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Results for “modulation transfer function”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Ultraviolet proximity focussed converters for use in a satellite SEC-TV system.

Performance characteristics of Bendix type BX08025-4522 proximity-focussed vacuum-ultraviolet to visible-light image converters are presented. The converters are to be used with SEC vidicons as detectors for an echelle spectrograph on the International Ultraviolet Explorer astronomical satellite. Magnesium fluoride input windows with Cs-Te photocathodes are used in the converters, with P-11 phosphors on the fiber optic output windows. Quantum efficiencies, modulation transfer function, background, geometric distortion, and environmental test results are presented for the wavelength region from 1150 to 3500 A.-

Feibelman, W. A.↗
NASA NTRS1973

Feasibility test of a solid state spin-scan photo-imaging system

The feasibility of using a solid-state photo-imaging system to obtain resolution imagery from a Pioneer-type spinning spacecraft in future exploratory missions to the outer planets is discussed. Evaluation of the photo-imaging system performance, based on electrical video signal analysis recorded on magnetic tape, shows that the signal-to-noise (S/N) ratios obtained at low spatial frequencies exceed the anticipated performance and that measured modulation transfer functions exhibited some degradation in comparison with the estimated values, primarily owing to the difficulty in obtaining a precise focus of the optical system in the laboratory with the test patterns in close proximity to the objective lens. A preliminary flight model design of the photo-imaging system is developed based on the use of currently available phototransistor arrays. Image quality estimates that will be obtained are presented in terms of S/N ratios and spatial resolution for the various planets and satellites. Parametric design tradeoffs are also defined.

Laverty, N. P.↗
NASA NTRS1973

SEC vidicon testing

Results obtained from several basic measurements of the performance of an SEC vidicon camera head are presented. The measurements or tests are patterned around the sensor requirements which exist for a rapid response coronagraph. Following a brief description of the SEC vidicon camera head, test set-up, and operating procedures, results are presented for five basic tests. These tests include: (1) Input-output, or transfer, characteristics; (2) modulation transfer function; (3) signal-to-noise ratio; (4) photocathode sensitivity; and (5) target gain. The input-output characteristics and photocathode sensitivity measurements were obtained for three bandpasses centered about 4000, 5250, and 6200 A. Results are also given for the variation of photocathode sensitivity with position on the cathode surface.

Johnson, D. S., Jr.↗
NASA NTRS1973

The large space telescope

The large scale telescope (LST) intended as a permanent international facility to be placed in near earth orbit to perform astronomical observations, is discussed. The basic elements of the LST are detailed, and the modulation transfer function is presented. Both basic and special instruments are dealt with. The sensor parameters are listed, and the choice of the SEC Vidicon is justified.

Sobieski, S.↗
NASA NTRS1974

Scanning thermal plumes

In order to study the behavior and effects of thermal plumes associated with the condenser cooling of power plants, thermal line scans are periodically made from aircraft over all power plants along the Wisconsin shore of Lake Michigan. Simultaneous ground truth is also gathered with a radiometer. Some sequential imagery has been obtained for periods up to two hours to study short term variations in the surface temperature of the plume. The article concentrates on the techniques used to analyze thermal scanner data for a single power plant which was studied intensively. The calibration methods, temperature dependence of the thermal scanner, and calculation of the modulation transfer function for the scanner are treated. It is concluded that obtaining quantitative surface-temperature data from thermal scanning is a nontrivial task. Accuracies up to plus or minus 0.1 C are attainable.

Scarpace, F. L.↗
NASA NTRS1975

Balance between resolution and signal-to-noise ratio in scanner design for earth resources systems

An outline is presented of a method in which a sensor under design can be evaluated by comparison with an existing sensor of similar spectral response, providing certain performance characteristics are known. An approach for calculating errors in radiance measurements is discussed, giving attention to calibration, error caused by resolution factors, noise effects on accuracy, and combined radiance level accuracies for several scanner designs. The derivation of error caused by the modulation transfer function is also considered.

Norwood, V. T.↗
NASA NTRS1975

IPL processing of the Mariner 10 images of Mercury

This paper describes the digital processing performed on the images of Mercury returned to earth from Mariner 10. Each image contains considerably more information than can be displayed in a single picture. Several specialized processing techniques and procedures are utilized to display the particular information desired for specific scientific analyses: radiometric decalibration for photometric investigations, high-pass filtering to characterize morphology, modulation transfer function restoration to provide the highest possible resolution, scene-dependent filtering of the terminator images to provide maximum feature discriminability in the regions of low illumination, and rectification to cartographic projections to provide known geometric relationships between features. A principal task was the construction of full disk mosaics as an aid to the understanding of surface structure on a global scale.

Soha, J. M.↗
NASA NTRS1975

Scanning thermal plumes

Over a three-year period 800 thermal line scans of power plant plumes were made by an airborne scanner, with ground truth measured concurrently at the plants. Computations using centered finite differences in the thermal scanning imagery show a lower bound in the horizontal temperature gradient in excess of 1.6 C/m. Gradients persist to 3 m below the surface. Vector plots of the velocity of thermal fronts are constructed by tracing the front motion in successive thermal images. A procedure is outlined for the two-point ground calibration of a thermal scanner from an equation describing the scanner signal and the voltage for two known temperatures. The modulation transfer function is then calculated by input of a thermal step function and application of digital time analysis techniques using Fast Fourier Transforms to the voltage output. Field calibration tests are discussed. Data accuracy is limited by the level of ground truth effort chosen.

Scarpace, F. L.↗
NASA NTRS1976

Vidicon intensifier

Computer-designed sensor, consisting of single-stage electrostatically-focused, triode image intensifier, provides high quality imaging characterized by exceptionally low geometric distortion, low shading, and high center-and-corner modulation transfer function.

Carpentier, R. P.↗
NASA NTRS1976

Development of InSb charge-coupled infrared imaging devices: Linear imager

The following results were accomplished in the development of charge coupled infrared imaging devices: (1) a four-phase overlapping gate with 9 transfers (2-bits) and 1.0-mil gate lengths was successfully operated, (2) the measured transfer efficiency of 0.975 for this device is in excellent agreement with predictions for the reduced gate length device, (3) mask revisions of the channel stop metal on the 8582 mask have been carried out with the result being a large increase in the dc yield of the tested devices, (4) partial optical sensitivity to chopped blackbody radiation was observed for an 8582 9-bit imager, (5) analytical consideration of the modulation transfer function degradation caused by transfer inefficiency in the CCD registers was presented, and (6) for larger array lengths or for the insertion of isolated bits between sensors, improvements in InSb fabrication technology with corresponding decrease in the interface state density are required.

Phillips, J. D.↗
NASA NTRS1979

Spatial-frequency response of the limb infrared monitor of the stratosphere

Measurements from the Limb Infrared Monitor of the stratosphere (LIMS) are presented and discussed. From the LIMS design model data, the modulation transfer function (MTF) was calculated for the optical system, the detector field mask, the electronics, and the overall system for each channel. The signal output performance of the instrument was predicted from the system MTF data and model input radiance data for each channel. The MTF measurements made on the flight sensor confirmed the analytical results.

Wilson, R. G.↗
NASA NTRS1978

The modulation of the radar backscattering cross section by long ocean waves

The modulation transfer function which relates the backscattered microwave power to the long ocean wave field was measured in the North Sea during JONSWAP 75. Results from this tower experiment with an X-band scatterometer are presented and compared with the two-scale wave model (relaxation-time model).

Alpers, W.↗
NASA NTRS1979

Apodization and image contrast

Apodization is often defined in a restricted sense as the suppression of the outer parts (i.e., the concentric rings) of wave optical point images, which results in a higher relative concentration of energy in the central image area. In a wider sense, apodization is defined as any modification of the transmission distribution across the aperture. Generally the modulation transfer function (MTF) is not used in the treatment of apodization. To see how the imaging performance is modified, the MTF is introduced into the discussion. Besides the constant transmission, two transmission distributions which are functions of the aperture radius are considered.

Tschunko, H. F. A.↗
NASA NTRS1980

Cycle II.5 aircraft aero-optical turbulent boundary-layer/shear-layer measurements

The aero-optical effects associated with propagating a laser beam through aircraft turbulent boundary layers and shear layers were examined. Observed laser optical performance levels were compared with those inferred from aerodynamic measurements of unsteady densities and correlation lengths within these random flows. Optical instrumentation included a fast shearing interferometer (FSI). A 9 cm diameter collimated helium neon laser beam made a double pass through the aircraft random flow via an airfoil mirror located one meter from the fuselage. Typical aircraft turbulent boundary layer thickness measured 0.3 meters. Averaging many FSI generated modulation transfer functions (MTFs) and Fourier transforming, this average yields the expected far field intensity degradation associated with an aircraft mounted laser system. Aerodynamic instrumentation included fine wire probes to measure unsteady temperature and mass flux. A laser doppler velocimeter measured unsteady velocity within the flows. An analysis of these data yielded point measurements of unsteady density and correlation length.

Gilbert, K.↗
NASA NTRS1980

Lensless scanning telescope

A lensless scanning telescope composed of two circular apertures and having good response with minimum aliasing is described. By analogy with an arrangement of two slits, the modulation transfer function (MTF) of this telescope is derived. The MTF of a lensless telescope scanning the earth's surface from 500-km orbit is developed for both the scan and cross-scan directions. Response of 48% or better at 100-km wavelength in both directions is shown with aliasing errors due to sampling of 1% or less.

Edwards, H. B.↗
NASA NTRS1980

Voyager image processing at the Image Processing Laboratory

This paper discusses new digital processing techniques as applied to the Voyager Imaging Subsystem and devised to explore atmospheric dynamics, spectral variations, and the morphology of Jupiter, Saturn and their satellites. Radiometric and geometric decalibration processes, the modulation transfer function, and processes to determine and remove photometric properties of the atmosphere and surface of Jupiter and its satellites are examined. It is exhibited that selected images can be processed into 'approach at constant longitude' time lapse movies which are useful in observing atmospheric changes of Jupiter. Photographs are included to illustrate various image processing techniques.

Jepsen, P. L.↗
NASA NTRS1981

An industrial perspective of the LANDSAT opportunity

The feasibility of enhancing LANDSAT products to provide the greatest usability low cost data possible can be determined through government sponsorship and finance of one or more task forces composed of a critical number of experts in multiple disciplines from many industries and academia. The synergism of multiple minds addressing singular problems without the creation of permanent or perpetual structures must yield output in the form of implementable specifications, even if presented as alternatives. Changes are needed within the spacecraft in order to account for Sun angle changes. The use of pointing accuracy to make geometric corrections (and possible radiometric corrections, is needed more than onboard data reduction and information extraction, which assume a proper knowledge of application and reduce potential utilization. Multilinear arrays need to be investigated and methods for sensor calibration and for determining the effects of atmospheric inversion, as well as the best way to back out the modulation transfer function must be determined.

Williams, B. F.↗
NASA NTRS1981

Radiance profile enhancement for solar occultation measurements

It is pointed out that distortions in received signals in solar occultation measurements made from space derive from the systematic motion of the electrooptical sensor. In a wide range of cases, the motion-related signal distortions brought about by the instrument's full modulation transfer function are as important as those from the optics. It is shown through simulation that existing techniques in the field of digital-image processing can be applied directly to solar occultation experiments to correct for these distortions. The resulting enhanced radiation profile is found to be much closer to the true radiance profile than is the sampled output of the instrument.

Gomberg, R. I.↗