small-scale soil moisture determination with ground

36
Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion Small-scale soil moisture determination with ground-penetrating radar (GPR) Jan Igel & Holger Preetz Leibniz Institute for Applied Geophysics, Hannover, Germany 04/05/2010 EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 1 /12

Upload: others

Post on 17-Jan-2022

2 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Small-scale soil moisture determination withground-penetrating radar (GPR)

Jan Igel & Holger Preetz

Leibniz Institute for Applied Geophysics, Hannover, Germany

04/05/2010

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 1 /12

Page 2: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Moisture distribution in the topsoil

Depends on:

Weather conditions

Vegetation and rooting

Texture

Humus content

Bulk density

Aggregates

Cultivation

Example: Moisture distribution in asandy topsoil

In general, soil-moisture distribution is not homogeneous

The actual distribution is important for all non-linear processes(evapotranspiration, water flow, heat storage . . . )

small-scale variability is needed for numerical simulations

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 2 /12

Page 3: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Moisture distribution in the topsoil

Depends on:

Weather conditions

Vegetation and rooting

Texture

Humus content

Bulk density

Aggregates

Cultivation

Example: Moisture distribution in asandy topsoil

In general, soil-moisture distribution is not homogeneous

The actual distribution is important for all non-linear processes(evapotranspiration, water flow, heat storage . . . )

small-scale variability is needed for numerical simulations

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 2 /12

Page 4: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Moisture distribution in the topsoil

Depends on:

Weather conditions

Vegetation and rooting

Texture

Humus content

Bulk density

Aggregates

Cultivation

Example: Moisture distribution in asandy topsoil

In general, soil-moisture distribution is not homogeneous

The actual distribution is important for all non-linear processes(evapotranspiration, water flow, heat storage . . . )

small-scale variability is needed for numerical simulations

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 2 /12

Page 5: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Methods to determine soil moisture spatially

Point measurementsSoil sampling andgravimetric moisturedetermination

TDR (time-domainreflectometry)

+ simple and accurate− invasive and time consuming

Gap←→

Field and regional scale

Remote sensing

+ fast and suitable for large areas− limited spatial resolution− limited penetration in soil− influence of vegetation

There is a need for soil-moisture measurements on larger areaswith high spatial and temporal resolution→ Geophysical techniques: ERT, EMI, (MRT), GPR . . .GPR is a promising method and has been successfully used forsoil-moisture determination since several yearsChallenge: Optimise technique regarding high spatial resolutionand measuring progress

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 3 /12

Page 6: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Methods to determine soil moisture spatially

Point measurementsSoil sampling andgravimetric moisturedetermination

TDR (time-domainreflectometry)

+ simple and accurate− invasive and time consuming

Gap←→

Field and regional scale

Remote sensing

+ fast and suitable for large areas− limited spatial resolution− limited penetration in soil− influence of vegetation

There is a need for soil-moisture measurements on larger areaswith high spatial and temporal resolution→ Geophysical techniques: ERT, EMI, (MRT), GPR . . .GPR is a promising method and has been successfully used forsoil-moisture determination since several yearsChallenge: Optimise technique regarding high spatial resolutionand measuring progress

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 3 /12

Page 7: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Methods to determine soil moisture spatially

Point measurementsSoil sampling andgravimetric moisturedetermination

TDR (time-domainreflectometry)

+ simple and accurate− invasive and time consuming

Gap←→

Field and regional scale

Remote sensing

+ fast and suitable for large areas− limited spatial resolution− limited penetration in soil− influence of vegetation

There is a need for soil-moisture measurements on larger areaswith high spatial and temporal resolution→ Geophysical techniques: ERT, EMI, (MRT), GPR . . .GPR is a promising method and has been successfully used forsoil-moisture determination since several yearsChallenge: Optimise technique regarding high spatial resolutionand measuring progress

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 3 /12

Page 8: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Soil moisture determination by GPR

Dielectric permittivity is correlated to soil moisture: ε = f (ΘV )

free waterεr ≈ 80

bound waterεr « 80air

εr = 1

soil matrix4 ≤ εr ≤ 9

Groundwave

air

soil

T RT R

soil

groundwave

v ≈ c0√εsoil

r

Reflection at ground surface

air

soil

T RT R

soil

groundwave

R ≈ 1−√

εsoilr

1+√

εsoilr

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 4 /12

Page 9: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Soil moisture determination by GPR

Dielectric permittivity is correlated to soil moisture: ε = f (ΘV )

free waterεr ≈ 80

bound waterεr « 80air

εr = 1

soil matrix4 ≤ εr ≤ 9

Mixing modelsVolume dependent: Dobson, CRIM . . .Structure dependent: DeLoor, Maxwell-Garnet . . .Empirical: Topp or site specific

Groundwave

air

soil

T RT R

soil

groundwave

v ≈ c0√εsoil

r

Reflection at ground surface

air

soil

T RT R

soil

groundwave

R ≈ 1−√

εsoilr

1+√

εsoilr

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 4 /12

Page 10: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Soil moisture determination by GPR

Dielectric permittivity is correlated to soil moisture: ε = f (ΘV )

Groundwave

air

soil

T RT R

soil

groundwave

v ≈ c0√εsoil

r

Reflection at ground surface

air

soil

T RT R

soil

groundwave

R ≈ 1−√

εsoilr

1+√

εsoilr

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 4 /12

Page 11: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

GPR groundwave, principle

Moveout measurement (MO)

soil

air

T R

Simulated GPR data

slopegroundwave ∝ 1/vsoil

→ εsoil

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 5 /12

Page 12: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

GPR groundwave, principle

Moveout measurement (MO)

soil

air

T R

Simulated GPR data

slopegroundwave ∝ 1/vsoil

→ εsoil

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 5 /12

Page 13: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

GPR groundwave, principle

Moveout measurement (MO)

soil

air

T R

Simulated GPR data

slopegroundwave ∝ 1/vsoil

→ εsoil

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 5 /12

Page 14: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

GPR groundwave, principle

Moveout measurement (MO)

soil

air

T Rairwave

groundwave

Simulated GPR data

airwave

groundwave

v = dx/dt

slopegroundwave ∝ 1/vsoil

→ εsoil

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 5 /12

Page 15: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements

Conventional methodfirst moveout (MO) measurementthen constant-offset (CO) measurement

82 Dielectric permittivity ε

part, x > xopt). In this mode, the permittivity distribution along a profile canbe deduced rapidly. However, it can be a challenge to identify the ground wavein solely a CO measurement especially in laterally and vertically heterogeneoussoils where numerous phases will interfere.

A combination of both methods was proposed by Du (1996) and showed to bethe most appropriate to this date. First, a moveout measurement is carried outby separating the transmitter and receiver antenna. The optimal transmitter-receiver offset xopt is determined to the distance where the air and groundwave are separated and do not influence one another or interfere with reflectedwaves. Then, the profile is mapped with a CO setup as illustrated in Fig. 4.20.This ensures the correct identification of the different phases in the radargram.

-

?

x

t

aw

gw

moveout constant offset

0 x1 xopt

∝ 1/c0

∝ 1/vsoil

Figure 4.20: Schematic traveltime diagram of a ground wave measurementconsisting of a moveout measurement from x1 to xopt followed by a constantoffset measurement at x > xopt (aw: air wave, gw: ground wave).

The approach introduced above has some basic disadvantages:

� Measurements in two modes (MO or CMP and CO) have to be carried outwhich require a modification of the layout and thus are time consuming.

� Processing and interpretation of the mixed MO and CO data is timeconsuming, too. This is especially the case when 2d permittivity distri-butions are to be determined which requires a large amount of parallelprofiles.

Drawbacks:time consuming due to two measuring modes (MO and CO)velocity determination from MO sometimes difficult (heterogeneity)lateral resolution limited by optimal T–R-distance

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 6 /12

Page 16: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements

Conventional methodfirst moveout (MO) measurementthen constant-offset (CO) measurement

82 Dielectric permittivity ε

part, x > xopt). In this mode, the permittivity distribution along a profile canbe deduced rapidly. However, it can be a challenge to identify the ground wavein solely a CO measurement especially in laterally and vertically heterogeneoussoils where numerous phases will interfere.

A combination of both methods was proposed by Du (1996) and showed to bethe most appropriate to this date. First, a moveout measurement is carried outby separating the transmitter and receiver antenna. The optimal transmitter-receiver offset xopt is determined to the distance where the air and groundwave are separated and do not influence one another or interfere with reflectedwaves. Then, the profile is mapped with a CO setup as illustrated in Fig. 4.20.This ensures the correct identification of the different phases in the radargram.

-

?

x

t

aw

gw

moveout constant offset

0 x1 xopt

∝ 1/c0

∝ 1/vsoil

Figure 4.20: Schematic traveltime diagram of a ground wave measurementconsisting of a moveout measurement from x1 to xopt followed by a constantoffset measurement at x > xopt (aw: air wave, gw: ground wave).

The approach introduced above has some basic disadvantages:

� Measurements in two modes (MO or CMP and CO) have to be carried outwhich require a modification of the layout and thus are time consuming.

� Processing and interpretation of the mixed MO and CO data is timeconsuming, too. This is especially the case when 2d permittivity distri-butions are to be determined which requires a large amount of parallelprofiles.

Drawbacks:time consuming due to two measuring modes (MO and CO)velocity determination from MO sometimes difficult (heterogeneity)lateral resolution limited by optimal T–R-distance

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 6 /12

Page 17: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements: Optimised layout

Layout with 2 receivers

Benefit of new layout

only time differences have to be determinedzero crossings can be picked instead of first arrivals→ easy data processing

only constant-offset measuring mode is needed→ fast measuring progress

small distance between both receivers possible→ high spatial resolution

Result of FD-simulation andexperiment

Conventional layoutlower spatial resolutionbad fit of absolute values forsmall structures

Optimised layout (2 receivers)high spatial resolutiongood fit of absolute values

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 7 /12

Page 18: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements: Optimised layout

Layout with 2 receivers

Benefit of new layout

only time differences have to be determinedzero crossings can be picked instead of first arrivals→ easy data processing

only constant-offset measuring mode is needed→ fast measuring progress

small distance between both receivers possible→ high spatial resolution

Result of FD-simulation andexperiment

Conventional layoutlower spatial resolutionbad fit of absolute values forsmall structures

Optimised layout (2 receivers)high spatial resolutiongood fit of absolute values

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 7 /12

Page 19: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements: Optimised layout

Layout with 2 receivers

Benefit of new layout

only time differences have to be determinedzero crossings can be picked instead of first arrivals→ easy data processing

only constant-offset measuring mode is needed→ fast measuring progress

small distance between both receivers possible→ high spatial resolution

Result of FD-simulation andexperiment

Conventional layoutlower spatial resolutionbad fit of absolute values forsmall structures

Optimised layout (2 receivers)high spatial resolutiongood fit of absolute values

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 7 /12

Page 20: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements: Optimised layout

Layout with 2 receivers

Benefit of new layout

only time differences have to be determinedzero crossings can be picked instead of first arrivals→ easy data processing

only constant-offset measuring mode is needed→ fast measuring progress

small distance between both receivers possible→ high spatial resolution

Result of FD-simulation andexperiment

Conventional layoutlower spatial resolutionbad fit of absolute values forsmall structures

Optimised layout (2 receivers)high spatial resolutiongood fit of absolute values

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 7 /12

Page 21: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements: Optimised layout

Layout with 2 receivers

FD-simulation (CO)

R1

R2

v = R1R2/∆t

εr = c20/v2

Result of FD-simulation andexperiment

Conventional layoutlower spatial resolutionbad fit of absolute values forsmall structures

Optimised layout (2 receivers)high spatial resolutiongood fit of absolute values

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 7 /12

Page 22: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements: Optimised layout

FD-model: lateral resolution?

Background: dry sand (εr = 3)Anomalies: moist sand(εr = 9, separation = 10 cm)

FD-simulation:GPR analysis – input model

−1 −0.5 0 0.5 12

3

4

5

6

7

8

9

10

x [m]

ε r [ ]

model1 receiver

Result of FD-simulation andexperiment

Conventional layoutlower spatial resolutionbad fit of absolute values forsmall structures

Optimised layout (2 receivers)high spatial resolutiongood fit of absolute values

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 7 /12

Page 23: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements: Optimised layout

FD-model: lateral resolution?

Background: dry sand (εr = 3)Anomalies: moist sand(εr = 9, separation = 10 cm)

FD-simulation:GPR analysis – input model

−1 −0.5 0 0.5 12

3

4

5

6

7

8

9

10

x [m]

ε r [ ]

model1 receiver2 receivers

Result of FD-simulation andexperiment

Conventional layoutlower spatial resolutionbad fit of absolute values forsmall structures

Optimised layout (2 receivers)high spatial resolutiongood fit of absolute values

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 7 /12

Page 24: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements: Optimised layout

Sandbox setup

Background: dry sand (εr = 3)Anomaly: moist sand(εr = 5.8, width = 15 cm)

Sandbox experiment:GPR analysis – TDR data

0.25 0.5 0.75 1 1.25 1.52

3

4

5

6

7

8

x [m]

ε r [ ]

in situ1 receiver

Result of FD-simulation andexperiment

Conventional layoutlower spatial resolutionbad fit of absolute values forsmall structures

Optimised layout (2 receivers)high spatial resolutiongood fit of absolute values

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 7 /12

Page 25: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Groundwave measurements: Optimised layout

Sandbox setup

Background: dry sand (εr = 3)Anomaly: moist sand(εr = 5.8, width = 15 cm)

Sandbox experiment:GPR analysis – TDR data

0.25 0.5 0.75 1 1.25 1.52

3

4

5

6

7

8

x [m]

ε r [ ]

in situ1 receiver2 receivers

Result of FD-simulation andexperiment

Conventional layoutlower spatial resolutionbad fit of absolute values forsmall structures

Optimised layout (2 receivers)high spatial resolutiongood fit of absolute values

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 7 /12

Page 26: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Moisture by groundwave in a sandy soil (grassland)

Site 1

0 2 4 6 8 100

2

4

6

8

10

x [m]

y [m

]

ΘV [%]

0

5

10

15

anisotropy: caused by formercultivation (grassland formerlyused as tillage)

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 8 /12

Page 27: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Moisture by groundwave in a sandy soil (grassland)

Site 1

0 2 4 6 8 100

2

4

6

8

10

x [m]

y [m

]

ΘV [%]

0

5

10

15

anisotropy: caused by formercultivation (grassland formerlyused as tillage)

Density function

0 5 10 15 200

0.1

0.2

0.3

ΘV [%]

p

datafit

normal distr.ΘV = 9±2%

Variograms94 Dielectric permittivity ε

0 1 2 3 40

0.2

0.4

0.6

0.8

1

h [m]

γ [ ]

x−direction

0 1 2 3 40

0.2

0.4

0.6

0.8

1

h [m]

γ [ ]

y−direction

Figure 4.30: Statistical analysis of the permittivity distribution determinedwith the ground wave at location 2. The directional variogram is calculated inx- and y-direction and an exponential model is fitted to the curves. The rangeof the fitted models is: ax = 1.0 m and ay = 0.3 m.

also be observed in this data might be explained as the trace of a vehicle.

amax = 1.5 m, amin = 0.3 m

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 8 /12

Page 28: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Moisture by groundwave in a sandy soil (grassland)

Site 1

0 2 4 6 8 100

2

4

6

8

10

x [m]

y [m

]

ΘV [%]

0

5

10

15

anisotropy: caused by formercultivation (grassland formerlyused as tillage)

Site 2

0 2 4 6 8 100

2

4

6

8

10

x [m]

y [m

]

ΘV [%]

0

5

10

15

isotropic pattern: area formerlynot used as tillage⇒ natural variability, a = 0.35 m

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 8 /12

Page 29: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Reflection at soil surface

Measuring layout Reflection at metal, soil and soilcovered by grass

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 9 /12

Page 30: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Reflection at soil surface

Measuring layout Reflection at metal, soil and soilcovered by grass

4.3 Determining the permittivity by the coefficient of reflection 69

metal soil soil + vegetation0

2

4

6

8

10

12

14

16

t [ns

]

normalised amplitude [ ]

Figure 4.8: Radar trace of a 1 GHz horn antenna showing a wave reflectedat a metal plate, a soil surface without vegetation and a soil surface withvegetation. The amplitude is normalised to the maximum amplitude of themetal reflection.

resolution.

Therefore, the footprint6 of the used horn antenna is determined by an exper-iment. The antenna is operated into the air and an aluminium foil is placed atthe same distance to the antenna as the ground will be during the field mea-surements. The size of the foil is varied stepwise and a radar trace is recordedin each case. In Fig. 4.9 the amplitude of the reflected wave is plotted versusthe size of the metal reflector. The size is varied in the direction perpendicularto the E-field of the emitted waves (i.e. the common profile direction of the an-tenna, see Fig. 4.7) while it is hold constant and is larger than the first Fresnelzone in the other direction (i.e. perpendicular to the normal profile direction).Then, the same experiment is carried out in the other direction, i.e. the sizeof the metal reflector is varied parallel to the E-field. The amplitudes are nor-malised to the reflection of a large metal plate. The amplitude of the reflected

6The footprint is the area which is illuminated by an antenna and defines the lateralresolution (Wessel, 2006).

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 9 /12

Page 31: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Field measurement

Reflection, site 1

0 2 4 6 8 100

2

4

6

8

10

x [m]

y [m

]

ΘV [%]

0

5

10

15

Groundwave, site 1

same pattern caused by cultivationsmall differences of absolute values and variability due to differentsampling depth and lateral resolution (≈ 25 cm vs. 13 cm)

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 10 /12

Page 32: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Field measurement

Reflection, site 1

0 2 4 6 8 100

2

4

6

8

10

x [m]

y [m

]

ΘV [%]

0

5

10

15

Groundwave, site 1

0 2 4 6 8 100

2

4

6

8

10

x [m]

y [m

]

ΘV [%]

0

5

10

15

same pattern caused by cultivationsmall differences of absolute values and variability due to differentsampling depth and lateral resolution (≈ 25 cm vs. 13 cm)

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 10 /12

Page 33: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Conclusion

GPR groundwave technique has been optimised regarding lateralresolution (≈ 10 cm) and measuring progress.

Analysing reflections at the ground surface shows similar results.

GPR can be used for fast, non-invasive, high-resolutionsoil-moisture mapping and provide important input for realisticnumerical simulations.Field measuremets on different grassland-sites demonstrate that

soil moisture shows high variability with correlation length of a fewdecimetressoil moisture distribution is influenced by the former cultivation andsoil may preserve this effect for a longer time.

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 11 /12

Page 34: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Conclusion

GPR groundwave technique has been optimised regarding lateralresolution (≈ 10 cm) and measuring progress.

Analysing reflections at the ground surface shows similar results.

GPR can be used for fast, non-invasive, high-resolutionsoil-moisture mapping and provide important input for realisticnumerical simulations.Field measuremets on different grassland-sites demonstrate that

soil moisture shows high variability with correlation length of a fewdecimetressoil moisture distribution is influenced by the former cultivation andsoil may preserve this effect for a longer time.

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 11 /12

Page 35: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Open questions and outlook

Vegetation has an impact on measuring results.Depth of investigation of the groundwave is still an object ofresearchz = fct (frequency, antenna separation, ε-distribution)→ inversion might provide information on the moisturedistribution with depth and further enhance lateral resolution.

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 12 /12

Page 36: Small-scale soil moisture determination with ground

Title Motivation GPR–Moisture GPR–Groundwave GPR–Reflection Conclusion

Open questions and outlook

Vegetation has an impact on measuring results.Depth of investigation of the groundwave is still an object ofresearchz = fct (frequency, antenna separation, ε-distribution)→ inversion might provide information on the moisturedistribution with depth and further enhance lateral resolution.

EGU 2010 J. Igel & H. Preetz, LIAG Hannover Small-scale soil moisture determination with GPR 12 /12