K. Peter Judd

The thermal signature of a submerged jet impacting normal to a free surface

Graphical Abstract

Passive shortwave infrared broadband and hyperspectral imaging in a maritime environment

This work offers a comparison of broadband shortwave infrared, defined as the spectral band from 0.9 to 1.7 μm, and hyperspectral shortwave infrared imagers in a marine environment under various daylight conditions. Both imagers are built around a Raytheon Vision Systems large format (1024×1280) indium-gallium-arsenide focal plane array with high dynamic range and low noise electronics. Sample imagery from a variety of objects and scenes indicates roughly the same visual performance between the two systems. However, we show that the more detailed spectral information provided by the hyperspectral system allows for object detection and discrimination. A vessel was equipped with panels coated with a variety of paints that possessed spectral differences in the 0.9 to 1.7 μm waveband. The vessel was imaged at various ranges, states of background clutter, and times of the day. Using a standard correlation receiver, it is demonstrated that image pixels containing the paint can be easily identified. During the exercise, it was also observed that both bow waves and near-field wakes from a wide variety of vessel traffic provide a spectral signature in the shortwave infrared waveband that could potentially be used for object tracking.

The thermal signature of a low Reynolds number submerged turbulent jet impacting a free surface

The thermal signature of a low Reynolds number turbulent jet impacting a free surface was investigated experimentally. Three Reynolds numbers (1000, 3000, and 4800) were investigated for a configuration in which the jet nozzle diameter and the depth of the jet beneath the free surface were fixed. A high resolution infrared detector was used to collect thermal imagery of the surface temperature field. These data were then used to examine the detailed statistical nature of the resulting coupled thermal-hydrodynamic field. The analysis included an examination of the instantaneous, mean, and fluctuating surface thermal fields. Examination of the instantaneous fields strongly suggested the existence of a turbulent core region and a weaker outer region. The existence of this inner-outer structure associated with the surface flow was confirmed by a detailed examination of the mean surface temperature fields. In addition, the outer structure of the mean surface temperature appeared to correspond well with the exi...

Automated detection of watercraft in short-wave infrared imagery

Abstract. An automated approach for detecting the presence of watercraft in a maritime environment characterized by regions of land, sea, and sky, as well as multiple targets and both water- and land-based clutter, is described. The detector correlates a wavelet model of previously acquired images with those obtained from newly acquired scenes. The resulting detection statistic outperforms two other detectors in terms of probability of detection for a given (low) false alarm rate. It is also shown how the detection statistics associated with different wavelet models can be combined in a way that offers still further improvements in performance. The approach is demonstrated to be effective in finding watercraft in previously collected short-wave infrared imagery.

A new blur kernel estimator and comparisons to state-of-the-art

This paper presents a simple, fast, and robust method to estimate the blur kernel model, support size, and its parameters directly from a blurry image. The edge profile method eliminates the need for searching the parameter space. In addition, this edge profile method is highly local and can provide a measure of asymmetry and spatial variation, which allows one to make an informed decision on whether to use a symmetric or asymmetric, spatially varying or non-varying blur kernel over an image. Furthermore, the edge profile method is relatively robust to image noise. We show how to utilize the concepts behind the statistical tools for fitting data distributions to analytically obtain an estimate of the blur kernel that incorporates blur from all sources, including factors inherent in the imaging system. Comparisons are presented of the deblurring results from this method to current common practices for real-world (VNIR, SWIR, MWIR, and active IR) imagery. The effect of image noise on this method is compared to the effect of noise on other methods.

Passive shortwave infrared technology and hyperspectral imaging for maritime applications

We present image data and discuss naval sensing applications of SWIR and Hyperspectral SWIR imaging in littoral and marine environments under various light conditions. These environments prove to be challenging for persistent surveillance applications as light levels may vary over several orders of magnitude within and from scene to scene. Additional difficulties include imaging over long water paths where marine haze and turbulence tend to degrade radiation transmission, and discrimination of low contrast objects under low-light and night imaging. Image data obtained from two separate passive sensor systems, both of which are built around an RVS large format (1280 x 1024) InGaAs FPA with high dynamic range and low noise electronics, are presented. The SWIR camera imager is equipped with a custom 300 mm focal length f/2 narrow field-of-view (6° diagonal) refractive telescope. The Hyperspectral imager has a custom selectable 900/1800 mm focal length telescope with corresponding 1.55°/0.79° field-of-view and fnumbers of 3/6 respectively. The sensor uses 1280 pixels in the spatial direction and a window of 192 are used for the spectral and operates at a nominal frame rate of 120 Hz. To assess field performance of the SWIR/Hyperspectral imagers, comparison is made to output from a scientific grade VNIR camera and two state-of-the-art low-light sensors.

Optical Signatures and Detection Strategy for a Finned Bioinspired Unmanned Undersea Vehicle

The surface expressions for a submerged finned bioinspired unmanned underwater vehicle (UUV) were examined using VNIR and longwave infrared sensors as the system maneuvered in laboratory and field environments. Laboratory experiments revealed that the eddies generated by the flapping of the finned propulsion and attitude control system initially appeared as discrete thermal boils on the water surface. As these boils evolved, expanded, and merged into one another, two parallel thermal tracks were observed. The tracks cross-linked forming a single thermal swath or footprint behind the trajectory of the vehicle. Similar thermal disruptions were observed when experiments were performed in an uncontrolled harbor environment under daytime and nighttime lighting conditions. Estimates for the background clutter, system signal, and detection statistic were generated using probabilistic models to demonstrate the feasibility of extracting signals from complex environments in both laboratory and harbor experiments. Performance of the detection model was presented in the form of receiver operating characteristic curves. Results clearly demonstrate that we can achieve > 99% probability of detecting the presence of the UUV with a very low probability of false alarm (< 0.005%) in a real harbor environment, where we estimate

Analysis of Infrared Radiation at an Air-Water Interface

\text{signal-to-noise ratio}=21.5

Horizontal atmospheric turbulence, beam propagation, and modeling

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Pulsed holographic system for imaging through spatially extended scattering media

The problem of determining the strength of the infrared radiation from an air-water interface has been addressed analytically. The approach taken here is to express the Planck spectrum as a linear function of the temperature, an approximation valid for small variations of the temperature from the surface temperature, and to assume a linear temperature profile across the thermal boundary layer. The main result shows that the deviation of the surface radiation intensity from the Planck spectrum due solely to thermal stratification, is linearly proportional to the temperature change across the thermal boundary layer and the optical depth, but is inversely proportional to the thermal boundary layer thickness. This signal was shown to be about one order of magnitude greater than the noise level expected from modern CCD IR sensors at a wavelength of about 3.8 microns. It is suggested that controlled laboratory experiments be conducted to verify these theoretical estimates.