An infrared (IR) sensor model is validated using experimentally derived peak pixel signal-to-noise ratio (SNR) versus range for detection of either an unresolved or a resolved unmanned aerial vehicle (UAV) target. The model provided estimates the time-averaged peak SNR values for the ranges used in the field collection. A mid-wave infrared (MWIR) camera and a long-wave infrared (LWIR) camera provided the measured data. Commercially available UAVs are flown along a line from the cameras to a clear sky region for background. A laser range finder measures the range at seven stopping points along the path. The data result in five ranges of unresolved target information for the MWIR camera and in four ranges for the LWIR camera. We provide details for using the data collected from the model to match the cameras used in the field collection. Also, the processing used to extract peak SNR versus range from imagery is presented.
An IR sensor model is validated using experimentally derived peak pixel SNR versus range for detection of either an unresolved or a resolved UAV target. The model provided estimated time-averaged peak SNR values for the ranges used in the field collection. A MWIR camera and a LWIR camera provided the measured data. Commercially available UAVs were flown along a line from the cameras to a clear sky region for background. A laser range finder measured the range at seven stopping points along the path. The data resulted in five ranges of unresolved target information for the MWIR camera and four ranges for the LWIR camera. This paper provides details for using the data collected from the model to match the cameras used in the field collection. Also, the processing used to extract peak SNR versus range from imagery is presented.
Longwave infrared (LWIR) and midwave infrared (MWIR) UAV signature data have been acquired and analyzed in collaboration with L3 Technologies, and we present intensity and root sum square delta T for two rotorcraft unmanned aerial vehicles (UAVs), including the popular DJI Phantom 4 and DJI Inspire, at 0-, 45-, and 90-deg aspect angles. Signature measurements are conducted in the field with clear sky, cloudy, and land backgrounds. We compare MWIR values to that of LWIR for the following criteria: aspect angle, background type, and UAV type.
KEYWORDS: Modulation transfer functions, Image quality, Video, Sensors, Motion models, Point spread functions, Systems modeling, Imaging systems, Video surveillance
As full-motion video (FMV) systems achieve smaller instantaneous fields-of-view (IFOVs), the residual line-of-sight (LOS) motion becomes significantly more influential to the overall system resolving and task performance capability. We augment the AFRL-derived Python-based open-source modeling code pyBSM to calculate distributions of motionbased modulation transfer function (MTF) based on true knowledge of line-of-sight motion. We provide a pyBSMcompatible class that can manipulate either existing or synthesized LOS motion data for frame-by-frame MTF and system performance analysis. The code is used to demonstrate the implementation using both simulated and measured LOS data and highlight discrepancies between the traditional MTF models and LOS-based MTF analysis.
KEYWORDS: Sensors, Infrared search and track, Signal to noise ratio, Long wavelength infrared, Mid-IR, Staring arrays, Target detection, Infrared sensors, Photons, Signal detection
Operationally significant infrared search and track (IRST) systems have been primarily second-generation thermal imager technology with scanned time-delay-integration (TDI) detector operation. The benefit of the scanned technology provides for large aperture, gimbal-scanned sensors with extremely wide field of regard, but with low revisit rates. Dramatic progress in large format staring arrays has provided the possibility of higher performance systems with lower complexity. These large format infrared staring arrays may be able to provide systems with higher performance (due to detector count) with less complexity (fewer gimbal scan limitations). In fact, lower performance IRST systems may satisfy operational requirements without scanning or stare-step operation in a “strap-down” architecture. The first step in a full capability staring system IRST design requires a thorough knowledge of staring array IRST performance. This knowledge includes a basic understanding of signal to noise (SNR) in both undersampled and well-sampled systems, with and without a matched filter. For undersampled systems, unresolved targets result in low SNR in both the average case and worst-case scenarios. We assess (using SNR as our primary metric) how the staring IRST system benefits from typical staring operations, such as dither and stare step. We provide a comparison of staring IRST system performance in the midwave infrared (MWIR) and longwave infrared (LWIR) with three modes of operation: basic staring (no sensor movement), dither, and stare step. In addition, we introduce a metric that allows comparison of different types of IRST systems. We use this metric to compare the performance of MWIR and LWIR as well as staring, dither, and stare-step systems. In the future, we will compare scanned systems to staring IRST systems.
A chirped fiber Bragg grating with a dispersion of 1651ps/nm is used to generate temporally stretched,
frequency chirped pulses from a passively mode locked fiber laser that generates pulses of ~1ps (FWHM)
duration at a repetition rate of 20MHz with 3.5mW average power (peak power of 175W). The use of a
chirped fiber Bragg grating enables the generation of temporally stretched pulses with low peak power so
that non-linear effects in the fiber can be avoided. A fiber based interferometeric arrangement is used for
interfering a reference signal with the reflected signal from the target to realize a coherent heterodyne
detection scheme. In the RF domain, the detected heterodyne beat frequency shifts as the target distance is
changed. A round trip target distance of 14km in air is simulated using 9.3km of optical fiber and a
resolution of less than a millimeter is observed.
Ultrashort pulse lasers based on fiber optic architecture will play a dominant role in the spread of these lasers into research and industrial applications. The principle challenge is to generate adequate pulse energy from singlemode or quasi-singlemode amplifiers which have small cross-sectional area. We demonstrate a robust, all-fiber erbium amplifier system that produces >100 μJ per pulse with 701 fs pulsewidth and M2 < 1.3. We will discuss the salient amplifier dynamics that influence the pulse generation, shaping, and propagation phenomena in state-of-the-art erbium fiber lasers. Furthermore, we show data relevant to applications and implementation of ultrashort pulse lasers.
We demonstrate a chirped-pulse amplification system generating 25 μJ compressed pulses at a center wavelength of
1552.5 nm. The seed module and the amplifier chain are all in-fiber (with a few small fiber-pigtailed free-space
components), followed by a free-space diffraction grating pulse compressor. The amplifier chain contains a pre-amplifier
and a booster whose gain fibers are 45/125 μm core/cladding-diameter, core-pumped Er-doped fibers. The pump lasers
for both amplifiers are single-mode 1480 nm Raman lasers capable of up to 8 W output. The seed module generates up
to 2 ns chirped pulses that are amplified and subsequently compressed to <800 fs duration. At a repetition rate of 50 kHz,
the 2 ns pulses from the seed module were amplified to 72 μJ, resulting in 25 μJ after pulse compression. The
corresponding peak power levels after the amplifier chain and compressor were 36 kW and 31 MW, respectively.
We show that it is possible to use of a train of counterpropagating light pulses to enhance
the coherent upconversion of intense femtosecond lasers into the extreme ultraviolet (EUV)
region of the spectrum. This all optical quasi-phase-matching uses interfering beams to
scramble the quantum phase of the generated EUV light, suppressing the contribution of
out-of-phase emission. Selective enhancement of up to 600X is observed at photon energies
of ~70 eV using argon gas and ~ 150 eV using helium gas.
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