AMSR-E is a prime example of the partnerships in place between NASA and JAXA. AMSR-E will measure geophysical parameters supporting several global change science and monitoring efforts. Of particular importance to its success is an external calibration design, which has proved suitable in other satellite microwave instrumentation for long-term monitoring of subtle changes in temperature and other variables.
Precipitation and evaporation have extremely important roles, through provision of water to the biosphere via precipitation and as an air conditioning agent that removes excess heat from the surface (via evaporation), thereby contributing toward making Earth habitable. AMSR-E will measure rain rates over both land and ocean. Over the ocean, the AMSR-E microwave frequencies can probe through smaller cloud particles to measure the microwave emission from the larger raindrops. The AMSR-E will provide sensitivity to oceanic rain rates as high as 50 mm/hr (about 2 inches per hour). Over land, AMSR-E can measure the scattering effects of large ice particles, which later melt to form raindrops. These measurements, though less direct a measure of rainfall intensity, are converted to rain rates with the help of cloud models.
Over the ocean, in addition to rain rates, AMSR-E will provide 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 AMSR-E’s all-weather capability could provide a significant improvement in our ability to monitor SSTs and the processes controlling them.
The total integrated water vapor of the atmosphere will also be measured over the ocean. This variable is important for the understanding of how water is cycled through the atmosphere. Since water vapor is the Earth’s primary greenhouse gas, and it contributes the most to future projections of global warming, it is critical to understand how it varies naturally in the Earth system. Measurements by AMSR-E of ocean surface roughness can be converted into near- surface wind speeds. These winds are an important determinant of how much water is evaporated from the surface of the ocean. Thus, the winds help to maintain the water vapor content of the atmosphere while precipitation continually removes it.
AMSR-E cloud-water estimates over the ocean will help studies of whether clouds, with their ability to reflect sunlight, increase or decrease under various conditions. This could be an important feedback mechanism that either enhances or mitigates global warming, depending on whether clouds increase or decrease with warming.
Monitoring of sea-ice parameters, such as ice concentration, type, and extent, is necessary to understand how this frozen blanket over the ocean affects the larger climate system. Sea ice has the ability to insulate the water against heat loss to the frigid atmosphere above it, and at the same time the ability to reflect sunlight that would otherwise warm the ocean. AMSR-E measurements will allow the 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.
In much the same way as AMSR-E can see large ice particles in the upper reaches of rain systems, it also measures the scattering effects of snow-cover depth. These measurements are empirically related to snow-cover depth and water content based upon field measurements. Like sea ice, snow cover has a large influence on how much sunlight is reflected from the Earth. It also acts as a blanket, keeping heat from escaping from the underlying soil and allowing deep cold air masses to develop during the winter. It further provides an important storage mechanism for water during the winter months, which then affects how much surface wetness is available for vegetation and crops in the spring. AMSR-E monitoring of snow cover will allow studies and monitoring of how snow-cover variations interplay with other climate fluctuations.
Wet soil can be identified in the AMSR-E observations if not too much vegetation is present. AMSR-E will provide the most useful satellite data yet for determination of how well low-frequency (6.9 GHz) microwave observations can be used to monitor surface wetness. Surface wetness is important for maintaining crop and vegetation health, and its monitoring on a global basis would allow drought-prone areas to be checked for signs of drought.
AMSR-E will provide unprecedented detail and accuracy in the global, all-weather measurement of these variables and thereby will allow a more-complete understanding of climate variability, ultimately enabling better climate prediction.
SOURCE: 1999 EOS Reference Handbook, 1999, pp. 98-99.