Remote monitoring techniques

None of the foregoing methods will tell the frequency or duration of exposure of any receptor to irritant or odorous gases when each such exposure may exceed the irritation or odor response threshold for only minutes or seconds. The only way that such an exposure can be measured instrumentally is by an essentially continuous monitoring instrument, the record from which will yield not only this kind of information but also all the information required to assess hourly, daUy, monthly, and annual phenomena. Continuous monitoring techniques may be used at a particular location or involve remote sensing techniques. 

The principal requirement of a sampling system is to obtain a sample that is representative of the atmosphere at a particular place and time and that can be evaluated as a mass or volume concentration. Remote monitoring techniques are discussed in Chapter 15. The sampling system should not alter the chemical or physical characteristics of the sample in an undesirable manner. The major components of most sampling systems are an inlet manifold, an air mover, a collection medium, and a flow measurement device. 

The technique was successfully applied to monitoring at remote test sites, under computer control and data transmission to the laboratory via modem [133]. Another interesting application is the ranking of organic coatings, based on the principle that a high Rn corresponds to a good performance [134,135]. 

Xia, Y. et al. 2012. Monitoring technique of Shuping landslide with high-resolution Ladar images in Three Gorges Reservoir area, in China. Wuhan 18th China Symposium on Remote Sensing. 161-169. 

The objective ia any analytical procedure is to determine the composition of the sample (speciation) and the amounts of different species present (quantification). Spectroscopic techniques can both identify and quantify ia a single measurement. A wide range of compounds can be detected with high specificity, even ia multicomponent mixtures. Many spectroscopic methods are noninvasive, involving no sample collection, pretreatment, or contamination (see Nondestructive evaluation). Because only optical access to the sample is needed, instmments can be remotely situated for environmental and process monitoring (see Analytical METHODS Process control). Spectroscopy provides rapid real-time results, and is easily adaptable to continuous long-term monitoring. Spectra also carry information on sample conditions such as temperature and pressure. 

The cathodic protection of pipelines is best monitored by an intensive measurement technique according to Section 3.7, by an off potential survey eveiy 3 years and by remote monitoring of pipe/soil potentials. After installation of parallel pipelines, it can be ascertained by intensive measurements whether new damage of the pipe coating has occurred. These measurements provide evidence of possible external actions that can cause mechanical damage. 

Measurements either from the ground or from satellites have been a major contribution to this effort, and satellite instruments such as LIMS (Limb Infrared Monitor of the Stratosphere) on the Nimbus 7 satellite (I) in 1979 and ATMOS (Atmospheric Trace Molecular Spectroscopy instrument), a Fourier transform infrared spectrometer aboard Spacelab 3 (2) in 1987, have produced valuable data sets that still challenge our models. But these remote techniques are not always adequate for resolving photochemistry on the small scale, particularly in the lower stratosphere. In some cases, the altitude resolution provided by remote techniques has been insufficient to provide unambiguous concentrations of trace gas species at specific altitudes. Insufficient altitude resolution is a handicap particularly for those trace species with large gradients in either altitude or latitude. Often only the most abundant species can be measured. Many of the reactive trace gases, the key species in most chemical transformations, have small abundances that are difficult to detect accurately from remote platforms. 

Emission measurement techniques have in many applications proven very useful in providing an alternative to the absorption method. Emission measurements free the experimenter from the time and position restraints imposed by a celestial source and remove the complications imposed by the necessity to position a remote source in line with the gas sample of interest. One example of the application of emission measurements and their effectiveness, is their use to measure the effluents from sources such as smoke stacks (57). In this application there is usually a temperature differential which allows discrimination between the target and the ambient atmosphere. This type of measurement is most effective in monitoring target gases when they are in close proximity to the source since the target gas temperature soon becomes the same as the ambient atmosphere and their measurement becomes much more difficult if not impossible. 

Philbrick C.R. (2002). Overview of Raman lidar techniques for air pollution measurements in lidar remote sensing for industry and environmental monitoring. SPIE Proceedings, 4484, 136-150. 

Monitoring of the electrochemical potential of steel reinforcement in concrete is a well established technique for assessing the severity of corrosion and for controlling cathodic protection systems. A reference electrode is the electrochemical device used for measuring these potentials. The reference electrode is either placed on the concrete surface during the measurements or permanently embedded in the concrete in close proximity to the steel. The latter technique enables remote long-term monitoring. 

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