Two-dimensional active-pixel-spectral lidar (TAPSL) is a proposed remote-sensing technique for obtaining spatially, spectrally, and temporally resolved information about terrain or other targets. Operating aboard an airborne or spaceborne platform above the Earth or a remote planet, a TAPSL system would be used to gather data on geological, biological, and chemical phenomena that manifest themselves through characteristic optical emission spectra.

Light Returning from the Target Would Be Spectrally Dispersed - in this case, along the zeroth row of an APS array. Hence, by processing the readouts from the pixels in this row at different times, one could obtain a time-resolved spectrum of the target.

A TAPSL system would include a single-frequency laser that would illuminate a target. The light returning from the target would include an elastically scattered component (the spectral component at the original laser frequency) that could be used for ranging as in conventional lidar. The return would also include inelastically scattered (Raman-shifted and fluorescent) spectral components that would be characteristic of the target material in response to excitation by the laser.

The light returning from the target would be detected by a rectangular array of active-pixel sensors (APSs) that would be sensitive to visible and near-infrared light. The APS would operate in conjunction with miniaturized electronic control, readout, and pixel-data-processing circuits. Before impinging on the APS array, the light would pass through a diffraction grating oriented to disperse the light along the rows of pixels. Consequently, the frequency or wavelength of the light received by each pixel could be identified from the position of the pixel along its row (see figure). Optionally, the system could be operated without the laser to obtain the reflected-sunlight spectrum and/or the thermal spectrum of the target.

As described thus far, the system would derive information about the relative position of the target in the manner of conventional lidar. However, if a lens were used to image the target scene onto the APS, then the position of each pixel along a column could be used to obtain spatial resolution along the corresponding axis on the target; this approach could be useful if the laser beam did not provide sufficient resolution, or if it were desired to scan the terrain in "pushbroom" fashion. Alternatively, it might be possible to vary the time gate of each pixel with position along each column to obtain additional resolution for ranging or spectral analysis.

This work was done by Quiesup Kim of Caltech for NASA's Jet Propulsion Laboratory.

NPO-20737.


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This article first appeared in the August, 2000 issue of NASA Tech Briefs Magazine.

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