It was probably when Apollo astronauts, on the way to the Moon, first saw our home planet in its entirety from their unique vantage point in space that humans began to view Earth as a single entity, rather than a conglomeration of diverse political entities . To this day, astronauts on their first flights all note the absence of "painted" national boundaries, as they look down upon Earth from orbit. Instead, land, oceans, and clouds dominate the view.
As far back as the Apollo program, even before Landsat, scientists and others connected with the space program realized that earth-looking satellites, as their sensors improved, could provide a wealth of data and derived information about the Earth as a whole and about selected regions by operating in a coordinated way. Different spectral intervals, look angles, resolutions, etc. would provide complementary data sets useful in many applications. Thus, early on, the value of acquiring data from fleets of satellites was so compelling that planners began to devise programs that would supply such inputs. One variant would be to have different sensors on the same spacecraft. This next image was made as a composite using data supplied by land, meteorological, and oceanographic satellites that show clouds, land surfaces, and ocean water temperatures. It serves to introduce you to one of the main ideas in this Section: the Terra space platforms that bears five sensor systems which can gather data integrated spatially and in time which are invaluable in monitoring the Earth's natural systems and the impact of humans on such systems.
'Humans' is the keyword in the above paragraph. To the best of our knowledge, Earth is the only planet in the Solar System that supports life (although organic molecules may exist on one or more satellites of Jupiter and Saturn, and perhaps once on Mars [page 19-13]). Life, in all its myriad forms, virtually covers Earth. No matter where we look for it, we find it. Much of our planet's geophysical and biological phenomena take place in a relatively thin shell of fluid (the atmosphere and oceans) that is about as thin in proportion to the Earth as a sheet of paper wrapped around a basketball. Most other relevant life activities stay on the land surface,within an even thinner zone of the uppermost layers of soil and rock. And yet, the complex interactions between the biosphere and the geosphere all take place within that thin shell. Just about everything that concerns us as living beings depends upon the integrity of these shells of land, sea, and air.
The shells result from eons of dynamic processes that began as the Earth formed. These processes, taken together, constitute global change. Without global change, we humans and much of the rest of the biosphere would not exist, because global change generated an oxygen-containing atmosphere, our protective stratospheric ozone layer, and global temperatures that support life (due to the greenhouse effect) as we know it. Until the last few thousand years, global change has been dominantly a "natural" process.
Recent observations have led scientists to conclude that human activities contribute to global change, that our industrial and land-management practices increase the rate of change of several geophysical phenomena, and that some changes may be deleterious to the biosphere. Nations around the world have banded together in a wide range of scientific and policy-based activities to determine the nature of human contributions to global change and to determine the effect such changes can have on our lives. These are gathered under the umbrella known as the International Geosphere-Biosphere Program (IGBP), which is, in essence, a massive effort to understand and learn to manage the world's environments.
As one of several U.S. government agencies involved in the U.S. Global Change Research Program, NASA instituted the Mission to Planet Earth (MTPE) initiative which it later renamed Earth Science Enterprise (on the Net at ESE), based on the space-based constellation of satellites and sensors known as the Earth Observing System (EOS). This section deals with some of the observations obtained in recent years that have led to the formation of MTPE/EOS, why NASA established it, what NASA designed it to accomplish, how NASA approaches those goals, and what anyone can do with the data.† .† For some general information about this and related programs, click on NASA's Earth Observatory Home Page. Also, the EOS Program Office publishes a bi-monthly News booklet which can be accessed on the Internet at The Earth Observer or can be obtained through postal mail by emailing to the address found on that page.
We have already used the term "Earth System Science" and will fully explain its meaning on page 16-3. For now we will simply state that ESS is an amalgam of several major components, as depicted in this next diagram. These are well-established fields of study of the Earth. You may notice that 'System' is sometimes replaced by 'Systems'. The plural is favored by some practioners to connote the role of these components each as an interrelated system which act in consort as part of the overall System (this is similar to James Lovelock's idea of "Gaia"). Most use the singular which implies that the components are subsystems. In this sense, the Earth operates as a unified system in which various fields of scientific study concentrate on one of its different parts.