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All-Weather Imaging

One of the big drivers for all-weather imaging comes 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, due to the lower level of scattering. 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. It also enables a ground surveillance capability from the air through cloud.

Uptake of this technology by industry has been slow, because only relatively non-aerodynamic systems with limited spatial resolutions have been demonstrated at TRL 5. Progression to higher TRL's will be possible using larger collection area imagers (better spatial resolution and radiometric sensitivity) that are conformally deployable on air platforms, as can be enabled by aperture synthesis technology.

Helicopters will be one of the first platforms to take advantage of this capability, as pilots require stereoscopic situational awareness when flying close to the ground and obstacles in visually degraded environments. These might be 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, enabling them to avoid collisions with land and have awareness of approaching water craft. Visible and infrared imagers do not have this capability due to atmospheric scattering from precipitation and absorption due to water vapour. Ship radar systems may not work well in this regime as they are generally designed for longer (out to sea) ranges any may suffer from coastline clutter when viewing towards the shore.