NASA Earth Observing System
Satellites are useful for more than just providing television and Internet access. The National Aeronautics and Space Administration (NASA) has used a series of artificial satellite missions, known collectively as the Earth Observing System (EOS), to learn more about the wide and wonderful planet we call home. EOS began with the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), included on the GeoEye OrbView-2 satellite. SeaWiFS was launched on an Orbital Sciences Pegasus air-launched rocket in 1997. The sensor is designed to monitor minute characteristics of the world’s oceans, such as water clarity and chlorophyll-a concentration.The first major EOS mission, however, was the Terra satellite, launched in December of 1999. This satellite followed the TRMM, Landsat 7, and QuikSCAT missions and was the first to provide detailed and ongoing information in a variety of different fields. Specifically, the satellite carries five different sensors: 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, Measurements of Pollution in the Troposphere. When the satellite ends its 15-year monitoring period, scientists will have a more complete perspective on the changes in Earth’s environments and climate. Interestingly, TERRA is a sun-synchronous satellite, meaning that it ascends/descends at the same local mean solar time at any point on the Earth’s surface.The second major EOS mission is the Aqua satellite, which was launched in May 2002 attached to a Delta II rocket. The satellite is named after the Latin word for water due to its main research focus. Aqua collects information about water in every form imaginable, including ocean evaporation, atmospheric water vapor, clouds and precipitation, sea ice, land ice, soil moisture, and snow cover. Non-water data being collected by Aqua ranges from radiative energy fluxes and land vegetation cover to phytoplankton and dissolved organic matter in the Earth’s oceans. In total, Aqua contains six scientific instruments, and has a mass of approximately 2,850 kg (6,300 lb), not counting propellant. Aqua is a main satellite in the “A Train” orbit, which also includes the CALIPSO and CloudSat satellites, as well as the French PARASOL.Aura is the most recently launched major EOS mission, put into orbit in 2004. The satellite contains four different instruments for measuring atmospheric chemistry (the air studies that its Latin name refers to). These are: HIRDLS, High Resolution Dynamics Limb Sounder, for measuring infrared radiation from a variety of sources; MLS, Microwave Limb Sounder, for measuring emissions from ozone, chlorine and trace gases in the atmosphere; OMI, Ozone Monitoring Instrument, for making ultraviolet and visible radiation maps of the ozone layer; and TES, Tropospheric Emission Spectrometer, primarily for measuring tropospheric ozone.The Earth Observing System is yet another way in which satellites have changed the way people learn about and understand their world. You can learn more information about each one at NASA’s official website.