Showing papers on "Image resolution published in 1971"

Millimeter wave holographic imaging of concealed weapons

Abstract: Experiments are described in which optical images of small metallic objects were reconstructed from millimeter wave phasigrams (phase-only holograms). Since the well-established term HOLOGRAM introduced first by Gabor implies a "total record," namely of amplitude and phase, the term phase-only hologram would be contradictory. The authors propose the term PHASIGRAM for a "phase record" based on the Greek work "phasis" for phase. Sufficient resolution is present in the images obtained to allow the identification of a toy metallic gun, even when covered with a layer of clothing or synthetic leather. The phase distribution of the 70-GHz millimeter wave field scattered by the object was determined by mechanically scanning a harmonic mixer over a 0.75-m diameter circular aperture in a spiral pattern. The resulting electrical phase signal was converted to a light intensity pattern which was recorded on photographic film. A He-Ne laser was used to illuminate a reduced transparency replica of the recorded phasigrams and reconstruct the images.

Clinical tests on a prototype semiconductor gamma-camera

Abstract: A prototype γ-camera has been constructed from a slice of lithium-drifted germanium 44 × 44 mm in area and 6·5 mm in sensitive thickness. Positional information is obtained using the orthogonal strip principle, the inherent spatial resolution being 3 mm. Data are presented on energy resolution, uniformity, linearity of image and spatial resolution. The application to imaging distributions of 99Tcm in rats and humans is demonstrated, and comparisons on picture quality and background made (using the identical sources) with a conventional Anger system.

Efficient and aberration-free wavefront reconstruction from holograms illuminated at wavelengths differing from the forming wavelength.

Abstract: Recording materials producing higher efficiency, low absorption holograms are usually photosensitive only to blue and uv light. If a hologram is formed at a blue wavelength in such a material and is illuminated at a red wavelength, generally the reconstructed wavefront is aberrated, and the resolution of the image is reduced. A method of hologram formation is described that can alleviate this problem. In this method, a hologram H(1) is formed first at the red wavelength lambda(1) in a photographic emulsion. This hologram is then illuminated at the blue wavelength lambda(2) The diffracted wave from H(1) is used as the subject wave for forming the desired high efficiency hologram H(2). If certain requirements are met, illumination of H(2) at lambda(1) can produce an aberration-free reconstruction of the original subject wave. Experimental results of forming H(2) of a point source on dichromated gelatin film are presented. The hologram was formed at lambda(2) = 4800 A but could reconstruct an aberration-free wavefront at lambda(1) = 6328 A. The hologram had about 80% diffraction efficiency and essentially no absorption loss.

Parametric up-conversion from the infra-red

Abstract: The subject of up-conversion in optically nonlinear crystals is reviewed. The characteristic properties of the detection of IR signals and images by frequency conversion to the visible and subsequent detection by a photocathode device are described. The way in which phase-matching normally restricts the spectral bandwidth to a few wavenumbers and the field of view to a few degrees is discussed. The conditions for achieving maximum image resolution are identified. Signal up-conversion should find application in the detection of weak IR radiation in astronomy and spectroscopy. Image up-conversion provides a novel “direct” method of viewing IR images. The ultimate temperature resolution when viewing a room temperature thermal scene is discussed.

Realization of a new type of birefringent filter.

Abstract: A birefringent filter based upon a new principle described in a theoretical paper by one of the authors has been constructed. The theory developed there has been verified experimentally in all respects. Limitatations on a filter of this type are discussed along with possible applications.

Nanosecond High Resolution Framing Camera

Abstract: A framing camera employing proximity focused image intensifiers with an effective frame rate of 108 frames/sec and a spatial resolution of greater than 10 line pairs/mm on the 25 mm diam photocathode has been constructed and tested. The camera consists of six proximity focused image intensifiers coupled in a hexagonal array. This array may be viewed by either a standard film camera or an image orthicon television camera for remote monitoring. Interframe duration is adjustable from overlapping to several times the frame duration. Frame duration is adjusted by changing the pulse width from the main pulse generator. The shuttering circuit demonstrates zero interframe jitter and accurately known interframe and frame durations. Tests indicate there is no physical reason this technique cannot be extended to equivalent frame rates of greater than 109 frames/sec using low resistance photocathodes.

A new scanning thermometer

Abstract: A new thermographic apparatus is described. Present infrared techniques have been employed together with a novel optical scanner and a calibrated electronic digital readout system to produce a fast scanning radiometer capable of reading black-body temperatures at the rate of 15000 values per second. The range covered is 27.8-37.4 degrees C in 0.2 deg C steps, or in simultaneous multiple isothermal increments of 1 deg C. The scanning time is 1 s for a field of view 37 cm*30 cm with a spatial resolution of 3 mm. The scanner is fixed focus with a depth of field of about +or-5 cm. The recording error due to mirror variations is less than 0.2 deg C and the noise equivalent temperature less still. A stability of 0.2 deg C has been achieved. The application of this instrument to the assessment of static thermal patterns and dynamic variations is discussed with particular reference to its potential value in medicine.

Holographic motion picture microscopy

Abstract: Holographic motion pictures provide a means for recording and observing transient, dynamic, small-scale events occurring at unpredictable times and locations in a given volume of space. Using an argon ion laser to generate repetitive pulses of 50 μs duration at a wavelength of 514.5 nm (5145 A), holographic movies of living marine plankton organisms were produced by recording a series of in-line holograms at 70 frames/s on 35 mm film. The reconstructed holographic images may be viewed with a standard microscope, photographed with a still camera, or copied with a conventional movie camera for subsequent projection. Image resolution of 10 μm was obtained.

Martian spectral reflectivity properties from Mariner 7 observations

Abstract: An analysis of data taken by the Mariner 6 and Mariner 7 spacecraft has been made in order to extend the knowledge of spectral reflectivity differences on the surface of Mars. The data were collected with the Mariner wide-angle television camera which utilizes a vidicon image tube as sensor. The data consist of a series of pictures taken through sequenced color filters with passbands in the visible region of the electromagnetic spectrum (0.43 - 0.65 microns). The Martian regions photographed lie in the longitude range 300° to 30° (East Longitude) and include the prominent dark areas Meridiani Sinus, Sabaeus Sinus, and Margeritifer Sinus, as well as the light 'desert' areas Moab, Thymiamata and Deucalionis Regio. It was necessary to remove harmonic noise from the television images in order to detect and measure significant spectral reflectivity differences in the equatorial regions of Mars. The resolution element near the center of the planetary disc was 30 km. by 200 km. The measurements represent an order of magnitude improvement in linear spatial resolution over previous measurements made with earth based telescopes and comparable broad band spectral resolution. No reliable published measurements exist for these regions of Mars but the new measurements showed a general agreement with the previous low resolution measurements of other parts of the planet. The colors of Martian features are very sensitive to the geometry of illumination and viewing. However, color differences attributable to geographic variations in the reflecting properties of the surface and/or atmosphere are recognized in an area near the center of the martian disc. The reflectivity ratio red/green for these areas is strongly correlated with the normal albedo but varies inversely as the reflectivity ratio blue/green. The spectral resolution of the system for measurements within the dark area Meridiani Sinus is limited by aliasing effects with small albedo features. The dependence of color on local geometry is investigated on the assumption that all the martian features in an area extending from 20°N to 30°S and from 310°E to 30°E have the same correlation between color and normal albedo when this is measured under standard illumination and viewing conditions. Models of a wavelength dependent photometric function and of a uniform atmospheric scattering layer are both consistent with the data. Atmospheric scattering alone can account for the local geometry effect but if the scattering layer is geographically uniform and independent of Martian local time the atmospheric optical depth is three times that predicted from ultraviolet reflectivity measurements. Near the center of the martian disc, three distinct reflectivity groups (D, L1 and L2) are recognized indicating the existence of abrupt transitions in reflectivity and extensive homogeneous areas with little variation in intrinsic reflectivity. These areas are identified and the boundaries between them studied using high resolution photography. The boundary between the areas with reflectivities D and L1, corresponds to a change in surface reflectivity. The boundary between the areas with reflectivities L1 and L2 corresponds to the edge of a cloud or haze layer. The reflectance properties of this layer are comparable to those which have been previously measured from limb photographs. Color-color plots and color-reflectivity plots for Martian surface areas show some similarities with the moon but significant differences. Martian light and dark areas cannot be explained as simply different polymers of carbon suboxide. It may be possible to match the reflectivity characteristics of both light and dark areas with oxidized basalt but if this is the case there must be a change in particle size as well as composition.

Information content of simulated space photographs as a function of various levels of image resolution.

Abstract: The results of research are reported on the information content in simulated space photographs derivable as a function of various levels of image resolution. Whenever certain resource features could not be consistently identified on simulated low-resolution imagery, attempts were made to define the required level of image resolution that would allow a skilled interpreter to discriminate one feature from another. The results of this research, conducted within a chaparral-hardwood-grassland environment in California, indicate that simulated ERTS data contain sufficient information to allow an interpreter to discriminate between woody vegetation, grassland, and water bodies. However, if more detailed information is desired, the imagery must have a ground resolution of at least 50 ft, showing shape, size, texture, and shadow characteristics within each vegetation type. Spaceborne data, therefore, often will have to be supplemented by higher resolution aircraft imagery, depending on the types of resource information being sought.

Direct Analysis of Spectra by Image Isocon and Computer

Abstract: Astronomical spectra are, with few exceptions, still being recorded on photographic emulsions. These generally have the advantages of better spatial resolution and larger available area than existing photoelectric imaging detectors. On the other hand they do suffer from a small dynamic range (15 or 20: 1), reciprocity failure, and a quantum efficiency of less than 1 per cent. Image intensifiers and image orthocons can be used to improve sensitivity, but where photographs are used for the record the other problems tend to remain. Calibration and extraction of the appropriate astronomical information in digital form involves a considerable amount of time and careful work, as one can appreciate from many of the papers presented at this colloquium.