The Aqua Mission and the Water Cycle As mentioned earlier, the hydrologic cycle involves evaporation, transpiration, condensation, precipitation, and runoff. NASA's Aqua satellite will monitor many aspects of the role of water in the Earth's systems, and will do so at spatial and temporal scales appropriate to foster a more detailed understanding of each of the processes that contribute to the hydrologic cycle. These data and the analyses of them will nurture the development and refinement of hydrologic process models and a corresponding improvement in regional and global climate models, with a direct anticipated benefit of more-accurate weather and climate forecasts. Aqua's contributions to monitoring water in the Earth's environment will involve all six of Aqua's instruments: the Atmospheric Infrared Sounder (AIRS), the Advanced Microwave Sounding Unit (AMSU), the Humidity Sounder for Brazil (HSB), the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E), the Moderate Resolution Imaging Spectroradiometer (MODIS), and Clouds and the Earth's Radiant Energy System (CERES). The AIRS/AMSU/HSB combination will provide more-accurate space-based measurements of atmospheric temperature and water vapor than have ever been obtained before, with the highest vertical resolution to date as well. Since water vapor is the Earth's primary greenhouse gas and contributes significantly to uncertainties in projections of future global warming, it is critical to understand how it varies in the Earth system. The water in clouds will be examined with MODIS, CERES, and AIRS data; and global precipitation will be monitored with AMSR-E. The cloud data will include the height and areal coverages of clouds, the liquid water content, and the sizes of cloud droplets and ice particles, the latter sizes being important to the understanding of the optical properties of clouds and their contribution to the Earth's albedo (reflectivity). HSB and AMSR-E, both making measurements at microwave wavelengths, will have the ability to see through clouds and detect the rainfall under them, furthering the understanding of how water is cycled through the atmosphere. Frozen water in the oceans, in the form of sea ice, will be examined with both AMSR-E and MODIS data, the former allowing routine monitoring of sea ice at a coarse resolution and the latter providing greater spatial resolution but only under cloud-free conditions. Sea ice can insulate the underlying liquid water against heat loss to the often frigid overlying polar atmosphere and also reflects sunlight that would otherwise be available to warm the ocean. AMSR-E measurements will allow the routine derivation of sea ice concentrations in both polar regions, through taking advantage of the marked contrast in microwave emissions of sea ice and liquid water. This will continue, with improved resolution and accuracy, a 22-year satellite record of changes in the extent of polar ice. MODIS, with its finer resolution, will permit the identification of individual ice floes, when unobscured by clouds. AMSR-E and MODIS will also provide monitoring of snow coverage over land, another key indicator of climate change. Here too, the AMSR-E will allow routine monitoring of the snow, irrespective of cloud cover, but at a coarse spatial resolution, while MODIS will obtain data with much greater spatial detail under cloud-free conditions. As for liquid water on land, AMSR-E will provide an indication of soil moisture, which is crucial for the maintenance of land vegetation, including agricultural crops. AMSR-E's monitoring of soil moisture globally should permit, for example, the early identification of signs of drought episodes. next: The Aqua Spacecraft back: The Water Cycle and Climate Change		The Water Cycle Introduction A Multi-Phased Journey The Water Cycle and Climate Change The Aqua Mission and the Water Cycle The Aqua Spacecraft References Total precipitable water from the Advanced Microwave Sounding Unit (AMSU) aboard the NOAA 15 satellite. The AMSU instrument aboard the Aqua satellite will complement NOAA's AMSU instruments, resulting in a better understanding of the Earth’s water cycle. (Image courtesy of NOAA.)

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