiation balance, including an assessment of the importance of ice-albedo feedback as a mechanism for climate change. To improve our understanding of the role of snow and ice in the hydrological cycle, including fresh water supply, and in sea level change.
|
From page 19... ...
The potential contributions of the free-flying, multifrequency EOS SAR for earth studies are numerous. In the context of cryospheric research, the EOS SAR would be the best way to routinely monitor the details of sea ice cover, concentration, type, and movement, and of ice sheet dynamics.
|
From page 20... ...
The measurement of components of the water balance, such as fresh water runoff, soil moisture, precipitation, and evapotranspiration, presents one of the most difficult challenges to satellite remote sensing. With the exception of passive microwave sensors, such as the Nimbus-7 SMMR and the DMSP SSM/I, there has been relatively little progress in defining and implementing satellite methods for the observation of these parameters.
|
From page 21... ...
The development of two of the most useful instruments for hydrologic research, the HIRIS and EOS SAR, has unfortunately been delayed, and neither is likely to fly until after the turn of the century. The multi-frequency, multi polarization, multi-look-angle EOS SAR in particular has the potential to provide the best assessments of biomass and soil moisture on a global basis.
|
From page 22... ...
The development of instruments with an enhanced thermal infrared sensing capability would improve the mapping of rock units in the continents. The lower-resolution NOAA AVHRR and Landsat Multispectral Scanner (MSS)
|
From page 23... ...
Until recently, the Soviets had the only operational radar imaging capability, but as noted above, ESA is planning to launch its own radar on the ERS-1 mission in 1991, which will be followed by Japanese and Canadian missions in 1992 and 1994, respectively. During the EOS time frame, the high spatial resolution coupled with the very large number of spectral bands of the planned HIRIS instrument would represent the next major step, as a follow-on to the Landsat and SPOT instruments, in monitoring the land surface from space.
|
From page 24... ...
The committee endorses NASA's preliminary plan to fly a topographic mission in the late 1990s and considers such a mission to be important for both geologic and hydrologic studies. GEODYNAMICS Science Objectives The primary science objectives identified in the 1982 SSB/CES report for the study of solid-earth dynamics from space, in order of priority, are as follows: 1.
|
From page 25... ...
The development and demonstration of the SLR and VLBI techniques for measuring plate motion and for measuring variations in the Earth's rotation rate have been major accomplishments by NASA during the 1980s. The SLR and VLBI techniques provide the capability for defining and maintaining an accurate terrestrial reference frame, which is necessary for monitoring long-term changes in global plate motions and for monitoring secular trends in ice sheet topography and mean ocean surface.
|
From page 26... ...
Flying the ALT in a polar orbit as currently planned, however, would not be optimal for this measurement. Although the EOS-B ALT will be a TOPEX/Poseidon-class nadir-pointing instrument, its flight in a polar orbit would not provide either a more accurate oceanic geoid or more precise measurements of ocean circulation than earlier altimeters; however, it would provide estimates along a different ground track.
|
From page 27... ...
GLOBAL BIOLOGY, ECOLOGY, AND BIOGEOCHEMICAL CYCLES Land-Surface Vegetation Science Objectives The scientific objectives identified in the 1986 SSB/CPB report for studying land-surface vegetation on a global basis are as follows: Measure total area covered and geographic distribution of major biomes. Measure the rate of change of distribution of major biomes.
|
From page 28... ...
Anticipated Improvements During the EOS time frame, the MODIS will provide greatly improved spectral resolution of the land surface. Studies have been and are being conducted to develop sampling strategies on selected biomes.
|
From page 29... ...
The EOS SAR has the potential to measure global biomass and to assess surface soil moisture, but not the soil water content throughout the root zone of most plants. Surface soil moisture is useful in assessing runoff and, therefore, important in constructing the water balance.
|
From page 30... ...
Fresh Water, Wetlands, and Estuaries Science Objectives The 1986 SSB/CPB report established the following scientific objectives for the study of fresh water, wetlands, and estuaries from space: For the 20 largest rivers, determine annual rate of transport of carbon, nitrogen, sulfur, and phosphorus from land to oceans. Determine area covered and geographic distribution of coastal wetlands.
|
From page 31... ...
Similarly, NOAA's sponsorship through the Small Business Innovation Research program for small companies to develop a remote sensing instrument package for estuarine observations from small, single-engine aircraft is providing researchers with an inexpensive option for wetland and estuarine studies. Anticipated Improvements The committee expects that the spectral resolution of the future HIRIS instrument on EOS will enable researchers to further improve biomass and stress measurements in temperate wetlands, and to extend them to freshwater and tropical wetlands.
|
From page 32... ...
A thermal infrared radiometer will be used to measure surface temperature, and a microwave radiometer, which is at present being reduced in size, will be used to measure water salinity. Deployed in conjunction with high resolution satellite sensors such as HIRIS, these airborne sensors should be able to observe tidal, seasonal, and annual variations and spatial distributions of phytoplankton blooms, sediment plumes, estuarine fronts, circulation patterns, and other estuarine phenomena.
|
From page 33... ...
These newly formed branches are focused on the following: Cycling of carbon and key nutrients within ecosystems, and between ecosystems and their abiotic environment; Identification of sources of radiatively and chemically active trace gases; and Quantification of major exchanges of these gases between the Earth's biosphere and its atmosphere. Progress over the previous five, years toward understanding the role of the ocean biota in global biogeochemical cycles of carbon, nitrogen, sulfur, and phosphorus has focused on efforts to quantify the effects of phytoplankton.
|
From page 34... ...
The HIRIS instrument, expected to eventually fly in the EOS program, would enable critical regional process studies. As discussed above, efforts are under way to build the SeaWIFS, which will have eight spectral bands ranging from about 400 nm to 890 nm.
|
From page 35... ...
Although the Thermal Infrared Multispectral Scanner (TIMS) acquires data in six channels between 8 µm and 12 µm, and ASTER will acquire data in several channels in this region, there is significant interest in higher spectral resolution measurements from both airborne and spaceborne platforms, and at the present time these are not planned.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.