Earth from far above (image courtesy NASA)
Presently orbiting the Earth are a complex international array of satellites, providing services for navigation, communication, astronomy, security, and weather. Amongst these are also satellites dedicated to monitoring the environment in which we live, including our atmosphere, land and oceans. A previous post examined NASA Earth observing satellites planned for launch in the coming years. Today we look at some of the many NASA satellites that are currently in orbit around our planet.
TERRA: The heft of this satellite may be surprising, close to the size of a small bus and weighing over 11,000-lbs at launch. With this size, however, come extensive capabilities. The Terra satellite, an international mission launched in 1999, contains five separate instruments: ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer), CERES (Clouds and the Earth’s Radiant Energy System), MISR (Multi-angle Imaging SpectroRadiometer), MODIS (Moderate Resolution Imaging Spectroradiometer), and MOPITT (Measurement of Pollution in the Troposphere). Together these instruments provide a unique capacity to observe Earth’s land, ocean, atmosphere, snow, and ice, helping address questions related to climate variability and change, atmospheric composition, weather, and the water, carbon and energy cycles.
AQUA: This is a companion satellite to Terra, which, along with a collection of other existing and planned satellites, is an integral part of the multi-satellite Earth Observing System (EOS). Aqua was launched in 2002, and carries a total of six instruments: AIRS (Atmospheric Infrared Sounder), AMSU-A (Advanced Microwave Sounding Unit), HSB (Humidity Sounder for Brazil), AMSR-E (Advanced Microwave Scanning Radiometer for EOS), MODIS (Moderate Resolution Imaging Spectroradiometer), and CERES (Clouds and the Earth’s Radiant Energy System). Aqua and Terra have different orbit characteristics; hence the presence of MODIS and CERES on both satellites allows the same type of imagery to be collected at different times of the day.
TRMM (Tropical Rainfall Measuring Mission): As would be expected from its name, the mission of this satellite is focused on measuring and understanding precipitation patterns in the tropics. The mission also provides information of tropical latent heating characteristics, which will help scientists better model the global energy budget. TRMM was launched 1997 and carries five instruments: PR (Precipitation Radar), TMI (TRMM Microwave Imager), VIRS (Visible and InfraRed Scanner), CERES (Clouds and the Earth’s Radiant Energy System), and LIS (Lightning Imaging Sensor).
CloudSat: Unlike some of the other satellites, CloudSat carries a single instrument, the CPR (Cloud Profiling Radar). This instrument builds on the strong legacy of radar expertise at NASA, following the success of other instruments such as SRTM, SIR-A, SIR-B, SIR-C, QuickScat and SeaWinds. The CPR instrument on CloudSat, launched in 2006, measures the vertical profiles of clouds, providing valuable information on cloud structure and composition. Such data is a critical component in the study of climate and weather dynamics around the planet.
AURA: The four instruments aboard the Aura satellite, launched in 2004, are designed to examine Earth’s atmosphere. Measurements are targeted at better understanding trends in air quality, atmospheric composition, ozone distribution, and the climate. The instruments on Aura include: HIRDLS (High Resolution Dynamics Limb Sounder), MLS (Microwave Limb Sounder), OMI (Ozone Monitoring Instrument), and TES (Tropospheric Emission Spectrometer).
As evident from the above descriptions, a common theme among many of the Earth observing satellites is the co-location of multiple instruments on a single satellite platform. This is not only more efficient in terms of engineering, launch and management, but also facilitates the acquisition of multiple images from different types of instruments at the same time and place in orbit. Another theme is placing the same type instrument on different satellites, allowing image collection to be performed with more frequency. At the same time there are some satellites containing just one instrument with very specific measurement objectives. Together these satellites provide a multifaceted look at our planet that can be used to address a myriad of important science and societal questions.
For information on NASA’s satellite program, visit: http://science.nasa.gov/earth-science/missions/