AMSR-E Objectives

The EOS AQUA AMSR-E measures geophysical parameters supporting several global change science and monitoring efforts, including precipitation, oceanic water vapor, cloud water, near-surface wind speed, sea surface temperature, soil moisture, snow cover, and sea ice parameters. All of these measurements are critical to understanding the Earth's climate.

Water vapor is the Earth's primary greenhouse gas, essential to keeping the Earth habitable. Since it contributes the most to future projections of global warming, it is critical to understand how it varies naturally in the Earth system. The evaporation of water from the surface carries away excess heat, preventing unbearably hot temperatures in most regions. The image to the left is a monthly composite of the AMSR-E water vapor product for the month of September 2005, courtesy of Remote Sensing Systems.

Almost all of the water that evaporates eventually returns to the Earth's Surface as precipitation. In the process of precipitation formation, heat that was absorbed during evaporation is released to the atmosphere. This process provides over half of the energy needed for the global atmospheric circulation and is the prime mechanism for transferring the effects of local climate anomalies such as El Nino to other regions. Cloud water reflects sunlight back out to space, cooling the Earth. Over the ocean, the AMSR-E microwave frequencies can probe through smaller cloud particles to measure the microwave emission from the larger raindrops. Over land, the AMSR-E can measure the scattering effects of large ice particles which later melt to form raindrops. These measurements, though an indirect measure of rainfall intensity, are converted to a rain rate with the help of cloud models.

Over the ocean, AMSR-E provides sea surface temperatures (SST) through most types of cloud cover, supplementing infrared based measurements of SST that are restricted to cloud-free areas. SST fluctuations are known to have a profound impact on weather patterns across the globe, and the AMSR-E all weather capability provides a significant improvement in our ability to monitor SST's and the processes controlling them.

Ocean surface roughness is also measured by AMSR-E, which will be converted into a near-surface wind speed. These winds are one important component of how much water is evaporated from the surface of the ocean. The winds help to maintain the water vapor content of the atmosphere while precipitation continually removes it.

Soil moisture is a key state variable in land surface hydrology. It controls the proportion of rainfall that percolates, runs off, or evaporates from land. Soil moisture also enables photosynthesis in plants that use solar energy to convert carbon dioxide and water into the oxygen and food necessary for animal life on Earth. Soil moisture is important for maintaining crop and vegetation health, and its monitoring on a global basis will allow drought prone areas to be monitored for signs of drought

Sea Ice reflects sunlight away from the Earth, but it also helps the ocean to retain thermal energy by restricting evaporation and other heat transfers from the ocean surface. Monitoring of sea ice parameters, such as ice type and extent, is necessary to understand how this frozen blanket over the ocean acts to change climate through its ability to insulate the water against heat loss to the frigid atmosphere above it, and through its ability to reflect sunlight that would otherwise warm the ocean.

Snow cover over sea ice further restricts heat loss from the ocean. Similarly, snow cover over land reduces the amount of sunlight absorbed by the Earth, while also limiting the flow of heat from the ground to the atmosphere. Snow cover is also an important part of the land hydrology and provides a yearly replenishment of water resources in many regions. In much the same way as the AMSR-E can see large ice particles in the upper reaches of rain systems, it also measures the scattering effects of snow cover. These measurements are empirically related to snow cover depth and water content based upon field measurements. (photo: Extracting ice cores in a meltpond area of a multiyear floe. Courtesy of J. Maslanik, CU.)