The rapid rate at which the trace composition of Earth's atmosphere has changed over the past few decades has resulted in a dramatic increase in atmospheric research. In particular, a large effort has been directed towards measurement of atmospheric trace-gases. trace-gases are known to play a disproportionately large role in atmospheric chemistry and climate and yet, because of their sparse abundance, can be very difficult to measure. Knowledge of these trace-species is essential for understanding and quantifying these atmospheric changes. It is also important for the proper validation and improvement of chemical models which can, in turn, be used to predict the future state of the atmosphere. There are two main observation techniques in the measurement of trace-gases: in-situ and remote sensing. In-situ techniques make observation at the location of the instrument. In the stratosphere, measurements can only be made from mobile platforms which severely limits their ability to make long-term observations.
Remote sensing techniques, by measuring the intensity of light at many wavelengths, interpret the results of the interaction of electromagnetic waves with the atmosphere through absorption, emissions, or scattering. Remote measurements utilize the fine structure of the molecular absorption lines, either electronic, vibrational, or rotational. The spectral regions utilized include the UV, visible, infrared, and microwave. A larger number of techniques and instruments exist which are able to measure many of the different trace-species throughout the homosphere. Each technique offers advantages and disadvantages including complexity of the instrument, complexity