Aural stealth for night vision portable imagers

Modern tactics for carrying out military and antiterrorist operations calls for the development of a new generation of enhanced portable infrared imagers. The high performance of these imagers relies on the focal plane arrays, which are maintained at cryogenic temperatures using rotary Stirling cryogenic engines. These engines are known as powerful sources of wideband vibration export. For the sake of weight and compactness, the enclosure of the above imager is usually designed in the form of a light metal thin-walled shell, accommodating a directly mounted Infrared Detector Dewar Cooler Assembly. The operation of the device typically leads to an excitation of the inherently lightly damped structural resonances and therefore, to a radiation of the specific acoustic signature capable of compromising the aural stealth of the IR imager. Such a noisy IR imager may be detected from quite a long distance using enhanced sniper detection equipment or even aurally spotted when used in a close proximity to the target. Numerous efforts were taken towards achieving the desired inaudibility level, apparently becoming one of a crucial figure of merit characterizing the portable IR imager. However, even the best examples of modern should-be silent imagers are quite audible from as far as 50 meters. The presented research intends to improve the aural stealth of the portable IR imager by using three different approaches: First, by compliantly mounting the Infrared Detector Dewar Cooler Assembly where the stiffness and damping of the vibration protective pad are optimized for the best acoustical performance without developing excessive line of sight jitter. Secondly, by using the concept of the weak radiator to reshape the enclosure mode shapes, and finally developing a multi-modal distributed dynamic absorber (MMDA) to enhance the absorption of the vibrating structure. The multi-modal characteristic of such a dynamic absorber makes it highly dynamically reactive through a wide frequency range (20 kHz) of excitation. It will be shown that incorporating a MMDA into the vibrating structure will result in ultra range vibration attenuation, making the IR aurally silent

Final Design and On-Sky Testing of the iLocater SX Acquisition Camera: Broadband Single-Mode Fiber Coupling

Enabling efficient injection of light into single-mode fibers (SMFs) is a key requirement in realizing diffraction-limited astronomical spectroscopy on ground-based telescopes. SMF-fed spectrographs, facilitated by the use of adaptive optics (AO), offer distinct advantages over comparable seeing-limited designs, including higher spectral resolution within a compact and stable instrument volume, and a telescope independent spectrograph design. iLocater is an extremely precise radial velocity (EPRV) spectrograph being built for the Large Binocular Telescope (LBT). We have designed and built the front-end fiber injection system, or acquisition camera, for the SX (left) primary mirror of the LBT. The instrument was installed in 2019 and underwent on-sky commissioning and performance assessment. In this paper, we present the instrument requirements, acquisition camera design, as well as results from first-light measurements. Broadband single-mode fiber coupling in excess of 35% (absolute) in the near-infrared (0.97-1.31{\mu}m) was achieved across a range of target magnitudes, spectral types, and observing conditions. Successful demonstration of on-sky performance represents both a major milestone in the development of iLocater and in making efficient ground-based SMF-fed astronomical instruments a reality.Comment: 18 pages, 17 figures. Accepted for publication in MNRA

Development of an optical sensor for real-time weed detection using laser based spectroscopy

The management of weeds in agriculture is a time consuming and expensive activity, including in Australia where the predominant strategy is blanket spraying of herbicides. This approach wastes herbicide by applying it in areas where there are no weeds. Discrimination of different plant species can be performed based on the spectral reflectance of the leaves. This thesis describes the development of a sensor for automatic spot spraying of weeds within crop rows. The sensor records the relative intensity of reflected light in three narrow wavebands using lasers as an illumination source. A prototype weed sensor which had been previously developed was evaluated and redesigned to improve its plant discrimination performance. A line scan image sensor replacement was chosen which reduced the noise in the recorded spectral reflectance properties. The switching speed of the laser sources was increased by replacing the laser drivers. The optical properties of the light source were improved to provide a more uniform illumination across the viewing area of the sensor. A new opto-mechanical system was designed and constructed with the required robustness to operate the weed sensor in outdoor conditions. Independent operation of the sensor was made possible by the development of hardware and software for an embedded controller which operated the opto-electronic components and performed plant discrimination. The first revised prototype was capable of detecting plants at a speed of 10 km/h in outdoor conditions with the sensor attached to a quad bike. However, it was not capable of discriminating different plants. The final prototype included a line scan sensor with increased dynamic range and pixel resolution as well as improved stability of the output laser power. These changes improved the measurement of spectral reflectance properties of plants and provided reliable discrimination of three different broadleaved plants using only three narrow wavelength bands. A field trial with the final prototype demonstrated successful discrimination of these three different plants at 5 km/h when a shroud was used to block ambient light. A survey of spectral reflectance of four crops (sugarcane, cotton, wheat and sorghum) and the weeds growing amongst these crops was conducted to determine the potential for use of the prototype weed sensor to control spot-spraying of herbicides. Visible reflectance spectra were recorded from individual leaves using a fibre spectrometer throughout the growing season for each crop. A discriminant analysis was conducted based on six narrow wavebands extracted from leaf level spectral reflectance measured with a spectrometer. The analysis showed the potential to discriminate cotton and sugarcane fro

Design and Development of an in-house Scanning Tunneling Microscope System

ABSTRACT The invention of Scanning Tunneling Microscope (STM) by Binnig and Rohrer in 1982 eliminated the use of optical lenses and replaced the conventional optical microscopes with a new class of microscopes called the Scanning Probe Microscopes (SPM). Because of their unique characteristics such as higher resolution and acquisition of nano level images without affecting the physical properties of the sample, they have found wide applications in a variety of scientific disciplines such as biology, material science and electrochemistry. After considerable advancements in instrumentation, the STM has evolved as a nanomanipulation and nanofabrication tool. It operates in two modes: constant current mode and constant height mode. In constant current mode, the feedback parameter is the tunneling current based on which the voltage applied to the piezoelectric actuator is varied. Hence, the tip height is varied in accordance with this tunneling current. In the constant height mode, however, the height is maintained at a constant value and hence the voltage applied to the piezoelectric actuator is adjusted (PZT). Unlike constant current mode, it is the tunneling current which changes according to the surface profile and the local electronic structure of the tip and the sample. The present research is an effort in designing and fabricating an in-house STM to be operated in the constant current mode by interfacing various subsystems. The various subsystems constituting the experimental setup mainly include a micro positioner, a nano stager, STM Electronics, and STM head. The fabrication process involved testing and verification of a suitable preamplifier for providing the feedback signal, design of the STM head and development of a computer automated system in order to facilitate the acquisition of signals related to a micro positioner which acts as the coarse positioner. The software control consists of ControlDesk¨ as the front end and Simulink¨ as the backend. An optical subsystem in the form of a high resolution camera that has been interfaced facilitates visual monitoring and development of dual stage control of the fine as well as coarse positioners. The ability of the STM to acquire images at the nano level is attributed to the tip to sample interaction based on quantum mechanical tunneling. To better understand the aspects of STM, the present work also traces the development of theoretical modeling of the tip-sample interaction and the conceptual design of other classes of microscopes belonging to the SPM family. Certain hardware limitations associated with the data acquisition board need to be addressed in order to acquire nanolevel images. The future scope of the research would include development and testing of various types of controllers on the STM test bed

Integrating cavity based gas cells: a multibeam compensation scheme for pathlength variation

We present a four beam ratiometric setup for an integrating sphere based gas cell, which can correct for changes in pathlength due to sphere wall contamination. This allows for the gas absorption coefficient to be determined continuously without needing to recalibrate the setup. We demonstrate the technique experimentally, measuring methane gas at 1651nm. For example, contamination covering 1.2% of the sphere wall resulted in an uncompensated error in gas absorption coefficient of ≈41%. With the ratiometric scheme, this error was reduced to ≈2%. Potential limitations of the technique, due to subsequent deviations from mathematical assumptions are discussed, including severe sphere window contamination

Telescope to Observe Planetary Systems (TOPS): a high throughput 1.2-m visible telescope with a small inner working angle

The Telescope to Observe Planetary Systems (TOPS) is a proposed space mission to image in the visible (0.4-0.9 micron) planetary systems of nearby stars simultaneously in 16 spectral bands (resolution R~20). For the ~10 most favorable stars, it will have the sensitivity to discover 2 R_E rocky planets within habitable zones and characterize their surfaces or atmospheres through spectrophotometry. Many more massive planets and debris discs will be imaged and characterized for the first time. With a 1.2m visible telescope, the proposed mission achieves its power by exploiting the most efficient and robust coronagraphic and wavefront control techniques. The Phase-Induced Amplitude Apodization (PIAA) coronagraph used by TOPS allows planet detection at 2 lambda/d with nearly 100% throughput and preserves the telescope angular resolution. An efficient focal plane wavefront sensing scheme accurately measures wavefront aberrations which are fed back to the telescope active primary mirror. Fine wavefront control is also performed independently in each of 4 spectral channels, resulting in a system that is robust to wavefront chromaticity.Comment: 12 pages, SPIE conference proceeding, May 2006, Orlando, Florid

Optical deep space communication via relay satellite

The possible use of an optical for high rate data transmission from a deep space vehicle to an Earth-orbiting relay satellite while RF links are envisioned for the relay to Earth link was studied. A preliminary link analysis is presented for initial sizing of optical components and power levels, in terms of achievable data rates and feasible range distances. Modulation formats are restricted to pulsed laser operation, involving bot coded and uncoded schemes. The advantage of an optical link over present RF deep space link capabilities is shown. The problems of acquisition, pointing and tracking with narrow optical beams are presented and discussed. Mathematical models of beam trackers are derived, aiding in the design of such systems for minimizing beam pointing errors. The expected orbital geometry between spacecraft and relay satellite, and its impact on beam pointing dynamics are discussed

NASA Tech Briefs Index, 1977, volume 2, numbers 1-4

Announcements of new technology derived from the research and development activities of NASA are presented. Abstracts, and indexes for subject, personal author, originating center, and Tech Brief number are presented for 1977

Experiment definition phase shuttle laboratory, LDRL-10.6 experiment. Shuttle sortie to ground receiver terminal

System development and technology are described for a carbon dioxide laser data transmitter capable of transmitting 400 Mbps over a shuttle to ground station link