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Education and the mini-DOAS

Dr. Matthew Watson has incorporated the use of the mini-DOAS into his Introduction to Remote Sensing course, in order to provide students with the opportunity to learn more about this new technology. A current Master’s student of his, Alex Matiella has written the following proposal as a project for this course:

Using DOAS for Plume Detection in the Lower Atmosphere

 

Proposal

As gaseous chemicals are emitted into our atmosphere instruments are needed to measure the amount and composition of these chemicals. One relatively new instrument currently being used for measuring gaseous plumes emitted from different sources is the Differential Optical Absorption Spectrometer (DOAS). This instrument indirectly measures the absorption of UV, visible, and near IR radiation by various gases and aerosol particles in the troposphere. As certain rays are absorbed by a plume, DOAS records which wavelengths are transmitted through the plume. Understanding the transmission of these wavelengths can give us a lot of information about the plume, like its thickness and chemical composition.

The DOAS will be used to measure the absorption of UV, visible, and near IR rays by the plume produced by the smokestack to the northwest of the Dow Environmental Sciences building. Measurements will be taken at different distances from the smokestack to evaluate the diffusion of the plume and the reliability of data taken at increasing distances from the source. The effects of the field of view (FOV) of the DOAS will also be assessed. This will help to determine the impact of taking measurements of the same point areas of the plume but from different distances.

Figure 1 shows the basic experimental setup. Measurements will be taken at intervals of 3 to 5 meters from the source, with the DOAS pointing directly vertical towards the sky to measure the absorption of rays by the plume as the distance from the source increases and the plume diffuses. Also, measurements will be taken at the same 3 to 5 meter intervals from the source with the DOAS pointing to an area of the plume that is within one distance interval from the source. These DOAS measurements will be taken within the month of April and will be taken over a series of days. The days should have clear weather with little or no cloud coverage, to minimize the chances of rain during the experiment, and a strong enough wind to carry the plume away from its source. The wind should also be at a constant speed and direction so that measurements are consistent and an artificial “back-up” or thinning of the plume does not occur. The source of the UV, visible, and near IR rays will be the sky and the DOAS will be positioned looking upwards so that it can detect the transmission of radiation through the plume.

The results produced will most likely show that DOAS does accurately measure the diffusion of the plume over a certain distance. The results of studying the different field of views of the DOAS are not certain, but they will most likely show that DOAS measurements do depend on the field of view of the DOAS relative to the plume and there is a variable of “distance sensitivity” for the instrument. It is necessary to understand the limitations of the DOAS instrument so that measurements can be taken under the most favorable conditions. Understanding these limitations can help us to collect better data and use it more efficiently.

The broader impacts of this project will be to show whether the DOAS instrument does work accurately and can be relied upon when using this instrument in the field for larger plumes, for example those produced by volcanic explosions and emissions.

 

Figure 1 -

 

meters

 

Equipment

Field Research

 

 

 


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http://www.geo.mtu.edu/volcanoes/vc_web/tools/index.html -- Revised: 10 April 2003
Copyright 2002 MTU Department of Geological Engineering and Sciences. All Rights Reserved.
Email questions about the content of this Web page to: Yvonne Branan, Lizzette Rodriguez, Alex Matiella or Matt Watson