SP-401 Skylab, Classroom in Space

[118] Part II - Student Experiments

 

Chapter 11: Observing Earth from Space.

picture of two astronauts aboard Skylab

 

[119] Observations of certain physical characteristics of Earth and its atmosphere were the objectives of two of the Skylab student investigators. One devised a method of predicting volcanic activity from space, while the other developed a technique for measuring air pollution and its effects.

Remote sensing of Earth's characteristics, whether by electronic scanners or photography, is based on the energy radiated and reflected by it. Every object radiates and absorbs a characteristic spectrum of energy typical of the object's composition and temperature. During daylight hours, the solar energy absorbed and reradiated from the surface masks the thermal energy generated by and emitted from Earth itself.

Skylab was equipped with sensors capable of measuring the energy, both emitted and reflected, from a relatively small area of Earth's surface. The spectral bands for which these sensors could detect this energy lay in the radar, infrared, visible, and ultraviolet regions.

Infrared energy (the region of primary interest) is electromagnetic radiation of wavelengths longer than visible light, but shorter than radar wavelengths. The measurement of infrared energy radiated and reflected from crop lands, forests, and oceans is very useful in assessing the condition of vegetation, ocean temperatures, and other characteristics of Earth. It is possible to determine the temperature of a body from an analysis of the thermal infrared energy that it radiates in the band of wavelengths from 10.2 to 12.5 micrometers.

 

Volcanic Study

Since the 16th century, volcanic eruptions have caused over 200 000 known deaths and destroyed much valuable vegetation. One reason for this catastrophic loss of life is that volcanic activity is not predictable. As a possible method of predicting when volcanic eruptions might occur, Troy A. Crites of Kent Junior High School, Kent, Wash.,....

 


Mount Rainier, in Washington, is a dormant volcano that helped spark the interest of Troy Crites in studying such geographical features of Earth from Skylab. (Courtesy Dr. C. H. Murrish).

Mount Rainier, in Washington, is a dormant volcano that helped spark the interest of Troy Crites in studying such geographical features of Earth from Skylab. (Courtesy Dr. C. H. Murrish).



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pictures of Troy Crites

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Troy Crites proposed monitoring volcanoes by measuring their infrared energy as Skylab orbited over them. He is shown, above, at the Marshall Space Flight Center greeting Astronauts Russell Schweickart and Owen Garriott; Leland Belew, Manager of Marshall Space Flight Center's Skylab Program; and David Newby, Director of Administration and Technical Services.

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Troy Crites proposed monitoring volcanoes by measuring their infrared energy as Skylab orbited over them. He is shown, above, at the Marshall Space Flight Center greeting Astronauts Russell Schweickart and Owen Garriott; Leland Belew, Manager of Marshall Space Flight Center's Skylab Program; and David Newby, Director of Administration and Technical Services.

 

[121] ....proposed the use of infrared sensors on Skylab to detect changes in the heat emitted from known volcanoes.

Some progress has been made in predicting impending volcanic activity. Warnings are sometimes provided by the melting of ice caps, the disappearance of crater lakes, the drying up of springs and wells, the death of surrounding vegetation, or an unexplained evacuation of wildlife. Other attempts to predict volcanic eruptions have generally relied upon direct measurements. Temperatures have been measured at or near the surface of volcanic mountains, and the shape of volcano slopes has been measured in the hope that detection of an increase in temperature or an actual swelling of the mountain caused by an upward movement of lava would indicate an impending eruption. An increase in frequency and strength of Earth tremors detected by seismographs can also indicate that the lava under volcanoes is welling up and that an eruption may occur. Recently, data from tiltmeters, seismographs, and other instruments have been collected by satellites from sensors located on remote volcanoes and transmitted to laboratories where scientists can study them.

Crites' experiment was intended to determine whether or not infrared sensors in a satellite would be able to detect the heat flow from individual volcanoes. If so, heat radiating from active volcanoes could be periodically measured by the orbiting sensors and their normal heat-emission rate established. An observed increase in the rate might then be used to predict an eruption. He proposed to use data from Skylab instruments that recorded thermal radiation in the infrared region. These instruments and cameras were part of Skylab's Earth observation experiments. Data were obtained from Mount Etna and a volcanic region in Nicaragua during the mission. Information in the form of computer printouts was obtained at 6.2, 10.2, 12.5, and 15.5-micrometer wavelengths.

 


Volcanoes active, dormant, and extinct are scattered throughout the world, and the Pacific Ocean is sometimes said to have a << rim of fire. >> (introduction to geophysics , by b.f. howell. used by permission mcgraw-hill book co. ) [Link to a larger picture]

Volcanoes active, dormant, and extinct are scattered throughout the world, and the Pacific Ocean is sometimes said to have a "rim of fire." (Introduction to Geophysics, by B.F. Howell. Used by permission of McGraw-Hill Book Co.)


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Crites proposed measuring the heat energy radiated from Telica and Cerro Negro, two volcanoes in Nicaragua.

Volcanoes Telica and Cerro Negro were photographed in true color from Skylab.

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Volcanoes Telica and Cerro Negro were photographed in true color from Skylab.

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The same two volcanoes were photographed in color infrared from the space station.

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Crites proposed measuring the heat energy radiated from Telica and Cerro Negro, two volcanoes in Nicaragua.

The same two volcanoes were photographed in color infrared from the space station.


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[Top] Mount Etna, on the island of Sicily, was photographed in true color from Skylab just 3 months before an eruption. It is in the lower right corner of the picture.
[Bottom] A fuming Mount Etna was also photographed by the crew of the second Skylab mission in color infrared.

[Top] Mount Etna, on the island of Sicily, was photographed in true color from Skylab just 3 months before an eruption. It is in the lower right corner of the picture.

[Bottom] A fuming Mount Etna was also photographed by the crew of the second Skylab mission in color infrared.



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picture of Joe Zmolek

Joe Zmolek is greeted by Astronauts Russell Schweickart and Owen Garriott, Leland Belew, and David Newby at the Marshall Space Flight Center.

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Joe B. Zmolek, who proposed a Skylab experiment for measuring pollution in the atmosphere, went to Notre Dame University, where he majored in premedicine. Above right, he is greeted by Astronauts Russell Schweickart and Owen Garriott, Leland Belew, and David Newby at the Marshall Space Flight Center.

 

Atmospheric Attenuation of Energy

Atmospheric pollution has become one of the major problems for people in industrialized countries. Little fundamental information is available from which to judge the long-range effects of such pollution. Joe B. Zmolek of Lourdes High School, Oshkosh, Wis., proposed investigating the feasibility of measuring the amount of energy absorbed and dispersed by the atmosphere. Such measurements would establish a data base to support future investigations of atmospheric changes, particularly those brought about by man's pollution.

Several of Skylab's Earth observation instruments were used in conjunction with ground-based instruments to measure the attenuation, or reduction, of solar-energy radiation in the visible and near-infrared regions of the spectrum as the energy passed through the atmosphere. The degree of attenuation was to be determined by comparing the energy received at Earth's surface with the energy entering Earth's atmosphere. Attenuation of energy reflected through the atmosphere from Earth was to be determined by comparing energy measurements made just above its surface with simultaneous measurements made from Skylab.

[125] Data were to be collected over sparsely and densely populated regions to permit evaluation of both natural and man-induced atmospheric conditions.

Ground data were obtained by NASA personnel at selected sites in the United States, using a spectral pyranometer. This is an instrument that measures radiant energy at selected wavelengths. The pyranometer was first pointed upward to measure the energy coming from the Sun to provide a comparison with previously recorded data. It was then inverted to measure the radiation reflected from Earth at the same time that Skylab was passing overhead and also measuring radiation from the site.

Skylab data were obtained by six cameras using visible light and infrared film and filter combinations and by electronic instruments that measured energy levels in spectral bands from 0.4 to 2.4 micrometers. The cameras took pictures simultaneously, each covering a different portion of the visible and infrared spectra.

On June 5, 1973 (during the first manned period), Zmolek was in Texas at the Houston Area Test Site, one of the ground sites assigned for his experiment. He acquired the necessary ground data but, unfortunately, the clouds over the site prevented Skylab from collecting data at the same time. However, the space station made a marginal data pass over the White Sands, N. Mex., site on June 14.

During the second manned mission, an experiment was conducted over Phoenix, Ariz., on September 6. On that occasion, data were gathered not only by Skylab instruments but also by six similarly instrumented aircraft over the site. Data were acquired at test sites upwind and downwind of Phoenix, providing, in effect, information from a relatively pollution-free atmosphere as well as from a polluted atmosphere.

During the third mission, data were gathered once at Houston and twice at White Sands. However, neither ground nor aircraft data were obtained.

Zmolek's experiment produced a large volume of data that has not yet been completely analyzed. Since the study of atmospheric conditions has been a subject of intensified interest to scientists and engineers for at least the past 50 years, the experiment may give added impetus to this area of investigation. The continual measurement from a satellite of the attenuation of solar energy could....

 


Using a pyranometer, Joe Zmolek measured the energy received from the Sun as well as that reflected by the Earth. [Link to a larger picture]

Using a pyranometer, Joe Zmolek measured the energy received from the Sun as well as that reflected by the Earth. Simultaneous measurements were made from Skylab and aircraft. Such studies could help determine the effects of atmopsheric pollution on Earth's heat-energy balance.


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Data from Zmolek's experiment were to have been gathered from areas near Houston, Phoenix, and White Sands, N. Mex.

Data from Zmolek's experiment were to have been gathered from areas near Houston, Phoenix, and White Sands, N. Mex. However, clouds often obscured the view. The second crew of Skylab managed to take this picture of Phoenix on an exceptionally clear day.

 

....assist in the prediction of weather conditions and aid in determination of the overall effect of pollutants in the air.

Thus, the combination of instruments aboard Skylab and the scientific curiosity and imagination of two high school students produced information about one of the most awesome and potentially destructive geological features of Earth and helped open the way to measuring on a large scale the pollution of its atmosphere.

 


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The same view of Phoenix was also made in color infrared, showing such natural features as Salt River joining Gila River just downstream from the confluence of the Gila and the Agua Fria Rivers.

The same view of Phoenix was also made in color infrared, showing such natural features as Salt River joining Gila River just downstream from the confluence of the Gila and the Agua Fria Rivers.


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