Brownout is the term used to describe the particulate cloud which can envelop a helicopter when it is landing in sandy terrain. Brownouts can create near-zero visibility during the last meters of descent. Typical radar solutions do not have the necessary spatial resolution in many cases. A recent article by Prophète et al. evaluates the effectiveness of terahertz imaging as an alternative. The authors envision that the brownout cloud is illuminated with a narrowband terahertz source, and the back-scattered signal is detected by a focal plane array. The paper evaluates the signal back-scattered by objects in the scene, as well as thermal noise and noise due to signal back-scattered from the sand particles in the cloud. The calculations are performed at several different frequencies, corresponding to atmospheric transmission windows between 94 GHz and 1 THz. The authors conclude that such an imaging system is feasible at frequencies below about 400 GHz, at least from the point of view of the imaging analysis. Although much of the technology needed to assemble this imaging system is still too costly, fragile, and bulky to be used in real situations, this analysis should provide further motivation for developments of the necessary components.

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