FEATURE MAPPING
the US government declassified key camera components, Harris Corporation began modifying the military system for commercial use.
‘The Geiger-mode system is like a camera. It’s a paradigm shift in both efficiency and data quality,’ commented Mark Romano, Harris’s senior product manager. An airborne circular scanner illuminates a large area of the ground. Returning light reaches all the pixels within the photodetector’s 32 x 128 array, resulting in a 3D image
The low-power, high-sensitivity Geiger-mode The level of
resolution we can get [using lidar] relative to what we had in old topography maps is like night and day
of elevation. The system detects objects on both the fore and aft arcs of the scanned circle, with a second flight over the area providing a total of four angles from which to collect data.
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lidar was developed in the classified environment of MIT’s Lincoln Laboratory. A silicon backplane camera was designed to aggregate millions of 3D data frames resulting in a photograph-like image. With high resolution and uniform imagery, feature extraction becomes easier. This method was soon able to acquire the vast data sets from which to produce the desired resolution. ‘With a linear system, what you collect is what you get. With high-sensitivity Geiger
mode, we oversample the scene. We don’t take a measurement and just use it, like you would in a high power [linear] system,’ said Romano. Harris designed the system for topographic
applications using a standard 1,064nm (infrared) wavelength laser that produces optimal reflection in natural environments. ‘Now that the technology’s declassified, we can build the silicon camera for any wavelength,’ noted Romano. But there has to be a business case – one such possible case is undersea mapping.
Peering through water Undersea mapping is already here, with bathymetric lidar offering a new way to study coastal and deep sea topography far beneath the waves.
The US Army Corps of Engineers (USACE) collects lidar data along the coastline for government agencies responsible for monitoring aquatic vegetation, flood mitigation, sediment transport and related issues concerning coastal communities. As with landslide hazard maps, regular surveys can show how benthic and
OCTOBER 2016 l ELECTRO OPTICS 19
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3D at Depth
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