Measurement of Moisture Content
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This document discusses methods for measuring moisture content in materials like soil, rock, and wood. Moisture content is expressed as a ratio of the mass of water to the total mass or as a volumetric ratio. It can be measured directly by drying a sample and calculating the water loss, or through various laboratory, geophysical, and remote sensing techniques. Common laboratory methods include titration and measuring mass loss after heating or freeze drying. Geophysical techniques include time-domain reflectometry and neutron probes, while satellites use microwave radiation to estimate soil moisture below vegetation canopies.
Measurement of Moisture Content
- 2. Moisture Content It is the quantity of water contained in a material. Like soil (soil moisture), rock, ceramics and wood. Moisture content is used in a wide range of scientific and technical areas. Like smart irrigation, ground water studies, soil chemistry etc. Moisture content is expressed as a ratio, which can range from 0 (completely dry) to the value of the materials' porosity at saturation. Moisture content can be given on a volumetric or mass (gravimetric) basis.
- 3. Calculation of Moisture Content Moisture content(θ) is calculated either on volumetric basis: = Volume of water and is the total volume (that is soil volume + water volume + air space). Or it is calculated on mass (gravimetric basic): Where is the mass of water and is the bulk mass.
- 4. Methods for measurement of Moisture Content 1.Direct Methods 2.Laboratory methods 3.Geophysical methods 4.Satellite remote sensing method
- 5. 1. Direct Methods Water content can be directly measured using a known volume of the material, and a drying oven. Volumetric water content, θ, is calculatedusing: Where,
- 6. 1. Direct Methods (Cont…) For materials that change in volume with water content, such as coal, the water content, u, is expressed in terms of the mass of water per unit mass of the moist specimen:
- 7. 2. Laboratory Methods These methods which determine moisture content of a sample include chemical titrations (for example the Karl Fischer titration), determining mass loss on heating (perhaps in the presence of an inert gas), or after freeze drying.
- 8. 3. Geo-physical Methods There are several geophysical methods available that can approximate in situ(in place) soil water content: 1. Time-domain reflectometry (TDR), 2. Neutron probe, 3. Frequency domain sensor, 4. Capacitance probe, 5. Amplitude domain reflectometry, 6. Electrical resistivity tomography 7. Ground penetrating radar (GPR)
- 9. 4. Satellite remote sensing Method Satellite microwave remote sensing is used to estimate soil moisture based on the large contrast between the dielectric properties of wet and dry soil. The microwave radiation is not sensitive to atmospheric variables, and can penetrate through clouds. Also, microwave signal can penetrate, to a certain extent, the vegetation canopy and retrieve information from ground surface . The data from microwave remote sensing satellite such as: WindSat, AMSR-E, RADARSAT, ERS-1-2, Metop/ASCAT are used to estimate surface soil moisture.