20
Multiscale Hydrologic Remote Sensing: Perspectives and Applications
2.4.3 coMPaRiSon with gRound-BaSed RadioMetRy
Ground-based sensors are particularly necessary for improving and validating largescale remote sensing data products. Passive microwave sensors were mainly developed for spaceborne remote sensing of soil moisture, but ground-based radiometers
were also applied at the field scale. In that respect, we compared the off-ground
GPR system with an L-band radiometer to map surface soil moisture at the field
scale (Jonard et al. 2011). The experiment was conducted on a bare agricultural
field at the Selhausen test site of the Forschungszentrum Jülich GmbH (Germany)
on July 14, 2009. GPR and L-band radiometer data were collected on a 72 × 16 m 2
experimental plot consisting of eight transects with 18 measurement points each. In
addition, TDR measurements were performed within the footprints of the GPR and
the radiometer as ground-truth information. The off-ground GPR and the L-band
radiometer JÜLBARA were mounted on the back of a truck (Figure 2.6). The Dicketype radiometer JÜLBARA was equipped with a dual-mode conical horn antenna
(aperture diameter = 68 cm, length = 61 cm). The radiometer antenna aperture was
situated about 2 m above the soil surface and directed with an observation angle of
53° relative to the vertical direction. The GPR antenna aperture was about 1.2 m
above the ground with normal incidence. The brightness temperature (T B ) measured
with the radiometer was used to derive the soil surface dielectric permittivity. T B
was measured at horizontal and vertical polarizations in the frequency range of
295800 000000 295840 000000 295880 000000 295920 000000 295960 000000 296000 000000
295800 000000
5534430 000000
5534500 000000
5534570 000000
5534640 000000
5534710 000000
295840 000000 295880 000000 295920 000000 295960 000000 296000 000000
295800 000000 295840 000000 295880 000000 295920 000000 295960 000000 296000 000000
295800 000000
5534430 000000
5534500 000000
5534570 000000
5534640 000000
5534710 000000
295840 000000 295880 000000 295920 000000 295960 000000 296000 000000
Volumetric water content (m 3 /m 3 )
Volumetric water content (m 3 /m 3 )
Off-ground GPR derived
0
25
50
75
100
Meters
STA On-ground GPR derived
Ground-truth 0-10 cm soil sampling
Ground-truth 0-10 cm soil sampling
0.03–0.06
0.06–0.09
0.09–0.12
0.12–0.15
0.15–0.18
0.18–0.21
0.21–0.24
0.24–0.27
0.27–0.30
0.30–0.33
0.33–0.36
0.36–0.39
0.39–0.42
0.42–0.45
0.45–0.48
0.48–0.51
0.51–0.54
> 0.54
Field boundary
0.03–0.06
0.06–0.09
0.09–0.12
0.12–0.15
0.15–0.18
0.18–0.21
0.21–0.24
0.24–0.27
0.27–0.30
0.30–0.33
0.33–0.36
0.36–0.39
0.39–0.42
0.42–0.45
0.45–0.48
0.48–0.51
0.51–0.54
> 0.54
Field boundary
0
25
50
75
100
Meters
N
N
(a)
(b)
5534430 000000
5534500 000000
5534570 000000
5534640 000000
5534710 000000
5534710 000000
5534640 000000
5534570 000000
5534500 000000
5534430 000000
FIGURE 2.5 Comparison between the off-ground GPR full-waveform inversion (a) and the
on-ground GPR STA approach (b) for soil moisture mapping at the field scale.
Multiscale Hydrologic Remote Sensing: Perspectives and Applications
2.4.3 coMPaRiSon with gRound-BaSed RadioMetRy
Ground-based sensors are particularly necessary for improving and validating largescale remote sensing data products. Passive microwave sensors were mainly developed for spaceborne remote sensing of soil moisture, but ground-based radiometers
were also applied at the field scale. In that respect, we compared the off-ground
GPR system with an L-band radiometer to map surface soil moisture at the field
scale (Jonard et al. 2011). The experiment was conducted on a bare agricultural
field at the Selhausen test site of the Forschungszentrum Jülich GmbH (Germany)
on July 14, 2009. GPR and L-band radiometer data were collected on a 72 × 16 m 2
experimental plot consisting of eight transects with 18 measurement points each. In
addition, TDR measurements were performed within the footprints of the GPR and
the radiometer as ground-truth information. The off-ground GPR and the L-band
radiometer JÜLBARA were mounted on the back of a truck (Figure 2.6). The Dicketype radiometer JÜLBARA was equipped with a dual-mode conical horn antenna
(aperture diameter = 68 cm, length = 61 cm). The radiometer antenna aperture was
situated about 2 m above the soil surface and directed with an observation angle of
53° relative to the vertical direction. The GPR antenna aperture was about 1.2 m
above the ground with normal incidence. The brightness temperature (T B ) measured
with the radiometer was used to derive the soil surface dielectric permittivity. T B
was measured at horizontal and vertical polarizations in the frequency range of
295800 000000 295840 000000 295880 000000 295920 000000 295960 000000 296000 000000
295800 000000
5534430 000000
5534500 000000
5534570 000000
5534640 000000
5534710 000000
295840 000000 295880 000000 295920 000000 295960 000000 296000 000000
295800 000000 295840 000000 295880 000000 295920 000000 295960 000000 296000 000000
295800 000000
5534430 000000
5534500 000000
5534570 000000
5534640 000000
5534710 000000
295840 000000 295880 000000 295920 000000 295960 000000 296000 000000
Volumetric water content (m 3 /m 3 )
Volumetric water content (m 3 /m 3 )
Off-ground GPR derived
0
25
50
75
100
Meters
STA On-ground GPR derived
Ground-truth 0-10 cm soil sampling
Ground-truth 0-10 cm soil sampling
0.03–0.06
0.06–0.09
0.09–0.12
0.12–0.15
0.15–0.18
0.18–0.21
0.21–0.24
0.24–0.27
0.27–0.30
0.30–0.33
0.33–0.36
0.36–0.39
0.39–0.42
0.42–0.45
0.45–0.48
0.48–0.51
0.51–0.54
> 0.54
Field boundary
0.03–0.06
0.06–0.09
0.09–0.12
0.12–0.15
0.15–0.18
0.18–0.21
0.21–0.24
0.24–0.27
0.27–0.30
0.30–0.33
0.33–0.36
0.36–0.39
0.39–0.42
0.42–0.45
0.45–0.48
0.48–0.51
0.51–0.54
> 0.54
Field boundary
0
25
50
75
100
Meters
N
N
(a)
(b)
5534430 000000
5534500 000000
5534570 000000
5534640 000000
5534710 000000
5534710 000000
5534640 000000
5534570 000000
5534500 000000
5534430 000000
FIGURE 2.5 Comparison between the off-ground GPR full-waveform inversion (a) and the
on-ground GPR STA approach (b) for soil moisture mapping at the field scale.