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Estimation of soil water content using GPR and Resistivity

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  • ByNathaniel Sackey

    SupervisorDr. Kwasi Preko

  • Introduction Motivation Objectives Methodology Results Conclusions Recommendations

    Introduction Motivation Objectives Methodology Results Conclusions Recommendations

    2

  • Irrigation Farming

    Drought

    3

    Irrigation Farming

    Hydrologicalstudies

    Gully erosion

  • In view of this, GPR and Time-lapse Electricalresistivity measurements were therefore employed toassess the soil hydrological properties at KwameNkrumah University of Science and Technology(KNUST), Agric research station at Anwumaso.

    This was done for the period between 17th June and 3rdSeptember 2013.

    The methods used have been employed separately byvarious researchers. (Preko and Wilhem, 2012 ;Huisman et al, 2003; Barker and Moore, 1998).

    In view of this, GPR and Time-lapse Electricalresistivity measurements were therefore employed toassess the soil hydrological properties at KwameNkrumah University of Science and Technology(KNUST), Agric research station at Anwumaso.

    This was done for the period between 17th June and 3rdSeptember 2013.

    The methods used have been employed separately byvarious researchers. (Preko and Wilhem, 2012 ;Huisman et al, 2003; Barker and Moore, 1998).

    4

  • According to the world bank, Agricultural input to theGDP of Ghana has dropped from 41.55% in 2004 to21.96% in 2013 as a result of climate change.

    In order to mitigate the effects of climate change andalso help in the appropriate management of water inirrigation and farming in general, it is important tomonitor the soil water content for an area.

    According to the world bank, Agricultural input to theGDP of Ghana has dropped from 41.55% in 2004 to21.96% in 2013 as a result of climate change.

    In order to mitigate the effects of climate change andalso help in the appropriate management of water inirrigation and farming in general, it is important tomonitor the soil water content for an area.

    5

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  • The main objective of this research was to estimatethe volumetric water content in the near surface(0.1 m) with the Ground Penetrating Radar (GPR)technique.

    Specific objectives To investigate the spatial and temporal variability

    of soil water content over the period or work.

    To validate the GPR technique as ecient andappropriate for soil water content estimation bycomparison with time-lapse electrical resistivitymeasurements at the site.

    The main objective of this research was to estimatethe volumetric water content in the near surface(0.1 m) with the Ground Penetrating Radar (GPR)technique.

    Specific objectives To investigate the spatial and temporal variability

    of soil water content over the period or work.

    To validate the GPR technique as ecient andappropriate for soil water content estimation bycomparison with time-lapse electrical resistivitymeasurements at the site.

    7

  • For non-magnetic materials; dielectric permittivity(dielectric constant)

    = (1)

    8

    Topp et al., (1980), describes the relationship betweenrelative dielectric permittivity and the volumetric watercontent of soil as;

    Hence;(2)

    (3)

  • Ohm's law, I = V/R,

    The resistivity of a material,

    (7)

    (8)

    9

    Soil resistivity is governed by the amount of porewater.

    (8)

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  • 12 Geology of site

  • 13Profile lines at site

  • GPR MEASUREMENT

    14

  • 15

    TIME-LAPSE RESISTIVITY MEASUREMENT

  • Results from the resistivity measurementswere processed with;

    Shell script Res2dInv Res3dInv

    o

    Results from the resistivity measurementswere processed with;

    Shell script Res2dInv Res3dInv

    o

    16

    APPARENTRESISTIVITY

    INVERSION TRUE RESISTIVITY

  • The GPR data was processed using; Reflexw 4.5 Golden software Grapher 8 Golden software Surfer 11

    2D FILTER2D FILTER

    BACKGROUND REMOVALBACKGROUND REMOVAL

    The GPR data was processed using; Reflexw 4.5 Golden software Grapher 8 Golden software Surfer 11

    17

    GAINGAIN FUNCTIONGAIN FUNCTION

    1D FILTERBAND PASS BUTTERWORTHBAND PASS BUTTERWORTH SUBTRACT MEAN (DE-WOW)SUBTRACT MEAN (DE-WOW)

    STATIC CORRECTION/MUTINGSTATIC CORRECTIONSTATIC CORRECTION DYNAMIC CORRECTIONDYNAMIC CORRECTION

    BACKGROUND REMOVALBACKGROUND REMOVAL

  • 18

  • ARRIVALTIME DISTANCE(TX-RX)

    VELOCITY DIELECTRICPERMITIVITY TOPPS MODEL

    19

    WATERCONTENT

  • RESULTSRESULTS

    20

  • Results for 17th to 21st June Results for 24th to 27th June21

  • 17th June 3rd September

    22

  • Influence of precipitation on the soil water content measurements23

  • 24

  • 25Desaturation models

  • 3D resistivity on 9th July

    26

    3D resistivity on 9th July

  • 27

    3D resistivity on 26th August

  • The main objective of this research was to estimatethe volumetric water content in the near surface (0.1m) with the Ground Penetrating Radar (GPR)technique.

    The results of this work showed that, water content atthis field site is heterogeneous and ranges between 0.06m3/m3 and 0.4 m3/m3

    The main objective of this research was to estimatethe volumetric water content in the near surface (0.1m) with the Ground Penetrating Radar (GPR)technique.

    The results of this work showed that, water content atthis field site is heterogeneous and ranges between 0.06m3/m3 and 0.4 m3/m3

    28

  • To validate the GPR technique as ecient andappropriate for soil water content estimation bycomparison with time-lapse electrical resistivitymeasurements at the site.

    The results from the time lapse resistivitymeasurements were consistent with the GPR resultsand this proves that the GPR technique is effective forsoil moisture estimation.

    To validate the GPR technique as ecient andappropriate for soil water content estimation bycomparison with time-lapse electrical resistivitymeasurements at the site.

    The results from the time lapse resistivitymeasurements were consistent with the GPR resultsand this proves that the GPR technique is effective forsoil moisture estimation.

    29

  • This research has shown that soil water varies across afield depending on soil textures and that the GPRtechnique can be used by farmers to capture the spatialchanges on the field.

    Also, for researchers, the resistivity technique could berepeated with smaller electrode spacing to help resolvesmaller scale heterogeneity.

    This research has shown that soil water varies across afield depending on soil textures and that the GPRtechnique can be used by farmers to capture the spatialchanges on the field.

    Also, for researchers, the resistivity technique could berepeated with smaller electrode spacing to help resolvesmaller scale heterogeneity.

    30

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