1. a Hydrological Sciences Branch, Goddard Space Flight Center , Greenbelt, Maryland, 20771, U.S.A
2. b Department of Geography , University of Maryland , College Park, Maryland, 20742, U.S.A
3. c Science Applications Research , 4400 Forbes Boulevard, Lanham, Maryland, 20706, U.S.A
4. d Microwave Sensors Branch, Goddard Space Flight Center , Greenbelt, Maryland, 20771, U.S.A