|Van Zyl, Jacob|
Submitted to: IEEE Transactions on Geoscience and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2004
Publication Date: 11/1/2004
Citation: Entekhabi, D., Njoku, E., Houser, P., Spencer, M., Doiron, T., Belair, S., Crow, W., Jackson, T., Kerr, Y., Kimball, J., Koster, R., McDonald, K., O'Neill, P., Pultz, T., Running, S., Shi, J.C., Wood, E., van Zyle, J. 2004. The Hydrosphere Sate (HYDROS) mission concept: An earth system pathfinder for global mapping of soil moisture and land freeze/thaw. IEEE Transactions on Geoscience and Remote Sensing. 42:2184-2195. Interpretive Summary: HYDROS is an exploratory satellite mission that seeks to deploy the first spaceborne sensor optimally designed to globally measure surface soil moisture. Data products from HYDROS have the potential to aid a range of climatic and hydrologic applications (e.g. seasonal weather forecasting, drought monitoring, and flood forecasting) relevant to agricultural management issues. This paper provides a basic overview of the mission and includes discussion of mission instrumentation, soil moisture retrieval techniques, and scientific motivation. The mission is currently in formulation stage within NASA's Earth System Pathfinder Program and has an expected launch data sometime in 2010. USDA ARS scientists have been involved in the project since its inception and are actively working to develop agricultural applications for HYDROS data products.
Technical Abstract: The Hydrosphere State Mission (HYDROS) is a pathfinder mission in the NASA's Earth System Pathfinder Program (ESSP). The objective of the mission is to provide exploratory measurements that constitute the first global scale measurement of Earth's soil moisture and land surface freeze/thaw conditions. The mission builds on the heritage of ground-based and airborne passive and active low frequency microwave measurements that have demonstrated and validated the effectiveness of the measurements and associated algorithms for estimating the amount and phase (frozen or thawed) of surface soil moisture. The mission data will enable advances in weather and climate prediction and in mapping processes that link the water, energy and carbon cycles. The proposed HYDROS instrument is a combined radar and radiometer system operating at 1.26 GHz (with VV, HH, and HV polarizations) and 1.41 GHz (with H, V, and U polarizations) respectively. The radar and the radiometer share the aperture of a 6-meter antenna pointing at 35 degrees with respect to nadir. The lightweight deployable mesh antenna is rotated at 14.6 rpm to provide a constant look-angle scan across a swath width of 1000 km. The wide swath provides a global coverage of the Earth in 2 to 3 days with a temporal sampling less than 2 days at latitudes above 50N. The radiometer measurements allow retrieval of soil moisture in diverse (non-forested) landscapes with a resolution of 40 km. The radar measurements allow the retrieval of soil moisture at relatively high resolution (3 to 10 km). The mission includes combined radar/radiometer data products that will use the synergy of the two sensors to deliver enhanced quality soil moisture estimates. In this paper the science requirements and their traceability to the instrument design are outlined. A review of the underlying measurement physics and key instrument performance parameters are also presented.