In most scientific research an important test is whether the results of an experiment can be repeated, typically repeated by another lab and research group. A result that cannot be confirmed in this way is generally viewed as invalid. This is a great test for controlled experiments where virtually identical experimental conditions may be achieved.

In Earth science research involving observations of the natural world, experimental conditions cannot be reproduced. For environmental research the standard must switch for repeatable to intercomparable – capable of being compared. Research quality observations must be capable of being compared with measurements of the same environmental variable taken at other times and/or places. This quality of intercomparability is established by following identical measurement protocols and using instruments that are calibrated by comparison to standards. Often scientists prefer the instruments to be identical or for the same instrument to be used in different times and places.

Remote sensing instruments flown on satellites are a key example of using an instrument to observe large areas of Earth for years. The calibration of the instruments must be confirmed repeatedly. The same technique applies to instruments flown on aircraft or long-duration balloons. In situ measurement systems may be moved through the environment on ships, aircraft, balloons, motor vehicles, and even by humans. In this instance the calibration also must be maintained.

By following observation protocols, using instruments with known, stable characteristics, and recalibrating when necessary, citizen scientists can take measurements that are research quality and intercomparable. In some cases scientists want these observations to be taken with identical devices. For example CoCoRaHS requires all participants to use the same rain gauge, a rain gauge that is also used in GLOBE. Data from automated weather stations is not accepted. In other cases, scientists must take into account the different characteristics of different devices when combining datasets acquired by different devices or even acquired following different protocols. An example with GLOBE is combining maximum and minimum daily air temperature data taken with digital multi-day max/min thermometers, U-tube thermometers, other max/min thermometers, and data from automated weather stations.

GLOBE provides standard observation protocols, instrument specifications, and calibration procedures that enable students and others to take intercomparable environmental measurements as citizen scientists.

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