Advantages and Disadvantages of Active and Passive Experiments

Shown below is a table listing some of the advantages and disadvantages to each of these types of surveys. In reading these, please note that the terms passive and active cover a wide range of geophysical survey methods. Thus, the listed advantages and disadvantages are by necessity generalizations that might not apply to any given specific survey.

Active		Passive
Advantage	Disadvantage	Advantage	Disadvantage
Better control of noise sources through control of injected signal.	Because both sources and receivers are under the surveyor's control, he must supply both. Therefore, field equipment tends to be more complex.	Surveyor need only record a naturally occurring field, therefore, he need supply only a sensor and a data recorder.	Less control of noise because source of the signal is out of the hands of the surveyor.
Because propagating fields are generally measured, active experiments usually provide better depth control over source of anomalous signal.	Field operations and logistics are generally more complex and time consuming than passive experiments.	Field operations are generally very time efficient. Thus, passive experiments can be run over wider areas in a more cost-effective manner.	Because passive fields are generally the result of integrating anomalous geological contributions over wide areas, identification of the source of an anomalous observation can be difficult.
Many different source/receiver configurations can be used allowing for a wide variety of survey designs. This allows survey designers great flexibility in customizing surveys for particular problems.	Many different source/receiver configurations can be used allowing for a wide variety of survey designs. The increase in the number of field options inevitably leads to greater survey design costs and potentially leads to increased probability of field mishaps.	One or two well-established field procedures are generally used. Contractors can provide these surveys on short notice with relatively easily quantifiable results.	One or two well-established field procedures are generally used. This limits the amount of customization that can be done for specific problems.
Once set up, active experiments are capable of producing vast quantities of data that can be used to interpret subtle details of the earth's subsurface.	The large quantity of data obtained in many active experiments can become overwhelming to process and interpret.	Interpretation of the limited set of observations can be accomplished with modest computational requirements quickly and efficiently.	The data sets collected in passive experiments are smaller than those collected in active experiments and usually do not allow for as detailed an interpretation.

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