This PDF file contains the editorial “Editorial: Year 1993 in Review” for OE Vol. 33 Issue 02

This PDF file contains the editorial “Guest Editorial: Magnetospheric Imagery and Atmospheric Remote Sensing-Part 2” for OE Vol. 33 Issue 02

The proposed Inner Magnetosphere Imager mission will obtain the first simultaneous images of the component regions of the inner magnetosphere and will enable scientists to relate these global images to internal and external influences, as well as local observations. We are performing at the George C. Marshall Space Flight Center a concept definition study of the proposed mission. The baseline mission calls for an instrument complement of approximately seven imagers to fly in an elliptical Earth orbit with an apogee of seven Earth radii (Re) and a perigee of approximately 4800 km. Several spacecraft concepts are being considered for the mission. The first concept utilizes a spinning spacecraft with a despun platform. The second concept splits the instruments onto two smaller satellites-a spinning spacecraft and a complementary three-axis stabilized spacecraft. Launch options being assessed for the spacecraft range from a Delta II, for the single- and dual-spacecraft concepts, to dual Taurus launches, for the two smaller spacecraft. An additional option, that of downsizing the mission to fit within the guidelines of the Space Physics Division's new class of solar terrestrial probes, is also being considered.

Imaging of the space plasma environment via low-energy neutral atoms (LENAs) promises to revolutionize the way in which largescale space plasma phenomena are viewed and understood. LENAs are produced by charge exchange between plasma ions (less than tens of kilo-electron-volts) and cold geocoronat neutrals; these LENAs radiate outward in all directions from their points of origin. Previously developed methods for imaging higher energy neutrals are not suitable for observing the majority of the terrestrial magnetosphere, which is comprised primarily of lower energy plasma populations. This paper briefly describes both the direct and indirect techniques that have been suggested for imaging LENAs to date. We then examine in more detail the most advanced of these techniques appropriate for magnetospheric imaging, indirect detection based on ionization of LENAs as they transit ultrathin foils. Such a LENA imager consists of four basic components: (1) a biased collimator to remove the ambient charged particles and set the azimuthal field of view; (2) an ultrathin foil, which ionizes a portion of the incident LENAs; (3) an electrostatic analyzer to reject UV light and set the energy passband; and (4) a coincidence position detector to measure converted LENAs while rejecting noise and penetrating radiation.

Imaging of the terrestrial magnetosphere is possible through the detection of low-energy neutral atoms (LENA5) produced by charge exchange between magnetospheric plasma ions and neutral atoms of the Earth's geocorona. We present calculations of both hydrogen and oxygen line-of-sight LENA fluxes expected on orbit for various plasma regimes as predicted by the Rice University Magnetospheric Specification Model. To decrease the required computation time, we are in the process of adapting our code for massively parallel computers. The speed gains achieved from parallel algorithms are substantial, and we present results from computational runs on the Connection Machine CM-2 data parallel supercomputer. We also estimate expected image count rates and image quality based on realistic instrument geometric factors, energy passbands, neutral atom scattering in the instrument, and image accumulation intervals. The results indicate that LENA imaging instruments will need a geometric factor (G) on the order of 0.1 cm² sr eV/eV to be capable of imaging storm time ring currents, and a G of 1.0 cm² sr eV/eV in order to image the quiet time ring current fluxes, ion injections from the tail, and subsequent ion drifts toward the dayside magnetopause.

Low-energy neutral atom (LENA) imaging promises to be a revolutionary tool for global imaging of space plasmas. The technical challenges of LENA detection include separating them from the intense ambient UV without losing information about their incident trajectories, quantifying their trajectories, and obtaining high-sensitivity measurements. Two techniques that have been proposed for this purpose are based on fundamentally different atomic interaction mechanisms between LENAs and a solid: LENA transmission through an ultrathin foil and LENA reflection from a solid surface. Both of these methods provide LENA ionization (for subsequent removal from the UV by electrostatic deflection) and secondary electron emission (for time-of-flight start pulse generation and/or coincidence). We present a comparative study of the transmission and reflection techniques based on differences in atomic interactions with solids and surfaces. Transmission methods are shown to be superior for secondary electron emission rather than reflection methods. Furthermore, transmission methods are shown to be sufficient for LENA imaging at LENA energies of approximately 1 keV to greater than 30 keV. A hybrid instrument using reflection from a low work function surface for LENA ionization and transmission for secondary electron emission is optimal for imaging of LENAs with energies less than approximately 1 keV.

Recently proposed low-energy neutral atom (LENA) imaging techniques rely on collisional processes to convert LENAs into ions to separate the neutrals from the intense UV radiation background. At low energies, these collisional processes have poor conversion efficiencies and limit the angular resolution of these devices. However, if the intense UV light background can be suppressed, direct LENA detection is possible. We present results from a series of experiments designed to develop a novel filtering structure based on free-standing gold transmission gratings. If the grating period is sufficiently small, the gratings can substantially polarize UV light in the wavelength range 300 to 1500 Å. If a second grating is placed behind the first grating with its axis of polarization oriented perpendicular to that of the first, considerable attenuation of the UV radiation is achievable. The neutrals pass through the remaining open area of two gratings and are directly detected. We have obtained nominal 2000-Å-period (1000-Å bars with 1000-Å slits) gratings and measured their UV and atomic transmission characteristics. The geometric factor of a LENA imager based on this technology is comparable to that of other proposed LENA imagers, with a significantly better angular resolution.

We describe an instrument concept for measuring low-energy neutral H and O atoms with kinetic energies ranging from about 10 eV to several hundred. The instrument makes use of a low work function surface to convert neutral atoms to negative ions. These ions are then accelerated away from the surface and brought to an intermediate focus by a large aperture lens. After deflection in a spherical electrostatic analyzer, the ions are postaccelerated to ~25-keV final energy into a carbon-foil time-of-flight mass analyzer. Mass resolution is adequate to resolve H, D, He, and O. Energy and azimuth angle information is obtained by means of position imaging the secondary electrons produced at the carbon foil. A large geometric factor combined with simultaneous angle-energy-mass imaging that eliminates the need for duty cycles provide the necessary high sensitivity. From a spinning spacecraft this instrument is capable of producing a 2-D map of low-energy neutral atom fluxes.

EUV images from emissions of O⁺ (83.4 nm) and He⁺ (30.4 nm) distributions in the plasmasphere and trough regions are constructed for a satellite at 9 Re (where Re is Earth radii). A diffusive equilibrium model is used to describe the density distribution along the field lines for ions in the plasmasphere, and a kinetic collisionless model is assumedto calculate ion densities in the high-latitude regions beyond the plasmapause. In our model ofthe plasmasphere, we assumethat ions move along astatic dipole field. Observational data on O⁺ and He⁺ densities in the ionosphere are used as boundaryconditionsto calculatethespatial distribution of densities along the field lines. Assuming thatthe day and night boundary conditions are asymmetric and exobase densities vary with latitude, we discuss how this would be reflected in the intensities and structure of the magnetospheric images.

X-ray imagers can provide large-scale maps of bremsstrahlung x rays produced by electron precipitation into the atmosphere. Complete day and night coverage is obtained and the electron energy spectra at each position in space can be derived from the measured x-ray energy spectra. Early x-ray imagers were limited in field of view and to one map for each pass over the emitting regions. The Magnetospheric Atmospheric X-ray Imaging Experiment, launched on a TIROS satellite,makes time-space mappings by scanning a 16-pixel pinhole camera. The data distinguish intensity variations of a fixed auroral feature from motion of a steadily radiating feature. However, the spatial deconvolution is complex and features stay in the field of view for only ~10 mm. These problems will be resolved by a high-altitude (~9 Re) imaging spectrometer PIXIE on the ISTP/GGS Polar Satellite to be launched in 1994. PIXIE's position-sensitive proportional counter will continuously image the entire auroral zone for periods of hours.

We present a small Explorer mission, Imagers for the Magnetosphere, Aurora, and Plasmasphere (IMAP), to provide the first global magnetospheric images that will allow a systematic study of major regions of the magnetosphere, their dynamics, and their interactions. The mission objective is to obtain simultaneous images of the inner magnetosphere (ring current and trapped particles), the plasmasphere, the aurora, and auroral upflowing ions. The instrumentsare (1) a Low Energy Neutral Particle Imager for imaging H and O atoms, separately, in the energy range of ~1 to 30 keV, in several energy passbands; (2) an Energetic Neutral Particle Imager for imaging H atoms in the energy range ~15 to 200 keV and, separately, O atoms in the energy range ~60 to 200 keV, each in several energy passbands; (3) an Extreme-Ultraviolet Imager to obtain images of the plasmasphere (the distribution of cold He⁺) by means of He⁺ (30.4 nm) emissions; and (4) a Far-Ultraviolet Imaging Monochromator to provide images of the aurora and the geocorona. All images will be obtained with time and spatial resolutions appropriate to the global and macroscale structures to be observed. IMAP promises new quantitative analyses that will provide great advances in insight and knowledge of global and macroscale magnetospheric parameters. The results expected from IMAP will provide the first large-scale visualization of the ring current, the trapped ion populations, the plasmasphere, and the upflowing auroral ion population. Such images, coupled with simultaneously obtained auroral images, will also provide the initial opportunity to globally interconnect these major magnetospheric regions. The time sequencing of IMAP images willalso provide the initial large-scale visualization of magnetospheric dynamics, both in space and time.

Imaging upflowing O⁺ ions of ionospheric origin and plasmaspheric O⁺ can be achieved through solar resonance scattering at 834 Å. Unfortunately, several strong background emissions, including the ones at 1025 and 1216 Å due to geocoronal hydrogen atoms, pose serious problems. Most common optical coatings have higher reflectivity at 1025 and 1216 Å than at 834 Å. After examining a number of options, e have designed a multiple-layer coating that selectively reflects 834-Å radiation and suppresses 1025- and 1216-Å radiation. The structure of the coating material consists of a very thin (50 to 150 Å) metal (nickel) layer on top of a semitransparent dielectric material (magnesium fluoride) over an aluminum substrate. Three such coatings were produced at NASA Goddard Space Flight Center using an existing coating facility that is not optimized for thin coatings. In spite of such fabrication difficulties, we have obtained encouraging results.

Observations of bremsstrahlung x rays emitted by energetic electrons impacting the Earth's atmosphere can be used for remotely sensing the morphology, intensity, and energy spectra of electron precipitation from the magnetosphere. The utility of the technique is derived from the broad energy range of observable x rays (2 to >100 keV), the simple emission process, the large x-ray mean free path in the atmosphere, and negligible background. Two auroral x-ray imagers, developed for future spaceflights, are discussed. The Polar Ionospheric X-Ray Imaging Experiment is scheduled for launch on the NASA International Solar-Terrestrial Physics/Global Geospace Science program POLAR satellite in 1994. The POLAR orbit, with an apogee and perigee of 9 and 1.8 Re (Earth radii), respectively, affords the opportunity to image the aurora from a high altitude above the north pole continuously for several hours. The Magnetospheric Atmospheric X-Ray Imaging Experiment (MAXIE) was launched aboard the NOAA-I satellite on August 8, 1993. The 800-km polar orbit passes over both the northern and southern auroral zones every 101 mm. MAXIE will be capable of obtaining multiple images of the same auroral region during a single satellite orbit. The experimental approaches used to exploit these very different orbits for remote sensing of the Earth's auroral zones are emphasized.

The Naval Research Laboratory is developing a series of far- and extreme-ultraviolet spectrographs (800 to 1700 Å) to measure altitude profiles of the ionospheric and thermospheric airglow from the U.S. Air Force Defense Meteorological Satellite Program's Block 5D3 satellites. These spectrographs, which comprise the Special Sensor Ultraviolet Limb Imager (SSULI), use a near-Wadsworth optical configuration with a mechanical grid collimator, concave grating, and linear array detector. To image the limb, SSULI employs a rotating planar SiC mirror that sweeps the field of view perpendicular to the limb of the Earth. In the primary operating mode, the mirror sweeps the instrument field of view through 17 deg to view tangent heights from about 50 to 750 km. The SSULI detectors use microchannel plate intensification and wedge-and-strip decoding anodes to resolve 256 pixels in wavelength dispersion. The detector is windowless and uses an o-ring sealed door to protect the Csl photocathode from exposure prior to insertion in orbit. The altitude distributions of the airglow measured by the SSULI sensors will be used to infer the altitude distributions of electrons and neutral species. At night, electron densities will be determined by measurement of ion recombination nightglow. Daytime electron densities will be obtained from measurements of multiple resonant scattering of O⁺ 834-Å radiation produced primarily by photoionization excitation of atomic oxygen. Dayside neutral densities and temperatures will be inferred from the measurement of dayglow emissions from N₂ and O produced by photoelectron impact excitation.

The Remote Atmospheric and Ionospheric Detection System (RAIDS) experiment is an optical remote sensing platform consisting of eight sensors, (spectrographs, spectrometers, and photometers) covering the wavelength range 550 to 8744 Å. RAIDS employs a mechanical scan platform to view the Earth's limb and measure line-of-sight column emission from tangent altitudes from 50 to 750 km. These measurements provide vertical profiles of atmospheric dayglow and nightglow from the mesosphere to the upper regions of the F-region ionosphere. RAIDS will be flown on the National Oceanographic and Atmospheric Administration (NOAA) J weather satellite through the auspices of the U.S. Air Force Space Test Program. The RAIDS wavelength and altitude coverage allows remote sensing of the major and many minor constituents in the thermosphere and ionosphere. These measurements will be used as part of a proof of concept for remote sensing of ionospheric and neutral density profiles. The RAIDS database will be used to study composition, thermal structure, and couplings between the mesosphere, thermosphere, and ionosphere. RAIDS is a joint venture of the Naval Research Laboratory (NRL) and The Aerospace Corporation. We describe the subset of RAIDS instruments developed at NRL covering the far to near UV regions (1300 to 4000 Å).

A NASA sounding rocket experiment was developed to study the solar extreme-ultraviolet (EUV) spectral irradiance and its effect on the upper atmosphere. Both the solar flux and the terrestrial molecular nitrogen via the Lyman-Birge-Hopfield bands in the far-ultraviolet (FUV) region were measured remotely from a sounding rocket on October 27, 1992. The rocket experiment also includes EUV instruments from Boston University, but only the National Center for Atmospheric Research's (NCAR)/University of Colorado's (CU) four solar instruments and one airglow instrument are discussed. The primary solar EUV instrument is a 0.25-m Rowland circle EUV spectrograph that has flown on three rockets since 1988 measuring the solar spectral irradiance from 30 to 110 nm with 0.2-nm resolution. Another solar irradiance instrument is an array of six silicon soft x-ray (XUV) photodiodes, each having different metallic filters coated directly on the photodiodes. This photodiode system provides a spectral coverage from 0.1 to 80 nm with ~15-nm resolution. The other solar irradiance instrument is a silicon avalanche photodiode coupled with pulse height analyzer electronics. This avalanche photodiode package measures the XUV photon energy, providing a solar spectrum from 50 to 12,400 eV (25 to 0.1 nm) with an energy resolution of about 50 eV. The fourth solar instrument is an XUV imager that images the sun at 17.5 nm with a spatial resolution of 20 arc sec. The airglow spectrograph measures the terrestrial FUV airglow emissions along the horizon from 125 to 160 nm with 0.2-nm spectral resolution. The photon-counting CODACON detectors are used for three of these instruments and consist of coded arrays of anodes behind microchannel plates.

We have developed a prototype spectrometer for space applications that require long-term stable EUV photon flux measurements. In this recently developed spectrometer, the energy spectrum of the incoming photons is transformed directly into an electron energy spectrum by taking advantage of the photoelectric effect in one of several rare gases at low pressures. Using an electron energy spectrometer operating at a few electron volts, and followed by an electron multiplying detector, pulses due to individual electrons are counted. The overall efficiency of this process is essentially independent of gain drifts in the signal path, and the secular degradation of optical components that is often a problem in other techniques is avoided.

To take advantage of the large luminosity-resolution product of the Fabry-Pérot interferometer used in tandem with modest-aperture telescopes, a Fabry-Pérot interferometer has been developed that is widely adaptable to a variety of extended source observations. The instrument is designed for adaptability across a range of optical and near-IR (NIR) spectral lines from 550 to 1100 nm, which are characterized by a wide range of velocity distributions of the emitting species. The system features a twin-étalon configuration to provide an extended free spectral range and to enhance contrast when observations include bright reflected solar or twilight backgrounds. Although the optical path and all the optical elements of the system are readily accessible, the instrument is ruggedized for transportability and extended remote field operation once it is optically configured. State-of-the-art, modularly adaptable, proven detectors (GaAs photomultipliers, large CCDs, and germanium integrating detectors) are featured to optimize instrument sensitivity. Recently, a series of NIR observations were made at the Millstone Hill Incoherent Scatter Radar Facility, Westford, Massachusetts, in a single-étalon mode.

The application of Fabry-Pérot interferometers (FPls) to the study of upper atmosphere thermodynamics has largely been restricted by the very low light levels in the terrestrial airglow as well as the limited range in wavelength of photomultiplier tube (PMT) technology. During the past decade, the development of the scientific grade charge-coupled device (CCD) has progressed to the stage in which this detector has become the logical replacement for the PMT. Small fast microcomputers have made it possible to "upgrade" our remote field sites with bare CCDs and not only retain the previous capabilities of the existing FPIs but expand the data coverage in both temporal and wavelength domains. The problems encountered and the solutions applied to the deployment of a bare CCD, with data acquisition and image reduction techniques, are discussed. Sample geophysical data determined from the FPI fringe profiles are shown for our stations at Peach Mountain, Michigan, and Watson Lake, Yukon Territory.

A Hartman-sensor-based, adaptive optics system is analyzed using numerical simulation. The same simulation was used to quantify the lucky shot concept. One-dimensional, isoplanatic wavefronts were generated, containing the known spatial and statistical properties of atmospheric-turbulence-degraded wavefronts. The quality of the corrected wavefronts was analyzed as a function of different combinations of sensor (lenslet) number and correcting mirror number. It is shown that it is possible to reduce the number of correcting mirrors with no great loss of image quality. As a consequence of the wavefront simulation, it is shown that the lucky shot occurrence probability is very low.

Changes in the biomechanics and in the molecular texture and structure of isolated radioulnar bones of subadult European moose (Alces alces L.) collected in various environmentally polluted areas of Finland were investigated by means of holographic interferometric nondestructive testing (HNDT), radiological, morphometrical, and x-ray diffraction methods. By means of small caudal-cranial bending forces, the surface movements of the lower end (distal epiphysis) of the radial bone were recorded with the HNDT method. To study bone molecular texture and structure changes under external compressing forces, the samples for x-ray diffraction analysis were taken from the upper end of the ulnar bone (olecranon tip). Results showed that the bones obtained from the Harjavalta area and those of North Karelian moose showing malnutrition and healing femoral fractures produced different HNDT pictures compared with the four normally developed North Karelian moose. In the x-ray diffraction, the Harjavalta samples showed changes in molecular texture and structure compared with the samples from the apparently normal North Karelian animals.

The near-UV (190 to 270 nm) coronal emission lines present a unique opportunity to observe heliospheric plasmas between one and two solar radii. The near-UV coronagraph was specifically designed to obtain observations in these lines from a sounding rocket platform. The design demonstrates that high-resolution, two-dimensional coronal observations in the near-UV are readily achievable within the practical constraints of a sounding rocket. The near-UV coronagraph consists of a reflective, coronagraph telescope followed by an imaging channeled spectrograph. The telescope includes a Lyot stop and an occulter to minimize instrumentally scattered disk radiation. The choice of a mirror objective gives rise to a compact, achromatic telescope with excellent off-axis rejection and good imaging properties. The focal plane package combines a Fabry-Pérot interferometer with a tandem Wadsworth spectrograph to produce a channeled spectrum consisting of a series of two-dimensional (25 x 500 arcsec), narrow-bandpass (~0.1 Å) images at the instrument focal plane. The instrument will produce a number of high-spatial-resolution (< 1 arcsec) coronal images in a single flight.

A method is described for obtaining moderate frequency stability of a multimode pulsed dye laser and several factors are discussed that affect the stability. We describe the experimental setup, give the experimental results, and demonstrate that even when the linewidth is 2 GHz, a frequency stability of better than ±20 MHz is possible.

Twelve existing lifetime models for optical fibers, based on a power law to describe the stress-enhanced crack growth, are studied and compared. The number of models is reduced to only one basic model. This model takes into account the effects of a proof test. An alternative model, to be used when proof testing is performed on line, is given as a worst case limit. A choice of three testing methods to obtain information about the weak-flaw distribution is given: dynamic fatigue and variable screen testing of long lengths or the use of a failure number during the proof test. We show that the part of the crack growth that is controlled by transport of the reaction agent instead of by reaction speed (described by the power law) does not influence the model. It is also shown that weakening of the fiber during unloading has a minor effect on the presented model. The lifetime model cannot be used for fibers in water without further study.

A numerical model was developed to calculate the modal phase shift of a circular step index profile weakly guiding optical fiber under axial strain. Whenever an optical fiber is under stress, the optical path length, the index of refraction, and the propagation constants of each mode change. In consequence, the phase of each mode is alsomodified. A relationship for the modal phase shift is presented. This relation is applied to bpth single-mode and two-mode fibers to determine the sensitivity characteristics of strained fibers. It was found that the phase shift is strongly dependent on the core refractive index n_co. It was also found that it is possible to design fibers that are insensitive to axial strain. Practical applications of strain-insensitive fibers are discussed.

A fiber optic radiometer based on a cooled photonic detector was designed and constructed. The radiometer is capable of measuring in real time the temperature of tissue irradiated with a CO₂ laser. A silver halide IR fiber is used to deliver the CO₂ laser radiation to the target and also to deliver the thermal radiation emitted from the target back to the detector. Two methods of measurements were examined, both of which solve the problem of detector blinding by reflected CO₂ radiation. A theory of operation for this silver halide fiber optic radiometer, based on lock-in amplifier techniques, is presented. A short discussion of the radiometer design and construction is given. This work forms a basis for the subject of measuring, in real time, fast radiometric signals caused by CO₂ laser irradiation. Such a radiometer is very useful when dealing with pulsed photo thermal radiation with 10.6-μm CO₂ laser radiation. This technique is very useful in medicine and industry.

A critical review and comparison of the initiation of combustion processes by conventional electric spark or thermal means with laser sources is presented. A description of the fundamentals of ignition processes is used as the basis for interpretation of experimental and theoretical studies of laser ignition. It is shown that many features of laser ignition can be understood on the basis of simple thermal concepts, particularly when the effects of thermal or radical losses are considered. It is proposed that the main advantages of laser sources are likely to be in the timing and placement of ignition rather than the inherent energy requirements. Potential applications to combustion systems of practical importance, e.g., high-speed propulsion systems, are discussed and instructive laboratory-scale experiments are suggested.

A frequency-selective technique is proposed to improve the performance of joint-transform correlators. In this technique, the useless part of the Fourier transform interference intensity for creating the correlation signal of the joint-transform correlator is removed. Two architectures to achieve this goal are also presented. It is shown that dramatic improvement (as large as 200%) in the autocorrelation peak amplitude of the joint-transform correlator is possible by means of the proposed technique. Similar to the bipolar joint-transform correlator, the bipolar frequency-selective joint-transform correlator has a delta-function-like autocorrelation signal. In addition, it provides similar discrimination ability and noise performance to the bipolar joint-transform correlator.

We explore the features of a family of nonlinear filters called the fractional order mean. The median, the mode, and other statistical characteristics belong to this family as particular integer orders. The behavior of these filters in noise suppression in images is investigated. An improved version of these filters, which we call the 8-pixel window mean filter is also explored. In this case, the filtered value of the pixel is compared with its experimental value in the presence of a preset threshold. Noise suppression performance is tested with the usual mean square error (MSE) criterion, with a correlation criterion, and with a new criterion, the mean relative error (MRE). Evidence is found that the MRE correlates better than the MSE with the perceived visual quality of the processed image.

Realization of a two-dimensional discrete Walsh transform (DWT) by matrix-vector multiplication in an optical architecture is presented. Although data are entered sequentially, the parallelism of optical architecture is exploited in the proposed system and, therefore, the computation time required to obtain the DWT is less when compared to its equivalent electronic system. The hardware realization is achieved with the help of a microprocessor.

We present a residue-based method in which the operations of decimal numbers of any magnitude can be processed using only two relatively prime moduli, 2 and 5. We suggest a method of implementation of addition and subtraction using different optical systems. Although the method suffers primarily from the difficulties associated with decimal carrying, we deal with these by means of a separate carry generator that can also be operated in parallel, thus reducing the number of steps.

We present a pendulum iterative algorithm (PIA) to solve the phase retrieval problem. Computer simulations show that, in general, PIA converges faster than previous iterative algorithms in which the moduli of the object and the Fourier domain are provided. The performance of the PIA is compared with that of the error-reduction algorithm (ERA), the modified error-reduction algorithm (MERA), the input-output algorithm (IOA), and the hybrid IOA/ERA algorithm. We show that the PIA generally performs better for a binary modulus. In the case of a multilevel modulus, the PIA performs comparable to the hybrid IOA/ERA, while better than the others.

Cumulants are employed for classification and synthesis of textured images because they suppress additive Gaussian noise of unknown covariance and are capable of resolving phase and causality issues in stationary non-Gaussian random fields. Their performance is compared with existing autocorrelation-based approaches that offer sample estimates of smaller variance and lower computational complexity. Nonlinear matching techniques are better than linear equation methods in estimating parameters of non-Gaussian random fields especially under model mismatch. Seasonal 1-D sequences allow for semistationary 2-D models, and their performance is illustrated on synthetic spacevariant textures. The potential of prolate spheroidal basis expansion is also described briefly for parsimonious nonstationary modeling of spacevariant textured images.

A method of calculating numerically the optical transfer function appropriate to any type of image motion and vibration, including random ones, has been developed. We compare the numerical calculation method to the experimental measurement; the close agreement justifies implementation in image restoration for blurring from any type of image motion. In addition, statistics regarding the limitation of resolution as a function of relative exposure time for low-frequency vibrations involving random blur are described. An analytical approximation to the probability density function for random blur has been obtained. This can be used for the determination of target acquisition probability. A comparison of image quality is presented for three different types of motion: linear, acceleration, and high-frequency vibration for the same blur radius. The parameter considered is the power spectrum of the picture.

Standard digital video displays use 640 x 480 (NTSC) or 512 x 512 (PAL) pixels to display a full screen image, while observers searching such images for small targets (or reading text) will typically operate with a screen subtense of 25 x 35 deg. Often, however, the region of interest in these images may be about 100 x 100 pixels in size, and so subtend only about 5 x 5 deg on a standard screen. In this case enlargement-that is, increasing the angular subtense-of the region of interest may well be appropriate. To obtain a larger viewing angle, the image must be zoomed, with some form of interpolation being used to generate new intermediate pixels. This paper reports on two experiments in which the effects of various methods of zooming on target acquisition are psychophysically evaluated. The results show that zooming generally enhances performance, but that for zooming factors greater than 2, smooth zooming techniques need to be used.

A new progressive image transmission scheme in the spatial domain is developed. The proposed scheme is demonstrated to be applicable to many interactive image communications. The progressive transmission of images could solve the problems related to the lengthy time required to transmit high-resolution images over low-speed channels. The proposed scheme is required to be computationally simple but result in a bit rate improvement. This technique is also demonstrated to be capable of developing operators such as a selective fill-in function. This scheme has encoded an approximate binary image, initially using context-free encoding. The approximate binary image is represented by two lists of identical elements maintained by both sides of the communication, with each list recording the locations of regions of homogeneous intensity. The dynamic thresholding technique is then applied to progressively refine the image. The dynamic threshold is defined as the mean of intensities for each stage. The original list is partitioned by the thresholdings. The information required for updating the lists is compressed by both the prefix coding and the runlength coding. An image can be progressively refined in the future because both sides of the communication maintain the locational lists of the same content. Several computer simulations using the proposed scheme and the bit-plane method are used to illustrate the advantages of the proposed scheme, which is confirmed by performance comparisons to obtain a better result than the bit-plane method.

Photorefractive crystals such as iron-doped lithium niobate are versatile recording materials for holographic interferometry. These crystals are self-developing, erasable, and reusable, amply sensitive in the visible region, and possess large information storage capacity, making them attractive for routine interferometry applications. This paper summarizes a variety of experiments in interferometry using iron-doped and undoped lithium niobate crystals for recording the holograms. Double-exposure holography with an argon laser is applied to visualize aerodynamic flow fields, heat transfer patterns, and acoustic waves. A pulsed Nd:YAG laser is used to visualize the details of turbulent aerodynamic fields. Finally, several heat transfer patterns are visualized by holographic subtraction interferometry and real-time interferometry.

We propose a method to obtain the shape of a large plane surface by connecting phase distributions measured by a small-aperture interferometer. These separately measured phase distributions cannot be connected directly because the object will tilt or have vertical displacement during the measurements. To correct these errors, the measurements are made so that the adjacent interferograms have common areas, and these interferograms are connected to minimize the difference of the phase distributions in the common areas. A matrix equation is derived to obtain coefficients to correct tilt and vertical displacement, and the accuracy of connection increases in proportion to an exponent of 1.5 of the width of the common area.

Light-emitting diode emission behaviors at a very weak injection current level are studied using the photon-counting method. It is observed that the emission is superlinearly dependent on the injection current irrespective of the emitting wavelength. The bending point of the L:I plot is different from that of the V:I plot. The bimolecular emission nature is interpreted to be a nonradiative transition mechanism due to some deep level trapping.

Electro-optic products sometimes require sapphire plate lenses of high quality that are highly accurate in terms of flatness and parallelism and are in a scratch-free condition. This is difficult to achieve by conventional methods (for example, with a general polishing machine, single-sided polishing machine, etc.). In addition, the preparation of the laps and the lapping process are inconvenient and time consuming. We have designed a new method for lapping sapphire flat lenses that is based on the mechanism of the correction of a double-sided lapping machine's lapping plate and the measurement of highly accurate parallelism by means of lateral shearing interference. This method can accurately and efficiently lap extremely hard sapphire flat lenses.

Two-dimensional fiber optic arrays are fabricated for the input and output to a prototype 16-element optical crossbar switch. The switch input comprises a 4 x 4 square array of 125-μm-diam, polarization-preserving fibers with a 5-μm core. The interfiber spacing was 200 μm. For the output array, a larger 4 x 4 square array of 140-μm-diameter, 100-μm-core, multimode fibers was constructed. Interfiber spacing for this array was 800 μm. Correct positioning of the optical fibers was achieved using location holes. These were laser machined in polyimide for the input array and chemically etched in silicon for the output array. A supporting matrix of epoxy adhesive was used to allow polishing of the arrays. Location hole positions were generated to within ±3 μm in both substrate materials, although hole tapering is observed. The effects of hole tapering on fiber orientation have been minimized by aligning two separate hole arrays. Polarization errors for the input array are typically ±10 deg. Mean errors in fiber position for the partially polished input and output arrays were 3.6 and 6.3 μm, respectively. Positional errors can be reduced to the positioning accuracy of the location holes by further polishing of the fiber-matrix structure. Methods for further reducing positional errors in the future are discussed.

We applied near-field total internal reflection holography to solve the problems of miniaturization of lenslet arrays. A regular 100 x 100 lenslet array with a 390-μm focal length and a nonregular lenslet array for clock distribution to a specially designed VLSI circuit were recorded in a planar-optics configuration. We also developed an appropriate recording technique to satisfy both the low-aberration condition and the Bragg condition, despite a wavelength shift between the recording and readout.

The optical interference coatings that have been successfully used in the Chinese FY-1 Meteorological Satellite and airborne remote sensing instruments are described. The system requirements for these coatings, the design approach, fabrication techniques, and the results achieved are presented.

Two-dimensional arrays of Fresnel zone microlenses were fabricated and coated with antireflection layers by an ion beam sputter deposition technique. The reflection of these lenses was analyzed on the basis of an angular spectrum approach for different substrate materials. A minimum reflectivity as low as 2 x 10^-4 was realized by means of in situ controlled multilayers of TiO₂ and SiO₂. The lenses have a circular aperture of 2 mm and different focal lengths for the wavelengths of 1.52 and 0.63 μm, respectively. The kinoform profile in each zone of the Fresnel zone lenses was approximated by an eight-level profile. Such stepped profiles were realized with several masks written with an electron beam and transferred by photolithographic technology. Our measurements reveal that the spot sizes of the fabricated microlenses are close to the diffraction-limited values, and the highest measured diffraction efficiencies for the eight-level structures are greater than 80%.

This PDF file contains the editorial “Book Rvw: Electro-Optics Handbook," edited by Roland W. Waynant and Marwood N. Ediger for OE Vol. 33 Issue 02