The SAGE III instrument was one of nine experiments on the Russian Meteor-3M spacecraft. It provides accurate, long-term measurements of ozone, aerosols, water vapor and other key parameters of Earth's atmosphere. These observations are crucial for providing a better understanding of how natural processes and human activities may influence our climate.
Since the 1950s, it has become increasingly clear that human activities are modifying the composition of the atmosphere on a global scale. As the result of industrialization, the concentration of carbon dioxide has increased by about 20% during this period. More recently, the stratospheric concentrations of chemically active gases containing chlorine, bromine, and fluorine have dramatically increased. These trends have created issues of global interest including global warming and declining levels of ozone (both globally and in the ozone "hole" in the Antarctic). It has become increasingly clear, however, that these processes do not occur independently of one another and can only be understood in the context of a global system. Accurate and precise measurements are needed to unravel complex and interactive relationships between chemical, radiative, and dynamical processes in the atmosphere, ocean, and on land. As a result, in 1991 NASA initiated a comprehensive program to understand the Earth's atmosphere, oceans, land, and cryosphere (ice and snow) as a single, complex, interactive system. NASA's Earth Observing System (EOS) consists of a series of spaceborne instruments to monitor crucial components of the Earth system, an advanced data handling system, and teams of scientists who will evaluate on-going climate change and predict future changes. Ultimately, EOS will produce scientifically sound recommendations for environmental policy to national and international bodies to mitigate or prepare for these changes.
SAGE III's role in the EOS program is to provide global, long-term measurements of key components of the Earth's atmosphere. The most important of these are the vertical distribution of aerosols and ozone from the upper troposphere through the stratosphere. In addition, SAGE III also provides unique measurements of temperature in the stratosphere and mesosphere and profiles of trace gases such as water vapor and nitrogen dioxide that play significant roles in atmospheric radiative and chemical processes.
SAGE III is a grating spectrometer that measures ultraviolet/visible energy. It relies upon the flight-proven designs used in the Stratospheric Aerosol Measurement (SAM I) and SAGE I and II instruments. The new SAGE III design incorporates Charge Coupled Device (CCD) array detectors and a 16 bit A/D converter. Combined, these devices allow for wavelength calibration, a self-consistent determination of the viewing geometry, lunar occultation measurements, and expanded wavelength coverage. SAGE III sensor assembly is illustrated below and consists of pointing and imaging subsystems and a UV/visible spectrometer. The pointing and imaging systems are employed to acquire light from either the Sun or Moon by vertically scanning across the object. The spectrometer uses an 800 element CCD linear array to provide continuous spectral coverage between 290 and 1030 nm. Additional aerosol information is provided by a discrete photodiode at 1550 nm. This configuration enables SAGE III to make multiple measurements of absorption features of target gaseous species and multi-wavelength measurements of broadband extinction by aerosols. These measurements are vital inputs to the global scientific community for improved understanding of climate, climate change, and human-induced ozone trends.
SAGE III – Meteor-3M is a joint mission between NASA and the Russian Space Agency (RSA). The SAGE III instrument was developed and managed by NASA Langley Research Center and was built by Ball Aerospace in Boulder, CO. Three copies were produced. One instrument is mounted on the Meteor-3M spacecraft and a second is carefully packed away awaiting a flight of opportunity. The third SAGE III instrument is scheduled to board one of NASA's first commercial Space X flights in 2014 for a ride to its new home in orbit on the International Space Station.