Schott J.R.,Rochester Institute of Technology |
Hook S.J.,Jet Propulsion Laboratory |
Barsi J.A.,Science Systems And Applications Inc. |
Markham B.L.,NASA |
And 3 more authors.
Remote Sensing of Environment | Year: 2012
Landsat's continuing record of the thermal state of the earth's surface represents the only long term (1982 to the present) global record with spatial scales appropriate for human scale studies (i.e., tens of meters). Temperature drives many of the physical and biological processes that impact the global and local environment. As our knowledge of, and interest in, the role of temperature on these processes have grown, the value of Landsat data to monitor trends and process has also grown. The value of the Landsat thermal data archive will continue to grow as we develop more effective ways to study the long term processes and trends affecting the planet. However, in order to take proper advantage of the thermal data, we need to be able to convert the data to surface temperatures. A critical step in this process is to have the entire archive completely and consistently calibrated into absolute radiance so that it can be atmospherically compensated to surface leaving radiance and then to surface radiometric temperature. This paper addresses the methods and procedures that have been used to perform the radiometric calibration of the earliest sizable thermal data set in the archive (Landsat 4 data). The completion of this effort along with the updated calibration of the earlier (1985-1999) Landsat 5 data, also reported here, concludes a comprehensive calibration of the Landsat thermal archive of data from 1982 to the present. © 2012 Elsevier Inc.
Unified characterization of imaging sensors from visible through longwave IR The use of minimum resolvable contrast measurements enables a uniform approach to characterizing imaging sensor performance in the visible, near-IR, and shortwave IR spectral ranges. Modern reconnaissance strategies are based on gathering information from sensors that operate in several spectral bands. Besides the well-known atmospheric windows at the visible (VIS), medium-wave IR, and longwave-IR (LWIR) wavelengths, today's detectors can also operate in the 1–1.7μm window known as shortwave IR (SWIR). SWIR cameras are especially useful in the hazy or misty atmospheric conditions typical of a maritime environment. For optimum application of SWIR cameras, as well as detectors in other bands, it would be useful to have a single, uniform method of characterizing the various sensors. One way to provide such characterization is to use minimum resolvable contrast (MRC) measurements. MRC is a measure of a system's sensitivity and its ability to resolve data. It was pioneered by John Johnson in the late 1950s when he first described the probability of detecting an object as dependent on the object's effective resolution.1 This intuitive idea showed that the probability of locating a target increases with the number of resolvable cycles across that target. Johnson's analysis was initially used to assist the design of image intensifier tubes, which increase the intensity of light in optical systems where there is limited light available. Later—with the growing importance of day sight (surveillance) cameras—Johnson's work was revived by developers who used MRC measurements to assess electro- optical systems. SWIR imaging makes use of the radiation reflected by observed objects in the same way that visible imaging does. It is therefore possible to use MRC methods to characterize SWIR imaging.2 We have employed MRC measurements to determine the ability of a camera system to resolve detail contrast in the visible spectrum in relation to range and luminance. The system (optics, detector, electronics, display, and the observer's eye) captures a collimated USAF 1951 resolution test chart in front of an adjustable light source (see Figure 1). The USAF target is a widely accepted test pattern created by the US Air Force, and consists of groups of three bars with different dimensions, from large to small. The imager's resolving power is defined as the largest bar in the pattern that it cannot discern. We used a sequence of USAF targets—which had different contrast values in the bar pattern structure—to establish an MRC curve as a function of spatial frequency. We input the recorded values into visual range model (VRM) software,3 which calculated the ranges of the camera system. The output is presented as a graph that shows contrast to spatial frequency at a given luminance. Figure 1. Setup used for measuring minimum resolvable contrast (MRC). Setup used for measuring minimum resolvable contrast (MRC). 3 The targets are mounted in front of a light source with specified luminance. The outcoming light is collimated by a parabolic mirror and directed into the aperture of the camera under test. The camera is fixed on a rotatable arm to allow measurements under different angles of incidence. To take experimental MRC measurements, we used a light bulb with a temperature of 3000K as the visible light source. This temperature is considerably lower than that of our key visible light source—the Sun—which radiates with a source temperature of 5777K and emits a different spectrum (see Figure 2). Thus, to compare the amount of light in the VIS band with that in the SWIR and near-IR (NIR) bands, we evaluated correction factors for NIR and SWIR from the calculated integrals of the light distribution in the corresponding bands. We realized our measurements using the patterns taken by two different cameras (see Table 1). The first camera had one HD color sensor with a switchable optical filter, which enables VIS and NIR imaging. The second realizes simultaneous imaging on two image sensors, and thus enables recording of VIS and SWIR images. The results of the MRC values are shown in Figure 3.4 We used these values to make a range of calculations in VRM3 for a maritime atmosphere. The achievable ranges are shown in Figure 4. Figure 2. Relative spectral emittance (I) in the visible (VIS), near-IR (NIR), and shortwave IR (SWIR) wavelength bands in sunlight and under a halogen bulb. Figure 3. Measured MRC values. The diagram shows the contrast of targets of Table 1 as a function of the spatial resolution for the spectral ranges VIS, NIR, and SWIR. Notably, the spatial resolution of the SWIR sensor is three times lower than the other two. Figure 4. Calculated ranges for detection (D), recognition (R), and identification (I) in the VIS, NIR, and SWIR wavelengths based on the measured MRC data from Table Calculated ranges for detection (D), recognition (R), and identification (I) in the VIS, NIR, and SWIR wavelengths based on the measured MRC data from Table 1 In summary, we have described a single approach based on MRC measurements to characterize the performance of imaging sensors in the VIS, NIR, and SWIR spectral ranges. We demonstrated measurement of MRC for all three types of sensors, showing that this approach has potential for use in real-world devices. Our method would enable a reliable base from which to make a range of calculations under all kinds of atmospheric conditions. In future work, we will apply MRC methods to assess commercial camera devices and to create consistent assessment parameters for multi-camera observation platforms, such as those in submarines and tank periscopes. Airbus DS Optronics Martin Gerken is a project manager who holds responsibility for the development of a day sight zoom camera for operation in spectral ranges from VIS to SWIR. He holds a doctor's degree in nuclear physics with synchrotron radiation from the University of Hamburg. Harry Schlemmer obtained a diploma in physics from the Technical University of Hannover in 1978, and completed a PhD thesis on investigations of two-photon amplification in coupled laser systems. He was group manager for spectral analysis at Carl Zeiss, Oberkochen, from 1981 until 1992, and was later manager of the optical technology research and development department. Since 2008 he has been principal scientist for optical technology and systems design at Airbus DS Optronics. Mario Münzberg is director of the Imaging Devices Department, where he is responsible for the cross-functional development of all imaging modules and devices that are sensitive in the VIS, near-IR, SWIR, and IR spectral bands. He holds a doctor's degree in physics from the Institute of Applied Physics in Erlangen, Germany. 2. M. Gerken, H. Schlemmer, H. Haan, C. Siemens, M. Münzberg, Characterization of SWIR cameras by MRC measurements, Proc. SPIE 9071, p. 907110, 2014. doi:10.1117/12.2052928 4. M. Gerken, H. Schlemmer, M. Mnzberg, Unified characterization of imaging sensors from visible through longwave IR, Proc. SPIE 9820, p. 98200G, 2016. doi:10.1117/12.2224182
Macro to nanoscale imaging using planar lenses at visible wavelengths A novel fabrication process from the Capasso lab develops highly efficient planar metalenses that allow for diffraction-limited focusing, unprecedented imaging quality, and the ability to resolve chirality. The bulky nature of optical components has long hindered their convenient integration into our daily lives. Digital single-lens reflex (DSLR) cameras, for example, require multiple sets of bulky lenses that must be interchanged depending on the desired imaging parameters. Analogous to the miniaturization of silicon chips that has revolutionized electronic devices over the past few decades, lightweight and planar optical components are key factors for enabling the development of easy-to-carry or wearable devices. Traditionally, optical devices shape the wavefront of light via propagation through a bulky medium, like a lens. Furthermore, to improve the image quality or extract additional information (e.g., polarization), optical components must be cascaded, resulting in heavy and bulky systems. In this scenario, metasurfaces1–4—which enable wavefronts to be controlled without requiring volumetric propagation—open up a new frontier in optics. Multifunctional, high-performance metasurfaces have been reported, but the materials that are commonly used (i.e., noble metals5 or silicon6, 7) are lossy in the visible spectrum. As a result, practical demonstrations in this region are lacking. We have recently developed a fabrication approach based on the atomic-layer deposition (ALD) of titanium dioxide (TiO ), yielding high-aspect-ratio nanostructures with negligible material and scattering losses.8 With this TiO -based metasurface platform,8–11 we have fabricated metalenses that operate at visible wavelengths with unprecedented imaging quality.9 Our metalenses are also capable of resolving chirality, thereby opening up potential applications in drug development, where distinguishing isomeric (i.e., chiral) compounds is essential.10 The building block of our metalenses—a TiO nanofin, deposited on a glass substrate—is shown in Figure 1(A) and (B). The phase of circularly polarized incident light is controlled by means of the Pancharatnam-Berry phase12, 13 via rotation of the nanofins: see Figure 1(B). The metalens operates in transmission mode and focuses collimated incident light onto a spot: see Figure 1(C).9 We fabricated three distinct metalenses, with numerical apertures (NAs) of 0.8, to operate at wavelengths of 660, 532, and 405nm (i.e., red, green, and blue light, respectively). A scanning-electron-microscope image of a fabricated metalens is shown in Figure 1(D), and the measured focal spots are shown in Figure 2(A–C). Corresponding vertical cuts of these focal spots—see Figure 2(D–F)—reveal symmetric and subwavelength-focusing features. Full width at half-maximums (FWHMs) of the focal spots for these metalenses are 280, 375, and 450nm, respectively. We also achieved measured efficiencies of 86, 73, and 66% at the three respective wavelengths. Figure 1. Metalens design and fabrication. ) nanofin on a glass substrate. Phase is imparted via the rotation of each nanofin by the angle θ. (C) The metalens, composed of arrays of rotated nanofins, focuses collimated incident light to a spot. (D) Scanning electron microscope (SEM) image of a portion of a metalens. Scale bar: 600nm. Metalens design and fabrication. 9 (A) Side view and (B) top view of our metalens building block, a titanium dioxide (TiO) nanofin on a glass substrate. Phase is imparted via the rotation of each nanofin by the angle θ. (C) The metalens, composed of arrays of rotated nanofins, focuses collimated incident light to a spot. (D) Scanning electron microscope (SEM) image of a portion of a metalens. Scale bar: 600nm. Figure 2. Diffraction-limited focal-spot intensity profiles for three metalenses with design wavelengths of (A) 660, (B) 532, and (C) 405nm, Diffraction-limited focal-spot intensity profiles for three metalenses with design wavelengths of (A) 660, (B) 532, and (C) 405nm, 9 and (D–F) the corresponding full width at half-maximum (450, 375, and 280nm, respectively). All metalenses have the same diameter (240μm) and focal length (90μm), resulting in a numerical aperture (NA) of 0.8. To demonstrate the imaging capability of our design, we fabricated a metalens with a diameter of 2mm and focal length of 0.725mm. Figure 3(A) shows images that we obtained using the metalens. The smallest features on the resolution chart (lines with widths and center-to-center distances of 2.2 and 4.4μm, respectively) are well resolved. We repeated this experiment at different wavelengths. Figure 3(B–E) shows that the metalens can resolve these micron-sized lines across the visible range. We also fabricated arrays of nanoscale holes—see Figure 3(F)—by focused ion beam to further test the resolving power of our design. The metalens formed a clear image of the H-shaped object with all holes resolved, as shown in Figure 3(G). Moreover, the quality of this image is comparable to that formed by a commercial objective lens: see Figure 3(H). We tested the resolution limit of the metalens by imaging four holes with a subwavelength gap of ∼450nm: see Figure 3(I). Figure 3. Images obtained with a metalens Images obtained with a metalens 9 of diameter 2mm and focal length 0.725mm. The metalens is designed to operate at a wavelength of 532nm. (A) Image of the 1951 United States Air Force (USAF) resolution chart (Thorlabs Inc.) formed by the metalens at a wavelength of 530nm. Scale bar: 40μm. Images of the smallest feature size—the highlighted region in Figure 3(A)—on the USAF resolution chart at wavelengths of (B) 480, (C) 530, (D) 590, and (E) 620nm. Scale bars: 5μm. The differences in the image size occur as a result of the wavelength-dependent focal length. For example, a magnification of 167× is obtained at a wavelength of 620nm, compared to a magnification of 138×at 532nm. (F) SEM image of the nanoscale H-shaped target (fabricated by a focused ion beam). The minimum gap between two neighboring holes is ∼800nm. Image of the H-shaped target formed by (G) the metalens and (H) a commercial objective with the same NA (0.8). Scale bars: 10μm. (I) Image showing the ability of the metalens to resolve nanoscale holes with subwavelength gaps of 450nm. Scale bars: 500nm. Additionally, we have realized a chiral metalens (CML)—which forms two images with opposite helicities—by exploiting the circular-polarization sensitivity of the nanofins.10 The CML is composed of interlaced arrays of two nanofin arrangements, shown in Figure 4(A–C). To determine its performance, we used the CML in a series of imaging experiments. First, we imaged a facet of a single-mode fiber. To control the polarization state of the incident beam, we placed a linear polarizer and a quarter-waveplate between the fiber and the CML. The fiber was pumped by a tunable laser with a center wavelength and bandwidth of 550 and 100nm, respectively. The images, captured by a color camera—see Figure 4(D–F)—show that the metalens can simultaneously focus and disperse the broadband incident light. The rainbow-like images are obtained as a result of the dispersion-engineering design of the CML (accomplished by suitably selecting the off-axis focusing angle of the CML). As is expected for linearly polarized light (i.e., the result of superposition between left-circularly polarized and right-circularly polarized components with equal intensities), two identical images are formed within the camera's field of view. Figure 4. Multispectral chiral imaging. Multispectral chiral imaging. 10 (A) The building block of the chiral metalens (CML), consisting of two nanofins on a glass substrate. SEM images showing (B) the top view and (C) the side view of the fabricated CML. Of the two false-colored interlaced arrays of nanofins, the blue nanofins impart the phase required to focus incident right-circularly polarized light, while the green nanofins focus left-circularly polarized light. Scale bars: 600nm. (D) The CML forms two images of a single-mode fiber facet in the field of view of a color camera. Light is linearly polarized. (E) Image formed by the CML when the polarization state is left-circularly polarized. (F) Image formed under right-circularly polarized illumination. Scale bars are 500μm. (G) Two side-by-side images of a beetle, formed within the same field of view by the metalens. Illumination was provided by a green LED paired with a band-pass filter with a 10nm bandwidth centered at 532nm. We examined the chiral response of the CML by changing the polarization of the incident light to left-circular. For this polarization, fading of the right-side image—see Figure 4(E)—is accompanied by an increase to the intensity of the left-side image. By switching the chirality of the incident light, the opposite effect is observed, as shown in Figure 4(F). We also used our CML to image a biologically chiral specimen (Chrysina gloriosa, a beetle with inherent circular dichroism, CD). As shown in Figure 4(G), the CML simultaneously forms two images of the beetle on the camera chip. These two images possess opposite chirality, and their contrast showcases the very strong CD of the beetle's exoskeleton. In summary, we have developed a metasurface platform for visible wavelengths based on ALD-prepared TiO . In doing so, we have fabricated high-performance metalenses with a high efficiency and NA that allow for g focusing and high-resolution imaging. Futhermore, we have demonstrated the flexibility of this platform by realizing a multifunctional metalens with a planar and compact configuration. Together with its simple fabrication (by one-step lithography), this high-performance and versatile platform could find many applications in optics, ranging from imaging and spectroscopy to laser-fabrication processes. In our next step, we plan to realize an achromatic metalens that is suitable for white-light imaging. This development will greatly extend the scope of applications from single-wavelength imaging and spectroscopy to general microscopy, as well as potential mainstream-camera imaging devices. Harvard University Federico Capasso is the Robert Wallace Professor of Applied Physics. He joined Harvard University in 2003 after 27 years at Bell Labs, where his career advanced from postdoctoral fellow to vice president for physical research. He and his group have made wide-ranging contributions to optics, photonics, and nanotechnology, including pioneering the bandgap-engineering technique, the invention of the quantum cascade laser, the first measurement of the repulsive Casimir force, and (more recently) research on metasurfaces and their applications (including flat lenses and the generalized Snell's law). He is a member of the National Academy of Sciences, the National Academy of Engineering, the American Academy of Arts and Sciences, and a foreign member of the Accademia dei Lincei. His awards include the SPIE Gold Medal, the IEEE Edison Medal, the American Physical Society Arthur L. Schawlow Prize, and the King Faisal Prize. 4. S. B. Glybovski, S. A. Tretyakov, P. A. Belov, Y. S. Kivshar, C. R. Simovski, Metasurfaces: from microwaves to visible, Phys. Rep. 634, p. 1-72, 2016. 7. A. Arbabi, Y. Horie, M. Baheri, A. Faraon, Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission, Nat. Nanotechnol. 10, p. 937-943, 2015. 8. R. C. Devlin, M. Khorasaninejad, W. T. Chen, J. Oh, F. Capasso, High efficiency dielectric metasurfaces at visible wavelengths, arXiv 1603.02735 [physics.optics], 2016. 9. M. Khorasaninejad, W. T. Chen, R. C. Devlin, J. Oh, A. Y. Zhu, F. Capasso, Metalenses at visible wavelengths: diffraction-limited focusing and subwavelength resolution imaging, Science 352(6290), p. 1190-1194, 2016. 10. M. Khorasaninejad, W. T. Chen, A. Y. Zhu, J. Oh, R. C. Devlin, D. Rousso, F. Capasso, Multispectral chiral imaging with a metalens, Nano Lett. 16, p. 4595-4600, 2016. 11. R. C. Devlin, A. Ambrosio, D. Wintz, S. L. Oscurato, A. Y. Zhu, M. Khorasaninejad, J. Oh, P. Maddalena, F. Capasso, Spin-to-orbital angular momentum conversion in dielectric metasurfaces, arXiv 1605.03899 [physics.optics], 2016. 12. S. Pancharatnam, Generalized theory of interference and its applications, Proc. Ind. Acad. Sci. 44, p. 398-417, . 13. M. V. Berry, The adiabatic phase and Pancharatnam's phase for polarized light, J. Mod. Opt. 34, p. 1401-1407, 1987.
AUVSI Unmanned Systems 2014 | Year: 2014
In 2009, the US Air Force implemented an Undergraduate Remotely Piloted Aircraft Pilot Training (URT) program, which certifies and dedicates pilots solely to UAS operations. (Note: the USAF uses RPA in place of Group IV/V Unmanned Aircraft). Previously, the USAF used Joint Specialized Undergraduate Pilot Training (JSUPT) pilots, trained to fly manned aircraft. The USAF's Launch and Recovery (LR) training squadron, which teaches the MQ-9/MQ-1 RPA take-off & landing course to RPA pilots, conducted a study comparing pilot performance in the LR course between graduates of URT against graduates of JSUPT. This paper provides background on the USAF RPA pilot certification and training pipeline for Group IV/V UAS, contrasts the performance of three, differently trained and experienced, groups of RPA pilots in the Launch and Recovery course, and discusses observations from RPA Launch and Recovery instructors. This study showed that the less experienced URT pilots had more trouble initially in the areas of instrument cross check, airmanship and mission management but finished the LR program with similar check ride pass rates to more experienced, previous manned aircraft pilots. A secondary objective of this paper is to provide useful information on Group IV/V UAS training as the FAA establishes UAS operator training and certification requirements and industry launches UAS flight training programs.
Thomas N.,USAF |
Brook I.,Georgetown University
Expert Review of Anti-Infective Therapy | Year: 2011
Human and animal bites may lead to serious infection. The organisms involved tend to originate from the oral cavity of the offending biter, as well as the environment where the injury occurred. A variety of aerobic as well as anaerobic organisms have been isolated from bite wounds, with infection ranging from localized cellulitis to systemic dissemination, leading to severe disease ranging from abscess to bone and joint infection, to endocarditis and brain abscess. Immediate wound management, including recognition of the most commonly associated infectious pathogens, and judicious use of empiric antibiotics are crucial in providing the best care after a bite. Here, we discuss the common animal bite associated infections, and provide the most up to date information regarding their management. © 2011 Expert Reviews Ltd.