WATER HM
The document linked below is a briefing on the status of the science and technology in support of the advanced wide-swath altimeter. The document serves to collect the variety of thoughts, presentations, proposals, and publications already made regarding the potential for a joint-science hydrology and oceanography satellite mission. Both the U.S. and French space agencies, NASA and CNES, recognize the importance of WATER HM and are now investing resources toward its success. NASA and CNES have a rich, 20 year history of partnership in radar altimetry which will now be further advanced through WATER HM.
Hydrosphere Mapper
Radar altimetry has revolutionized oceanography by providing global measurements of sea surface topography. For the first time, the very broad scale circulation and heat storage of the global oceans has been sampled for a sufficient period of time leading to important discoveries. A critical drawback, however, is the 200 to 300 km spacing between orbital tracks that prevents sampling of the two-dimensional current velocity and oceanic mesoscale processes that contain 90% of the kinetic energy. Thus, Hydrosphere Mapper is a swath based altimetry instrument designed to blanket the world's oceans with elevation measurements at a greatly improved spatial resolution. The following link opens a PDF that more fully explains the mission. The document is our submission to the NRC Decadal Survey.
WATER
Okavango Flood Plain
Fresh water is essential for life, yet we have surprisingly poor knowledge of the spatial and temporal dynamics of surface water storage and discharge globally. WATER is a swath based altimetry mission designed to acquire elevations of inland water surfaces (and hence the capability to derive surface water storage and river discharge) at spatial and temporal scales necessary for answering key water cycle and water management questions of global importance. The following link opens a PDF that more fully explains the mission. The document is our submission to the NRC Decadal Survey.
Ka-Band Radar Interferometer
Both the surface water hydrology and ocean surface topography communities recognize the importance of wide-swath altimetry for its capability of acquiring high-resolution elevation measurements. The technology for WATER and HM is a Ka-band Radar INterferometer (KaRIN, 0.86 cm wavelength) that has been developed from the efforts of the Wide Swath Ocean Altimeter (WSOA; Fu, 2003; Fu and Rodriguez, 2004). KaRIN is essentially a smaller version of SRTM with two Ka-band SAR antennae at opposite ends of a 10 m boom and both antennae transmitting and receiving the emitted radar pulses along both sides of the orbital track. Look angles are limited to 4.5° providing a 120 km wide swath. The 200 MHz bandwidth achieves cross-track ground resolutions varying from about 10 m in the far swath to about 60 m in the near swath. A resolution of about 2 m in the along track direction is derived by means of synthetic aperture processing.
