Mapping Field-Scale Soil Moisture With L-Band Radiometer and Ground-Penetrating Radar Over Bare Soil

• Published in: IEEE transactions on geoscience and remote sensing 2011-08, Vol.49 (8), p.2863-2875
• Main Authors: Jonard, F., Weihermuller, L., Jadoon, K. Z., Schwank, M., Vereecken, H., Lambot, S.
• Format: Article
• Language: English
• Subjects: Accurate measurement; Active and passive remote sensing; Antenna measurements; Applied geophysics; Bare soils; Brightness temperatures; Calibration; Computer simulation; digital soil mapping; Earth sciences; Earth sciences & physical geography; Earth, ocean, space; Empirical model; Environmental sciences & ecology; Exact sciences and technology; Field experiment; Field-scale soil moisture; Geological surveys; Ground Penetrating Radar; Ground penetrating radar systems; Ground penetrating radars; ground-penetrating radar (GPR); Horizontal polarization; Internal geophysics; Irrigation; Irrigation patterns; L-band radiometer; L-band radiometry; Life sciences; Low frequency; Mapping; Microwave radiometry; Moisture control; Moisture determination; Monte Carlo methods; Monte Carlo Simulation; Passive remote sensing; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; Polarization; Radar; Radar measurement; Radar reflection; Radiometers; Radiometry; Reference data; Remote sensing; Research fields; RMS errors; Root-mean-square errors; Sciences de la terre & géographie physique; Sciences de l’environnement & écologie; Sciences du vivant; Soil; Soil measurements; Soil moisture; Surface properties; Surface reflections; Surface roughness; Surface soil moisture; Temperature measurement; Time domain analysis; Time Domain Reflectometry; Vertical polarization; Water content
• ISSN: 0196-2892; 1558-0644; 1558-0644
• DOI: 10.1109/TGRS.2011.2114890

Accurate estimates of surface soil moisture are essential in many research fields, including agriculture, hydrology, and meteorology. The objective of this study was to evaluate two remote-sensing methods for mapping the soil moisture of a bare soil, namely, L-band radiometry using brightness temperature and ground-penetrating radar (GPR) using surface reflection inversion. Invasive time-domain reflectometry (TDR) measurements were used as a reference. A field experiment was performed in which these three methods were used to map soil moisture after controlled heterogeneous irrigation that ensured a wide range of water content. The heterogeneous irrigation pattern was reasonably well reproduced by both remote-sensing techniques. However, significant differences in the absolute moisture values retrieved were observed. This discrepancy was attributed to different sensing depths and areas and different sensitivities to soil surface roughness. For GPR, the effect of roughness was excluded by operating at low frequencies (0.2-0.8 GHz) that were not sensitive to the field surface roughness. The root mean square (rms) error between soil moisture measured by GPR and TDR was 0.038 m 3 ·m -3 . For the radiometer, the rms error decreased from 0.062 (horizontal polarization) and 0.054 (vertical polarization) to 0.020 m 3 ·m -3 (both polarizations) after accounting for roughness using an empirical model that required calibration with reference TDR measurements. Monte Carlo simulations showed that around 20% of the reference data were required to obtain a good roughness calibration for the entire field. It was concluded that relatively accurate measurements were possible with both methods, although accounting for surface roughness was essential for radiometry.