Infrared (IR) imagery is frequently used in security/surveillance and military image processing applications. In this article we will consider the problem of outlining military naval vessels in such images. Obtaining these outlines is important for a number of applications, for instance in vessel classification.
Detecting this outline is basically a very complex image segmentation task. We will use a special neural network for this purpose. Neural networks have recently shown great promise in a wide range of image processing applications, image segmentation is no exception in this regard. The main drawback when using neural networks for this purpose is the need for substantial amounts of data in order to train the networks. This problem is of particular concern for our application due to the difficulty in obtaining IR images of military vessels.
In order to alleviate this problem we have experimented with using alternatives to true IR images for the training of the neural networks. Although such data in no way can capture the exact nature of real IR images, they do capture the nature of IR images to a degree where they contribute substantially to the training and final performance of the neural network.
Well-known detection metrics based on Johnson criteria or Target Task Performance (TTP) models were developed for land-based targets [1,2]. In this paper we investigate how (whether) we can apply these metrics to especially recognition and identification of ships at sea. Large sea targets distinguish themselves from land-based targets by their large aspect ratio, when seen broad side, and their relatively large and hot plume. We shall only address the second of these two issues here. First, however, we shall investigate how the simple Johnson approach to recognition and identification stacks up against a TTP approach. The Johnson approach has clear and simple criteria to measure the target task performance. To apply the TTP model N50 (V50) values need to be found through observer trials. We avoid these trials here but estimate the criteria based on a comparison of the models. From analysis of LWIR and MWIR recordings of a multipurpose ship running outbound and inbound tracks, we find little difference between the two metrics. As mentioned, we study the effect of the plume on task performance ranges, by considering two different estimates for the target contrast: the average contrast and the root of the squares of this contrast and the standard deviation of the contrast. We argue that the plume skews the recognition and identification ranges to much too optimistic values when the standard deviation is included. In other words, although the plume helps to detect the target, it does not help the recognition or identification task. It seems a more careful definition of the temperature contrast needs to be applied when these models are used.
Reverse saturable absorbers have shown great potential to attenuate laser radiation. Good candidate molecules and various particles have successfully been incorporated into different glass matrices, enabling the creation of self-activated filters against damaging laser radiation. Although the performance of such filters has been impressive, work is still ongoing to improve the performance in a wider range of wavelengths and pulse widths. The purpose of this tutorial is, from an optical engineering perspective, to give an understanding of the strengths and weaknesses of this class of smart materials, how relevant photophysical parameters are measured and influence system performance and comment on the pitfalls in experimental evaluation of materials. A numerical population model in combination with simple physical formulas is used to demonstrate system behavior from a performance standpoint. Geometrical reasoning shows the advantage of reverse saturable absorption over nonlinear scattering due to a fraction of scattered light being recollected by imaging system optics. The numerical population model illustrates the importance of the optical power limiting performance during the leading edge of a nanosecond pulse, which is most strongly influenced by changes in the two-photon absorption cross section and the triplet linear absorption cross section for a modeled Pt-acetylide. This tutorial not only targets optical engineers evaluating reverse saturable absorbing materials but also aims to assist researchers with a chemistry background working on optical power limiting materials. We also present photophysical data for a series of coumarins that can be useful for the determination of quantum yields and two-photon cross sections and show examples of characterization of molecules with excited triplet states.
In the past decades the Norwegian Defence Research Establishment (FFI) has recorded and characterized infrared
scenarios for several application purposes, such as infrared target and background modeling and simulation, model
validation, atmospheric propagation, and image segmentation and target detection for civilian and defence purposes.
During the last year FFI has acquired several new systems for characterization of infrared radiation properties. In total,
five new infrared cameras from IRCAM GmbH, Germany, have been acquired. These cameras cover both the longwavelength
and extended medium-wavelength infrared spectral bands. The cameras are equipped with fast rotating filter
wheels which can be used to study spectral properties and polarization effects within these wavelength bands. This
option allows the sensors to operate in user-defined spectral bands. FFI has also acquired two HyperCam sensors from
Telops Inc, Canada, covering the long-wavelength and extended medium-wavelength spectral bands, respectively. The
combination of imaging detectors and Fourier Transform spectroscopy allows simultaneous spectral and spatial
characterization of infrared scenarios. These sensors may optionally be operated as high-speed infrared cameras. A
description of the new sensors and their capabilities are presented together with some examples of results acquired by the
different sensors. In this paper we present a detailed comparison of images taken in different spectral bands, and also
compare images taken with the two types of sensors. These examples demonstrate the principles of how the new spectral
information can be used to separate certain targets from the background based on the spectral information.
A multinational field trial (SQUIRREL) was performed at the Eckernförder Bucht, in the Baltic Sea, during September 2011 to study infrared ship signature and atmospheric propagation effects close to the sea surface in a cool environment. In this paper mid-wave infrared camera recordings of ship-mounted sources are analyzed. The camera was positioned about 6 m above mean sea level. Several meteorology stations - mounted on land, on a pier and on a buoy - were used to characterize the propagation environment, while sensor heights were logged continuously. Both sub- and superrefractive conditions were studied. Measurements are compared to results from an earlier field trial performed at Chesapeake Bay, in 2006, during warm and humid atmospheric conditions. The ship-mounted sources - two calibrated blackbody sources at 200 °C and 100 °C - were used to study contrast intensity and intensity fluctuations as a function of distance. The distance to the apparent horizon is also determined. Measurement results are compared to results from the IR Boundary Layer Effects Model (IRBLEM), and good agreement is found.
Because of their strong nonlinear optical properties, Platinum(II) acetylides are investigated as potential chromophores
for optical power limiting (OPL) applications. The strong excited state absorption and efficient intersystem
crossing to the triplet states in these materials are desired properties for good OPL performance. We
recently reported on OPL and photo-physical properties of Pt(II)-acetylide chromophores in solution, modified
with thiophenyl or triazole groups. [R. Westlund et al. J. Mater. Chem. 18, 166 (2008); E. Glimsdal et al.
Proc. SPIE 6740, 67400M (2007)] The chromophores were later incorporated into poly(methyl-methacrylate)
(PMMA) glasses. A variety of doped organic solids were prepared, reaching concentrations of up to 13 wt% of
the guest molecule. Raman spectra of the doped solid devices proved that the chemical structure of the nonlinear
dyes remains intact upon the polymerization of the solid matrix. Luminescence spectra confirm that the basic
photo-physical properties (absorption, emission and inter-system crossing) observed for the solute molecules in
THF are maintained also in the solid state. In particular, the phosphorescence lifetime stays in the order of μs to
ms, just as in the oxygen evacuated liquid samples. Also, the wavelength dependence and time-dynamics of the
triplet absorption spectra of the dyes, dissolved in THF solution and dispersed in solid PMMA matrices, were
investigated and compared. Ground state UV absorption spectra between 300 and 420 nm have corresponding
broad band visible triplet-triplet absorption between 400 and 800 nm. The triplet state extinction coefficients
were determined to be in the order of 104 M-1cm-1.
The photo-physical and optical power limiting (OPL) properties of several new thiophenyl-containing arylalkynyl
Pt(II) complexes with longer arylalkynyl groups, named ATP3, ATP4, ATP6 and ATP7 were studied.
Thiophene units were introduced into the structure as an attempt to modify photo-physical properties and OPL
capability. The new compounds have their thiophene rings either close to the Pt-atom (ATP7), in the middle of
the chain (ATP3), or at the terminal end (ATP4). The measurement results were compared with those of the
earlier studied PE3 compound. ATP6 is similar to ATP4, but with methoxy groups in the arylalkynyl ligands.
Just as PE3, all thiophenyl derivatives showed large intersystem crossing capabilities and triplet phosphorescence,
thus having the potential of large nonlinear absorption and good OPL performance. All compounds
are characterized by absorption and emission spectra, quantum yield, luminescence decay (fluorescence and
phosphorescence) and two-photon absorption capabilities at 780 nm, and compared to the properties of the
PE3 compound. Also analogous triazole-containing compounds, abbreviated Z1, Z2 and Z3, were studied in
the same way, and compared to the earlier studied Pt1-G1 compound. The OPL performance of all compounds
were measured, and clamping levels of approximately 2.5 to 5 μJ pulse energy from 30 mM (ATP) and 50 mM
(triazole) concentration samples were found. All compounds possess high transmission in the visible region and
fluorescence quantum yields in the order of 10−2 (ATP) and 10−3 (triazoles).
The multi-photon absorption and optical power limiting (OPL) properties of two new thiophenyl-containing bis(ethynylaryl)bis(tributylphosphine) platinum(II) complexes (ATP1, ATP2) were studied. Thiophene units were introduced into the structure as an attempt to enhance the OPL properties. The two compounds have the thiophene rings either close to the Pt-atom (ATP1) or at the terminal ends (APT2). The measurement results were compared with those of Pt1 capped with a 2,2-bis(methylol)propionic acid (bis-MPA) dendrimer (Pt1-G1). As for Pt1-G1, both thiophenyl derivatives showed large inter-system crossing capabilities and triplet phosphorescence, indicating that these compounds have potential of enhancing the nonlinear absorption and specifically the OPL properties. The two-photon absorption cross sections of ATP1 and ATP2 was found to be in the same order of magnitude as that of Pt1-G1, i.e. between 10-20 GM, but is slightly larger for ATP1 than for ATP2. The fluorescence decay time of all compounds was found to be very short (sub nanosecond) and with quantum yields in the order of 10-3. The multi-photon induced phosphorescence was reduced with decreased pulse repetition frequency (prf) showing a population dependence of the triplet state with prf, correlating with the relatively long phosphorescence decay lifetime around 200 μs. OPL measurements at 532, 550 and 610 nm show that ATP1 has the same clamping level as Pt1-G1 at 532 nm and ATP2 has somewhat weaker OPL response than the other two.
KEYWORDS: Chromophores, Glasses, Bromine, Nonlinear optics, Polymers, Silicon, Platinum, FDA class II medical device development, Sensors, Solid state physics
Preliminary results on the optical power limiting properties of platinum(II) acetylides containing triazole units are presented. It is shown that the triazole units give a positive contribution to the limiting abilities of the platinum(II) acetylide and that this modified chromophore could have potential use in sensor protection devices. Moreover, this paper discusses how the versatile building block 2,2-bis(methylol)propionic acid (bis-MPA) can be used advantageously to functionalize nonlinear optical (NLO) platinum(II) acetylides. The bis-MPA units can be used to prepare dendritic substituents offering site isolation to the chromophore leading to improved clamping. The bis-MPA functionalization also improves the solubility of the platinum(II) acetylides in many organic solvents. The preparation of solid-state optical power limiters, where the NLO chromophore is inserted in an optically transparent matrix, is addressed. Again, the bis-MPA unit can be employed to increase the number of accessible end-groups to which matrix-compatible species can be attached. It is concluded that the hydroxy-functional platinum(II) acetylides can be modified to fit almost any matrix, organic or inorganic. Finally, depending on functionalization, it is possible to prepare doped glasses where the chromophore is either embedded in the matrix, or covalently bonded to the matrix.
The photo-physical properties of bis((4-(phenylethynyl)phenyl)ethynyl)bis(tributylphosphine) platinum(II) with 2,2-bis(methylol)propionic acid (bis-MPA) dendritic substituents were studied. The introduction of dendrimer capping was found to give rise to protection from oxygen quenching of phosphorescent states with a considerably longer decay time of the phosphorescence (0.1 -0.4 ms range) for solvents with oxygen removed or dendrimers of larger size (G2-G4) or higher concentration. Presence of oxygen reduces the phosphorescence decay time to below 1 microsecond. Two-photon induced fluorescence and z-scan of fs pulses at low pulse repetition frequency at approximately 720 nm revealed that the two-photon absorption cross-section is in the order of 0.01 cm/GW, well below the 0.34cm/GW reported by Staromlynska et al [J. Staromlynska, T. McKay and P. Wilson, J. Appl. Phys. 88, 1726 (2000)] and similar for all dendrimer complexes as well as the non-capped Pt-acetylide. Z-scans performed at high pulse repetition frequency gives an apparent two-photon absorption cross-section that is higher due to the population of excited triplet states, and the contribution from incoherent multiphoton absorption involving the triplet states.
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