The big driver for all-weather imaging comes mainly from the aircraft industry. Atmospheric transmission in the millimetre wave band is considerably better in cloud, rain, fog, dust storms and smoke than in the visible and infrared bands under these same conditions. This benefit arises due to the lower level of scattering by atmospheric particulates. Technology exploiting this will enable low-level flying (in mountainous regions), take-off, landing (in uncontrolled areas) and runway taxiing in conditions of fog, cloud and rain. An aircraft-mounted ground surveillance millimetre wave imager could prevent the classic 'controlled flight into terrain' incidents that happen in poor weather, when flying close to the ground.
Uptake of this technology by industry has been slow, because only relatively non-aerodynamic millimetre wave imagers, with limited spatial resolutions, have been demonstrated at TRL 5. Progression to higher TRL's requires larger collection area imagers (bringing better spatial resolution and radiometric sensitivity), which due to aerodynamics is only practicable using conformally deployable sensors; these are enabled by aperture synthesis technology.
Helicopters will be one of the first platforms to take advantage of conformally deployable aperture synthesis imagers. Also, they will deliver stereoscopic situational awareness when flying close to obstacles near the ground in visually degraded environments. Such scenarios include low-level cloud and fog in temperate climates and dust storms (including haboobs and downwash induced brownouts) in dry and desert type regions.
A penetrative imaging capability through rain and coastal fog offers ships the possibility to navigate and survey regions close to the shoreline, independent of their own radars. This will assist in avoiding collisions with land and provide awareness of approaching watercraft, including rigid inflatable boats (RIB's). Visible and infrared imagers do not have this capability due to atmospheric scattering from precipitation and absorption by water vapour. Ship radar systems may not work well here either, as they are generally designed for longer (out to sea) ranges and may suffer coastline clutter when viewing towards the shore.
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