Soil Moisture Meters. Introduction Gravimetric techniques Neutron scattering Gamma ray attenuation Electromagnetic technique including porous blocks Tensiometric techniques Microwave methods Nuclear magnetic resonance Thermal methods Time domain reflectometry Tdr Hygrometric techniques Electrolysis method Optical methods Models References. A summary of the literature overviews listed in the References section of this report is made on the various methods of measuring soil water content. Only those methods regarded as being useful by researchers are described in detail. Techniques which may become useful with further development are also mentioned. Carbon Scatter Crack. Advertising and promotional literature which was made available by manufacturers is also included. The contents of this report are not to be used in whole or in part for advertising or promotional purposes. Reference to a proprietary product or company is for specific information only and does not imply approval or recommendation of the product by the Alberta Farm Machinery Research Centre at the exclusion of others which may be suitable. Introduction. Most physical and chemical properties of soil vary with moisture content. A comparison of methods used to measure soil water content through direct, indirect and remote soil measurement. Back to Items of Interest SubTable of Contents. Laser Power, Photons, How Much Light, Beam Profile About HeNe Laser Power Ratings Any given laser be it a HeNe. UT8JtTxXVBXXXcUQpbX5/223946715/UT8JtTxXVBXXXcUQpbX5.png]];var lpix_1=pix_1.length;var p1_0= [[314' alt='Radiometry And The Detection Of Optical Radiation Pdf' title='Radiometry And The Detection Of Optical Radiation Pdf' />Specific radiative intensity is a quantity used in physics that describes electromagnetic radiation. It is a term used in much of the older scientific literature. Optics is the branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that. La eficacia luminosa de la radiacin mide la parte de energa electromagntica que se usa para iluminar y se obtiene dividiendo el flujo luminoso por el flujo radiante. International Workshop on EUV Lithography 2017 EUVL Workshop CXRO, LBNL, Berkeley, CA, USA June 1215, 2017 Workshop Proceedings Please click on links to. Measurement of soil water content is needed in every type of soil study. Hydrology, agrology, plant science and civil engineering all require soil moisture data. Soil moisture content is normally given as a dimensionless ratio of two masses or two volumes. When soil moisture content, given as a dimensionless ratio, is multiplied by 1. Where no indication of mass or volume is given, soil moisture content is normally on a mass basis. Determination of soil moisture on a volume basis involves finding mass basis figures first. Once mass basis figures are found, volume basis figures are determined using bulk density. Considering the variance in soil, some error is nearly always involved in determining bulk density. The amount of water in soil can also be given as a depth as if it were accumulated in a layer. A depth of water is typically used in irrigation. Specification of a depth of accumulated water is usually accompanied by a modifier such as, in the rooting zone. Numerous methods of obtaining soil moisture are available and include direct, indirect and remote soil moisture measurement. Direct measurements of soil water content involve removing water from a soil sample by evaporation, leaching or chemical reaction. The soil moisture content is calculated from the mass of water removed and the mass of the dry soil. Indirect methods involve measurement of some property of the soil that is affected by soil water content. Indirect methods can also measure a property of some object placed in the soil. The object placed in the soil is normally a porous absorber which comes to water equilibrium with the soil. Unfortunately, the relationships between chemical and physical soil properties and soil water content are not all well understood. The need for indirect methods for obtaining water content or indices of water content is evident when the time and labour involved in direct sampling is considered. Remote measurements include both non contact methods and measurement from a great distance. Remote sensing of soil moisture depends on the measurement of electromagnetic energy that has either been reflected or emitted from the soil surface. The variation in intensity of electromagnetic radiation with soil moisture depends on either the dielectric properties index of refraction, soil temperature or a combination of both. The property that is important depends on the wavelength region that is being considered. Soil moisture measurements from a great distance normally involve satellite systems measuring the spectral reflectance of the soil surface. Gravimetric Techniques Overview. Gravimetric measurement of soil water content is based on removal of water from the sample. Sample water is removed by evaporation, leaching or chemical reaction. Once sample water is removed, the amount of water removed from the sample is determined and used to calculate soil moisture content. Determination of water content removed is done using several methods. The simplest method to determine water content removed is by measurement of loss of weight of the sample. Sample water content can also be determined by collection of the water through distillation or absorption in a desiccant. Extraction of substances which replace sample water and measurement of a physical or chemical property of the extracting material that is affected by water content is another method. Finally, sample water content can be determined by quantitative measurement of reaction products displaced from a sample. In each of these methods the water and soil are separated and the amount of water removed is measured or inferred. Oven drying is the most widely used of all gravimetric methods. The oven dry method is the standard for the calibration of all other soil moisture determination techniques. Principle. Apparatus required for gravimetric water content measurements comes in many different forms and so exact specifications are not needed. For the oven drying method, apparatus normally includes a soil sampling device such as an auger or sampling tube. In addition, soil containers with tight fitting lids, an oven with means for controlling the temperature, a desiccator with active desiccant and a balance for weighing samples are typical of the oven drying method. Both convective and forced draft ovens are used. For precise work a vacuum oven can be of benefit. Balances used range from analytical balances to rough platform scales. The balance used is dependent on the size of the sample used and the precision of measurement desired. If soil samples are taken under conditions where evaporation losses may affect the accuracy of measurement, equipment for weighing the samples immediately or reducing evaporative loss are used. Methodology. For the oven drying method, moisture content is determined by measuring the weight of water removed. Drying the moist soil to a constant weight in a drying oven is controlled at 2. F 1. 10 5 C. Temperature of the drying oven is checked frequently to ensure adequate temperature is maintained. The time necessary to reach constant weight will depend upon the type of oven used, the size or depth of the sample and the nature of the soil. If a forced draft oven is used, samples should be dried for at least 2. Precautions should also be taken to avoid adding wet samples during the last half of the drying period. Additional time should be added if the oven is loaded heavily. The weight of soil remaining after oven drying is used as the weight of soil solids. Moisture content expressed as a percent is equal to the weight of water divided by weight of soil solids all times 1. An alternative method may be used for drying soil. Radiation drying can be used for soil water content measurements where low precision is adequate. Radiation drying uses an infrared or ordinary heat lamp. The variable drying temperature makes radiation drying less accurate than those methods using closely controlled, constant temperature drying ovens. However, the radiation drying method is rapid, requiring only a few minutes to dry the soil. Water content for stony or gravely soils, both on a mass and volume basis, can be grossly misleading. A large rock can occupy a large volume of a soil sample. Since rocks contribute to the mass and not the water capacity of the soil, errors arise.