Glossary - Agricultural Geophysics - page 392

Transmission Coeficient Given a subsurface interface separating two materials having different
properties, the transmission coefficient is the ratio of the amplitude for a radar or seismic
wave transmitted through the interface to the amplitude of the radar or seismic wave inci-
dent at the interface.
Vertical Electric Sounding Resistivity Measurement A resistivity field data collection mode
used for obtaining information on resistivity (or electrical conductivity) variations with
depth. The procedure for vertical electric sounding involves keeping the midpoint of the
resistivity array stationary, while the overall array length is successively increased. As the
electrode array is lengthened, electric current penetrates farther into the subsurface, provid-
ing a greater depth of investigation.
Wavelength The beginning to end length of a wave cycle.
Wet Aggregate Stability A measure of the degree to which soil retains its structure when wet. Wet
aggregate stability is expressed as a percentage of soil dry weight after wet sieving to the soil
dry weight before wet sieving.
Wide-Offset Reflection GPR Data Collection A ground-penetrating radar data collection mode
in which the transmitting and receiving antennas are kept at a constant but much wider
separation distance than is normal for a more typical ground-penetrating radar survey. This
type of data collection mode is commonly used for mapping near-surface soil volumetric
water content.
Wilting Point The volumetric water content level below which plants can no longer extract water
from soil. When the soil volumetric water content falls below this level, plants begin to wilt.