We describe an optical bench design that efficiently projects broadband infrared energy from a supercontinuum (SC) source onto an extended target and collects the backscattered return. The optical system enables standoff spectral measurements of surfaces at up to 15 m away with a continuous spectral range from 3.6 to 11 μm. The goal of the optical system is to maximize energy transmission and capture under various fundamental and practical constraints imposed by the SC fiber laser source (broad spectrum, high divergence exiting the fiber), spectrometer (light collimation), detectors (étendue limits), and the overall system (size, weight, and cost). The design effort led to an all-reflective, off-axis configuration for both the transmitter and receiver, using custom-designed enhanced gold surfaces. We are able to successfully capture >90 % of the source energy and transmit it with low loss to the remote target while maintaining a nearly diffraction-limited Gaussian beam. The receiver telescope matches the detector étendue while providing uniform (±2.5 % ) off-axis signal collection over the target area to enable scanning of the SC laser spot.
Recent flight tests of the Airborne Reconfigurable Imaging System (ARIS) developed by BAE Systems have
demonstrated several key capabilities for day-night multiple target detection and tracking of maritime surface vessels.
The flight test system includes the integration of BAE Systems-developed real-time image processing algorithms with
multispectral band electro-optical (EO) (RGB)/mid-wave infrared (MWIR) sensors and a COTS turreted system.
Presented here are significant flight test results that demonstrate real-time multispectral sensor image co-registration,
geo-registration, fusion, target detection and tracking. High performance geo-pointing and line-of-sight stabilization
capabilities enable the airborne system to provide maritime domain awareness objectives for search and rescue,
persistent surveillance of moving and stationary targets, contraband traffic control through detection and tracking of
concealed vessels, and autonomous tracking of both moving and stationary vessels. Solar glint and cloud coverage false
alarms are minimized while multiple target detections and tracks are maintained. The fundamental real-time processing
methodologies used for ARIS are applied to a COTS multiple field of view system with high-resolution RGB and mid-wave
infrared (MWIR) video rate imaging. The techniques discussed for this four spectral band system can be applied to
both extended multispectral systems (greater than four spectral bands) and hyperspectral systems to further enhance
system capabilities for analogous terrestrial applications.
“Pan” or single broadband sharpening of multispectral (low spatial resolution) imagery is currently deployed on airborne and satellite systems. The challenges for spatial sharpening of hyperspectral imagery are the focus of the current study, which utilizes high spatial resolution, geo-referenced multispectral imagery available from the QuickBird satellite with low spatial resolution AVIRIS hyperspectral imagery. Performance analysis of a spectral normalization method known as the CN Spectral Sharpening (CNSS) enables correction for the mismatch in spectral radiance levels of the two input images due to differences of sensor platform altitude, date of imaging, atmospheric path and solar irradiance conditions. The BAE Systems Spectral Similarity Scale is utilized to optimize the spectral match between the unsharpened input and of selected regions of interest, combined with computing the spectral correlation difference matrix between the unsharpened input and sharpened output. Performance evaluation includes comparison of the histogram spectral means and standard deviations of selected regions of interest, combined with computing the spectral correlation difference matrix between the unsharpened and sharpened AVIRIS data. Significantly similarity is demonstrated with high spectral correlation, yet high variance change between the green and red MSI channels results in a discontinuity region of the corresponding HSI bands. Future systems incorporating collocated high spatial resolution MSI with lower resolution HSI will enable automated spatial sharpening with improved spectral accuracy.
BAE SYSTEMS has reported on a new framing camera incorporating an ultra high resolution CCD detector array comprised of 9,216 x 9,216 pixels fabricated on one silicon wafer. The detector array features a 1:2 frame-per-second readout capable of stereo imagery with Nyquist resolution of 57 lp/mm from high velocity, low altitude (V/H) airborne platforms. Flight tests demonstrated the capability of the focal plane electronics for differential image motion compensation (IMC) with Nyquist performance utilizing a focal plane shutter (FPS) to enable both nadir and significant side and forward oblique imaging angles. The impact of FPS for differential image motion compensation is evaluated with the exterior orientation calibration parameters, which include the existing shutter velocity and flight dynamics from sample mapping applications. System requirements for GPS/INS are included with the effect of vertical error and side oblique angle impact of the digital elevation map (DEM) required to create the orthophoto. Results from the differentiated "collinearity equations" which relate the image coordinates to elements of interior and exterior orientation are combined with the DEM impact to provide useful guidelines for side oblique applications. The application of real-time orthophotography is described with the implications for system requirements for side oblique orthophoto capability.
The performance characteristics of hyperspectral imaging methods for airborne reconnaissance with wide area coverage are compared for Dispersive Grating (DGS) and Fourier Transform Spectrometer (FTS) technologies. The system characteristics of field of regard ground coverage, signal-to-noise ratio, and spatial and spectral resolution are evaluated to include temporal frame time and moving platform parameters within the airborne environments. Additional trade space parameters are included for field operational examples, and real-time hyperspectral image cube processing. The comparison utilizes equivalent requirements for ground coverage rates, ground spatial resolution (GSD),s pectral range, spectral channel width, and airborne platform parameters for both the DGS and FTS approaches. Achievement of equivalent system characteristics drive the implementation and performance trades for scanning (DGS) versus step stare (FTS) field of regard ground coverage, SNR and NESR, and the subsequent trades of output data rate processing for airborne platform flight parameters of altitude, ground speed, and look angles. Comparison of existing system concepts implemented for pan-scanning with DGS and step-stare with FTS reveals fundamental differences between the concepts of operation and subsequent achievement of airborne reconnaissance objectives.