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Near-Surface Soil Water Content Measurements Using Horn Antenna Radar

Methodology and Overview

^a Dep. of Plants, Soils, and Biometeorology, Utah State Univ., Logan, UT 84322-4820, USA
^b Dep. of Civil and Environmental Engineering, Univ. of Connecticut, 261 Glenbrook Road, Unit 2037, Storrs, CT 06269-2037

View larger version (39K): [in a new window]   Fig. 1. A ground-penetrating radar (GPR) waveform of a wheat canopy overlying a wet soil. (A) Physical boundaries are denoted by dash-dot lines, diffuse boundaries of air–soil interface are shown by dashed lines, and the border of the near-field antenna range (NF) by dash-dot-dot lines. Antenna reflections of interest are (1–3), soil surface (4–6), and subsurface at (7). (B) Reflection magnitudes and distances. Vant and Vsurf denote antenna and surface voltages, respectively; tair and tp denote propagation times between the antenna and soil surface and within soil between surface and subsurface reflections, respectively. Canopy reflections (CR) are shown as small aboveground reflections in air region.

View larger version (77K): [in a new window]   Fig. 2. (A) Representative diagram of moving platform measurements, including ground truthing setup. (B) Photograph of setup at Greenville Farm.

View larger version (145K): [in a new window]   Fig. 3. (A) Representative diagram and (B) photograph of greenhouse wheat canopy measurements. GPR, ground-penetrating radar; PT, propagation time; SR, surface reflection.

View larger version (50K): [in a new window]   Fig. 4. Ground-penetrating radar and time-domain reflectometry (TDR) measurements of drying from (A) sand, (B) Millville silt loam, and (C) the sand–bentonite mixture. (D) 2-cm soil temperatures for sand (S), Millville (M), and sand–bentonite (S–B). Solid black and gray lines in B and C denote surface reflection (SR) and 2-cm TDR minimum value baselines, respectively. PT, propagation time.

View larger version (43K): [in a new window]   Fig. 5. (A) Ground-penetrating radar and time-domain reflectometry (TDR) measurements of diurnal thermodielectric effects on the sand–bentonite mixture. (B) Data logger and 2-cm soil temperatures. Red up- and blue down-pointing arrows denote 2-cm temperature maxima and minima, respectively. mbl, minimum baseline; PT, propagation time; SR, surface reflection.

View larger version (53K): [in a new window]   Fig. 6. Surface reflection (SR) and propagation time (PT) measured soil water contents with canopy development and bare soil. (A) Period from 20-35 d after planting; (B) 50-59 d; (C) drying curve after canopy removal. hc, canopy height.

View larger version (33K): [in a new window]   Fig. 7. Wheat canopy reflection development from a low canopy to maturity, with distance from the soil surface. hc, canopy height.

View larger version (17K): [in a new window]   Fig. 8. Bare soil surface reflection (SR) and propagation time (PT) vs. gravimetrically measured volumetric water contents.