Short wave infrared (SWIR) sensors are becoming more common in DoD imaging systems because of their haze penetration capabilities and spectral properties of materials in this waveband. Typical SWIR systems have provided either full motion video (FMV) with framing panchromatic systems or multi-spectral or hyperspectral imagery with line-scanning systems. The system described here bridges these modalities, providing FMV with nine discrete spectral bands. Nine pixel sized SWIR filters are arranged in a repeating 3x3 pattern and mounted on top of a COTS, 2D staring focal plane array (FPA). We characterize the spectral response of the filter and integrated sensor. Spot-scan measurements and data collected with this camera using narrow band sources reveals crosstalk induced nonlinearity in the sensor response. We demonstrate a simple approach to reduce the impact of this nonlinearity on collected imagery.
The single photon sensitivity of Geiger-mode avalanche photo diodes (GmAPDs) has facilitated the development of LADAR systems that operate at longer stand-off distances, require lower laser pulse powers and are capable of imaging through a partial obscuration. In this paper, we describe a GmAPD LADAR system which operates at the eye-safe wavelength of 1541 nm. The longer wavelength should enhance system covertness and improve haze penetration compared to systems using 1064 nm lasers. The system is comprised of a COTS 1541 nm erbium fiber laser producing 4 ns pulses at 80 kHz to 450 kHz and a COTS camera with a focal plane of 32x32 InGaAs GmAPDs band-gap optimized for 1550 nm. Laboratory characterization methodology and results are discussed. We show that accurate modeling of the system response, allows us to achieve a depth resolution which is limited by the width of the camera’s time bin (.25 ns or 1.5 inches) rather than by the duration of the laser pulse (4 ns or 2 ft.). In the presence of obscuration, the depth discrimination is degraded to 6 inches but is still significantly better than that dictated by the laser pulse duration. We conclude with a discussion of future work.
Short wave infrared (SWIR) spectral imaging systems are vital for Intelligence, Surveillance, and Reconnaissance (ISR)
applications because of their abilities to autonomously detect targets and classify materials. Typically the spectral
imagers are incapable of providing Full Motion Video (FMV) because of their reliance on line scanning. We enable
FMV capability for a SWIR multi-spectral camera by creating a repeating pattern of 3x3 spectral filters on a staring focal
plane array (FPA). In this paper we present the imagery from an FMV SWIR camera with nine discrete bands and
discuss image processing algorithms necessary for its operation. The main task of image processing in this case is
demosaicking of the spectral bands i.e. reconstructing full spectral images with original FPA resolution from spatially
subsampled and incomplete spectral data acquired with the choice of filter array pattern. To the best of author's
knowledge, the demosaicking algorithms for nine or more equally sampled bands have not been reported before.
Moreover all existing algorithms developed for demosaicking visible color filter arrays with less than nine colors assume
either certain relationship between the visible colors, which are not valid for SWIR imaging, or presence of one color
band with higher sampling rate compared to the rest of the bands, which does not conform to our spectral filter pattern.
We will discuss and present results for two novel approaches to demosaicking: interpolation using multi-band edge
information and application of multi-frame super-resolution to a single frame resolution enhancement of multi-spectral
spatially multiplexed images.