SOIL MOISTURE AND ITS INFERENCE VIA REMOTE SENSING

"Here the water content, c, represents also the equivalent depth of water in a whole depth of primer coat" (16:7). Data of Lindsey, Gunderson, and Riley (14:872-73) were reported in cm; and this is, in a meter of depth, equivalent to percent by volume, as Engman and Chauhan reported their data (7:194).

For years it has been obvious that hydrometric soil moisture measurement is time-consuming, labor-intensive, and not continuous; hydrologists would favor "rapid, reliable, economical, and continuous" methods (1:69). In the 1950's, researchers found a correlation among soil moisture a foot deep or more and the scattering and speed of "fast neutrons" of hydrogen; and then the neutron probe (still in use) was invented (16:66-67). While that tool is useful for supervise in real time, it is still labor-intensive, it requires gravimetric calibration data, and measurements atomic number 18 neither wide-spread nor continuous. Amer et al. reported developments of two electronic sensors (an "electrical resistivity sensor" and a "time domain reflectometer") that could be primed(p) in the field and read remotely, even continuously (1:69).

The ERS transcription did work fairly well, and its outputs were continuous; but the failure calculate was high; and if the wire leads from the sensor passed vertically from the sensor up through the soil surface--a

nearly logical expectation, water ran down the wires and gave a false variation of "moisture" content (1:82).

2. Bastiaanssen, W. G. M. Derivation of areal soil natural data from satellite measurements. In: Kienitz, G.; Milly, P. C. D.; van Genuchten, M. Th.; Rosbjerg, D.; and Shuttleworth, W. J., eds. Hydrological interactions between atmosphere, soil and vegetation. Wallingford, Oxfordshire, UK: Intern'l. Assn. of Hydrological Sciences; 1991: 95-105.

1. Amer, S. A.; Keefer, T. O.; Weltz, M. A.; Goodrich, D. C.; & Bach, L. B. Soil moisture sensors for continuous monitoring. Wat. Resources Bulletin 30: 69-84; Jan./Feb. 1994.

19. Owe, M.; & train de Griend, A. Comparison of soil moisture penetration depths for several air out soils at two microwave frequencies and implications for remote sensing. Wat. Resources Research 34: 2319-27; 1998.

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