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At least 109 records · Page 6

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NASA NTRS1976

Breadboard linear array scan imager using LSI solid-state technology

The performance of large scale integration photodiode arrays in a linear array scan (pushbroom) breadboard was evaluated for application to multispectral remote sensing of the earth's resources. The technical approach, implementation, and test results of the program are described. Several self scanned linear array visible photodetector focal plane arrays were fabricated and evaluated in an optical bench configuration. A 1728-detector array operating in four bands (0.5 - 1.1 micrometer) was evaluated for noise, spectral response, dynamic range, crosstalk, MTF, noise equivalent irradiance, linearity, and image quality. Other results include image artifact data, temporal characteristics, radiometric accuracy, calibration experience, chip alignment, and array fabrication experience. Special studies and experimentation were included in long array fabrication and real-time image processing for low-cost ground stations, including the use of computer image processing. High quality images were produced and all objectives of the program were attained.

Tracy, R. A.↗

NASA NTRS1975

Large format SEC orthicon integrating television sensor for LST

The Large Space Telescope will employ a 70 mm format SEC type television camera tube as the data sensor for one or more scientific instruments. The characteristics of this tube are described. The current performance is characterized by an MTF of 50% at 20 line pairs per mm and a signal-to-noise ratio that is about one-half the theoretical based on the square root of the number of photoelectrons. The paper presents some astronomical results and the status of the environmental testing of the tube. Other topics such as radiation sensitivity and thermal design are also discussed.

Lowrance, J. L.↗

NASA NTRS1977

DSN research and technology support

The ongoing activities at the Venus Station (DSS 13) and the Microwave Test Facility (MTF) discussed include: (1) equipment implementation for unattended operation at DSS 13; (2) salvaging of a 20-kW klystron, at a cost savings of several thousand dollars by the DSN High Power Transmitter Facility; (3) extensive tracking activities with the 26-m antenna including DSN Platform Parameters, Multistation Planetary Radar, Helios II Spectrum Broadening Analysis, VLBI Validation, Planetary Radio Astronomy, and Pulsar Rotation Constancy, for a total time of 219-1/4 observing hours; (4) clock synchronization transmissions from the DSS 13 master clock to the overseas 64-m antenna complexes and special implementation activities in support of PV-78; and (5) implementation of a hydrogen maser frequency standard and the pathfinder installation of a utility control system (UCS) and significant station modification and maintenance.

Jackson, E. B.↗

NASA NTRS1981

Thermal infrared array, phase 1. Volume 1: Technical

The recommended design configuration for the focal plane array of a 1,000 element linear pushbroom system consists of 32 modules; the complete configuration is built by butting together two 1024 linear arrays. Each of the linear arrays is formed by edge butting 16 modules together. By staggering the modules of the two rows, the channel outages which occur where the modules are edge butted can be eliminated. Two stages TDI operation is performed by the post processing electronics, which reduces the design complexity of the focal plane. Systems studies show that: (1) a single focal plane design can satisfy both the LEO and SEOS mission configurations; (2) available optical designs can meet mission goals; (3) MTF can be traded with optical complexity in a future study; (4) a chopping mechanism can be devised to modifying modulate radiation to a 4-inch focal plane as well as insert two calibration sources at the required frequencies for chopping and calibration; (5) radiative cooling technology should be suitable for a future sensor in either mission configuration; and (6) cold shielding is not a requirement.

Source record↗

NASA NTRS1982

Intagliated phosphor screen image tube project

The production and evaluation of a magnetic focus image tube for astronomical photography that has an intagliated phosphor screen is described. The modulation transfer function of such a tube was measured by electronic means and by film tests, and the results compared with tubes of more conventional construction. The physical properties of the image tube and film combination, the analytical model of the optical interface, and the salient features of the intagliated screen tube are described. The results of electronic MTF tests of the intagliated image tube and of the densitometry of the tube and film test samples are presented. It is concluded that the intagliated screen is a help, but that the thickness of the photographic film is also important.

Hertzel, R. J.↗

NASA NTRS1982

Low noise imaging photon counter for astronomy

The characteristics and performance of a Ranicon photon-counting system combined with digital tape recording are described. The most important features are a bialkali photocathode response over 256 X 256 digital pixels, with approximately 100 X 100 resolvable pixels at 50% MTF, a dead time of 16 microsec/count, a maximum recordable count rate of 14,400/sec, and a background of less than 1 count/digital pixel/h. A video cassette recorder serves for the digital recording which retains the temporal sequence of the registered photons. Astronomical applications will include low light level quantitative imaging and speckle imaging.

Mertz, L.↗

NASA NTRS1983

Investigation of several aspects of LANDSAT-4 data quality

No insurmountable problems in change detection analysis were found when portions of scenes collected simultaneously by LANDSAT 4 MSS and either LANDSAT 2 or 3. The cause of the periodic noise in LANDSAT 4 MSS images which had a RMS value of approximately 2DN should be corrected in the LANDSAT D instrument before its launch. Analysis of the P-tape of the Arkansas scene shows bands within the same focal plane very well registered except for the thermal band which was misregistered by approximately three 28.5 meter pixels in both directions. It is possible to derive tight confidence bounds for the registration errors. Preliminary analyses of the Sacramento and Arkansas scenes reveals a very high degree of consistency with earlier results for bands 3 vs 1, 3 vs 4, and 3 vs 5. Results are presented in table form. It is suggested that attention be given to the standard deviations of registrations errors to judge whether or not they will be within specification once any known mean registration errors are corrected. Techniques used for MTF analysis of a Washington scene produced noisy results.

Wrigley, R. C.↗

NASA NTRS1981

Information density and efficiency of two-dimensional /2-D/ sampled imagery

Information density and efficiency (i.e., the ratio of information density to data density) are used as criteria for assessing the quality of 2-D sampled and quantized imagery as a function of the statistical properties of random radiance fields, the spatial response (PSF or MTF) and sensitivity of imaging systems, and the sampling and quantization intervals. Computational results are intuitively satisfying: they are consistent with experimental and theoretical results obtained by earlier investigators concerned with the performance of TV cameras, and they provide useful guidelines for optimizing the design of line-scan and sensor-array imaging systems, especially if these systems use a digital communication link for transmitting data.

Huck, F. O.↗

NASA NTRS1984

Investigation of several aspects of LANDSAT-4 data quality

The Thematic Mapper scene of Sacramento, CA acquired during the TDRSS test was received in TIPS format. Quadrants for both scenes were tested for band-to-band registration using reimplemented block correlation techniques. Summary statistics for band-to-band registrations of TM band combinations for Quadrant 4 of the NE Arkansas scene in TIPS format are tabulated as well as those for Quadrant 1 of the Sacramento scene. The system MTF analysis for the San Francisco scene is completed. The thermal band did not have sufficient contrast for the targets used and was not analyzed.

Wrigley, R. C.↗

NASA NTRS1984

Thematic Mapper image quality - Registration, noise, and resolution

The Landsat-4 satellite has two new imaging radiometers, including the redesigned Multispectral Scanner (MSS) and the Thematic Mapper (TM). The present investigation is concerned with an assessment of TM image quality on the basis of a study of band-to-band registration, periodic noise, and spatial resolution. In the TM images analyzed, the band-to-band registration accuracy of the instrument is very good. A few imperfections were found. Once a stable misregistration is removed, the TM should also meet its registration specifications between focal planes. Spatial resolution analyses in terms of MTF were performed in comparison modes. The forward and backward scans were shown to have virtually identical MTFs.

Wrigley, R. C.↗

NASA NTRS1984

LANDSAT-4 Thematic Mapper Modulation Transfer Function (MFT) evaluation

The techniques used in the two-image comparison of TM data and 7-meter aerial data acquired over San Francisco on August 12, 1983 during LANDSAT 4 operation were refined. Analysis of one area is complete and reported herein; analysis of a second area is in progress. A large test target for measurement of the LANDSAT 5 MTF at the White Sands Missile Range, New Mexico was constructed.

Schowengerdt, R.↗

NASA NTRS1984

An investigation of several aspects of LANDSAT-5 data quality

Band-to-band registration, geodetic registration, interdector noise, and the modulation transfer function (MTE) are discussed for the Palmer County; TX scene. Band combinations for several LANDSAT 4 and LANDSAT 5 scenes; the geodetic registration test for the Sacramento, CA area; periodic noise components in TM band 5; and grey level measurements by detector for Great Salt Lake (UT) dark water forescans and backscans are considered. Results of MTF analyses of the San Mateo Bridge and of TM high resolution and aerial Daedalus scanner imagery are consistent and appear to be repeatable. An oil-on-sand target was constructed on the White Sands Missile Range in New Mexico. The two-image analysis procedure used is summarized.

Wrigley, R. C.↗

NASA NTRS1985

The atmospheric effect on the separability of field classes measured from satellites

The atmospheric effect on the upward radiance emerging from the atmosphere above a nonuniform surface results in a reduction of the separability between the surface classes by broadening the radiance probability distribution of each class, while narrowing the total radiance range. The atmospheric modulation transfer function (MTF) is used in Fourier transform analyses to simulate the atmospheric effect on the imagery of a nonuniform surface and to demonstrate the atmospheric effect on separability of field classes.

Kaufman, Y. J.↗

NASA NTRS1985

Performance evaluation and geologic utility of LANDSAT-4 thematic mapper data

The overall objective of the project was to evaluate LANDSAT-4 Thematic Mapper (TM) data in the context of geologic applications. This involved a quantitative assessment of the data quality including the spatial and spectral characteristics realized by the instrument. Three test sites were selected for the study: (1) Silver Bell, Arizona; (2) Death Valley, California; and (3) Wind River/Bighorn Basin area, Wyoming. Conclusions include: (1) Artificial and natural targets can be used to atmospherically calibrate TM data and investigate scanner radiometry, atmospheric parameters, and construction of atmospheric Modulation Transfer Functions (MTF's), (2) No significant radiometric degradation occurs in TM data as a result of SCROUNGE processing; however, the data exhibit narrow digital number (DN) distributiosn suggesting that the configuration of the instrument is not optimal for each science applications, (30 Increased spatial resolution, 1:24,000 enlargement capability, and good geometric fidelity of TM data allow accurate photogeologic/geomorphic mapping, including relative age dating of alluvial fans, measurement of structural and bedding attitudes, and construction of such things as structural cross sections and stratigraphic columns. (4) TM bands 5 and 7 are particularly useful for geologic applications because they span a region of the spectrum not previously sampled by multispectral scanner data and are important for characterizing clay and carbonate materials.

Paylor, E. D.↗

NASA NTRS1985

The Landsat sensor's spatial responses

Based on the geometrical characteristics of the Landsat-4 and Landsat-5 Thematic Mapper (TM) and Multispectral Scanner (MSS), functions defining their spatial responses are derived, i.e., transfer functions (TF's) and line-spread functions (LSF's). These design LSF's and TF's are modified based on prelaunch component and system measurements to provide improved estimates. The two MSS instruments were comparable at their temperatures of best focus; separate calculations were performed for bands 1 and 3, band 2, and band 4. The presample nadir effective instantaneous fields of view, based on the 0.5 modulation transfer function (MTF) criteria, are 70-75 m in the track direction and 79-82 m in the scan direction. For the TM instruments, more extensive prelaunch measurements were available. LSF's derived from component measurements differed from the limited measured LSF data only in the ringing response/overshoot behavior.

Markham, B. L.↗

NASA NTRS1988

Measurements of high degree solar oscillation amplitudes

Measurements of high degree solar oscillation velocity amplitudes corrected for the effects of atmospheric seeing are presented. Observations of high degree oscillations, which have very small spatial features, suffer from the effects of atmospheric image blurring and image motion, thereby reducing the amplitudes of their spatial frequency components. In an attempt to correct the velocity amplitudes for these effects, the atmospheric modulation transfer function (MTF) was measured simultaneously by looking at the effects of seeing on the solar limb. The peak velocity power decreases by 2.6 and the energy per mode decreases by a factor 5 as l increases from 200 to 700. The results suggest that the modes are not in energy equipartition with convective turbulent eddies in the top of the convection zone.

Kaufman, James M.↗

NASA NTRS1990

Sensor performance analysis

The theory is described and the equations required to design are developed and the performance of electro-optical sensor systems that operate from the visible through the thermal infrared spectral regions are analyzed. Methods to compute essential optical and detector parameters, signal-to-noise ratio, MTF, and figures of merit such as NE delta rho and NE delta T are developed. A set of atmospheric tables are provided to determine scene radiance in the visible spectral region. The Planck function is used to determine radiance in the infrared. The equations developed were incorporated in a spreadsheet so that a wide variety of sensor studies can be rapidly and efficiently conducted.

Montgomery, H. E.↗

NASA NTRS1991

Design and analysis of aspherical multilayer imaging X-ray microscope

Spherical Schwarzschild microscopes for soft X-ray applications in microscopy and projection lithography employ two concentric spherical mirrors that are configured such that the third-order spherical aberration and coma are zero. Based on incoherent, sine-wave MTF calculations, the object-plane resolution of a magnification-factor-20 microscope is presently analyzed as a function of object height and numerical aperture of the primary for several spherical Schwarzschild, conic, and aspherical two-mirror microscope configurations.

Shealy, David L.↗