Remote sensing is applied in groundwater studies to primarily sense hydraulic potential (heads) and hydraulic flux (or discharge), providing valuable data for managing and understanding groundwater resources.
Applications of Remote Sensing in Groundwater Studies
Remote sensing techniques offer several advantages for groundwater investigation, particularly in large or inaccessible areas. These applications can be broadly categorized as sensing hydraulic potential (groundwater levels) and hydraulic flux (groundwater discharge).
1. Sensing Hydraulic Potential (Groundwater Levels)
Remote sensing helps estimate groundwater levels through various sensor technologies:
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Visible Sensors: Used to map vegetation indices and land surface characteristics that may correlate with shallow groundwater levels. For example, healthy vegetation in arid regions might indicate accessible groundwater.
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Microwave Sensors: These sensors, particularly synthetic aperture radar (SAR), can detect changes in soil moisture content, which is indirectly related to groundwater levels. SAR data can penetrate clouds and vegetation to some extent, offering all-weather capabilities. InSAR (Interferometric SAR) measures land surface deformation which, under certain conditions, can be related to groundwater extraction and recharge.
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Gravity Sensors: Satellites like GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (Follow-On) measure variations in Earth's gravity field. These variations can be used to estimate changes in total water storage, including groundwater, over large areas. These are especially useful in understanding regional groundwater depletion.
2. Sensing Hydraulic Flux (Groundwater Discharge)
Remote sensing can detect areas where groundwater is discharging to the surface:
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Thermal Infrared (TIR) Sensors: These sensors measure land surface temperature. Groundwater discharge often has a different temperature than surface water or surrounding soil, making it detectable with TIR imagery. This is especially useful for identifying springs, seeps, and gaining streams (streams that receive groundwater).
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Mapping Discharge Zones: Remote sensing data combined with GIS can identify and map areas of groundwater discharge. This is particularly important for understanding groundwater-surface water interactions and managing ecosystems that depend on groundwater discharge.
3. Other Applications
Beyond hydraulic head and flux, remote sensing contributes to groundwater studies in several other ways:
- Mapping Geological Structures: Identifying faults, fractures, and other geological features that control groundwater flow.
- Land Use/Land Cover Classification: Understanding how land use affects groundwater recharge and contamination.
- Estimating Evapotranspiration: This is crucial for understanding groundwater balance and sustainable yield.
- Monitoring Groundwater Dependent Ecosystems: Assessing the health and extent of vegetation and wetlands that rely on groundwater.
| Application | Remote Sensing Technique(s) | Data Provided |
|---|---|---|
| Groundwater Level | Visible, Microwave (SAR, InSAR), Gravity (GRACE) | Soil Moisture, Land Deformation, Total Water Storage Change |
| Groundwater Discharge | Thermal Infrared (TIR) | Land Surface Temperature, Identifying Springs and Seeps |
| Geological Mapping | Multispectral, Hyperspectral, LiDAR | Identifying Faults, Fractures, Lithology |
| Land Use/Cover | Optical (e.g., Landsat, Sentinel), LiDAR | Land use types, vegetation cover, impervious surface area |
| Evapotranspiration | Thermal Infrared, Multispectral | Evapotranspiration rates |
| Ecosystem Monitoring | Multispectral, Hyperspectral, LiDAR, Thermal Infrared | Vegetation health, wetland extent, surface water temperature, indicators for areas dependent on groundwater. |
In summary, remote sensing provides a powerful suite of tools for assessing, monitoring, and managing groundwater resources. Its ability to collect data over large areas, even in remote or inaccessible regions, makes it an invaluable complement to traditional groundwater investigation methods.
