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  • 1
    Electronic Resource
    Electronic Resource
    A linear spatio-temporal model of the light-to-bipolar cell system and its response characteristics to moving bars (1987)
    Springer
    Biological cybernetics 57 (1987), S. 357-363 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract A linear spatio-temporal model for the visual pathway from receptor to bipolar cell is presented. This model is based on histological and electrophysiological data obtained from previously published work. The model incorporates the salient linear spatio-temporal dynamic characteristics of the light-to-bipolar cell system, and aims at furthering our understanding of the integrated spatio-temporal response characteristics of this system. This model is used to examine the way spatial and temporal dynamic characteristics combine to form the response of a single bipolar and of a combination of two bipolars to a moving bar stimulus. A unimodal “speed sensitivity curve” is identified than can be used to postulate speed detection schemes based on simple thresholding operations. The dependence of this speed sensitivity curve on specific temporal and spatial parameters of the receptive field is studied, giving rise to some simple speed discrimination schemata.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00354981
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    Paper (German National Licenses)
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  • 2
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    A linear spatio-temporal model of the light-to-bipolar cell system and its response characteristics to moving bars (1987)
    Springer
    Details
    Publication Date: 1987-01-01
    Print ISSN: 0340-1200
    Electronic ISSN: 1432-0770
    Topics: Biology , Computer Science , Physics
    Published by Springer
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    PAPER CURRENT
  • 3
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    MOSK - AUTOMATED MOSAICKING ALGORITHM FOR GENERATION OF SPACEBORNE SAR IMAGE (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Spaceborne Synthetic Aperture Radar (SAR) images are useful for planetary mapping and Earth sciences investigations. However, swath widths rarely exceed 100 Kilometers, and images must be patched together to create a mosaic in order to analyze larger areas. The primary function of this program is to generate large digital mosaics of SAR imagery without manually marked tiepoints. MOSK can produce multiframe mosaics by combining images in the along-track, adjacent cross-track swaths, or ascending and descending passes. Geocoded map registered images, such as the ones produced by MAPJTC (NPO-17718), are required as input. The output is a geocoded mosaic on a standard map grid which permits easy registration with other geocoded data sets. Mosaicking of geocoded SAR imagery involves three steps. First, a match point is selected at the center of the overlapping area, then an image patch around the match point is extracted from both images and cross-correlation is done on this area. Then, images with their refined match points are merged together to form a mosaic. To handle the large data volume of overlapping intermediate stages, large mosaics are divided into equal size quadrants with each quadrant cut from an intermediate mosaic. The full mosaic can then be assembled from the individual quadrants. Finally, radiometric disparities at the image seams are smoothed by a "feathering" technique. The automatic mosaic system generates output with minimal operator interaction. However, manual tiepointing is required in cases of a large registration error or two images with smooth surfaces such as ocean images. MOSK is implemented on a DEC VAX 11/785 running VMS 4.5. Most subroutines are in FORTRAN, but three are in MAXL and one is in APAL. The program requires 1 Mb of memory and a Floating Point Systems AP-5210 array processor. The system memory usage is approximately 1000 pages and the requirement of page file size is 2000 blocks. MOSK was developed in 1988.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NPO-17586
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  • 4
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    MAPJTC- AN ALGORITHM FOR GENERATION OF GEOCODED DATA PRODUCTS FROM SPACEBORNE SAR IMAGERY (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: MAPJTC was designed to rectify and transform the standard image output of the digital Synthetic Aperture Radar (SAR) correlator into a geocoded map registered image without operator interaction or manual tiepointing. This is accomplished by modeling the distortions and predicting the pixel displacements based on platform and radar parameters. The map projection implemented in MAPJTC is the Universal Transverse Mercator. Since the re-sampling operation is independent of the transformation data generation, other cartographic projections can be implemented with few software modifications. MAPJTC makes a precise determination of the geodetic location of an arbitrary pixel within the image frame based on the simultaneous solution of a set of earth model equations, SAR Doppler equations, and SAR range equations that identify the slant range from the sensor to the target at a specific image pixel. Based on a table of geodetic coordinates of the image pixels, the image is then mapped onto the desired cartographic projection by applying the appropriate transformation equations. Typically, mapping involves a two-dimensional re-sampling and is very computationally intensive. MAPJTC reduces the procedure to two one-dimensional passes, which saves computer time. Geocoding transforms the rectified image into a grid defined by a specific map projection. (The image is rotated and rectified to match the map projection.) Again, the two dimensional re-sampling process can be separated into two one-dimensional re-sampling processes. Optionally, MAPJTC can correct terrain-induced distortions in SAR imagery when a digital elevation map is available. MAPJTC was developed on a DEC VAX 11/785 under VMS 4.5. The program is written in FORTRAN (84%), APAL (2%), and MAXL (14%). It requires 6Mb of memory and a Floating Point Systems AP-5210 Array Processor equipped with 1Mb of memory. MAPJTC can run interactively or as a batch job. MAPJTC was developed in 1987.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NPO-17418
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  • 5
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    Attitude steering for space shuttle based synthetic aperture radars (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A technique is presented to steer the antenna beam to the zero-Doppler line for a spacecraft platform which operates in a non-zero roll attitude. The purposes of employing this attitude steering technique are reduction of the Doppler centroid error caused by the variation in target elevation; reduction of the Doppler centroid bound; and reduction of the Doppler drift. It is shown that a fixed attitude sequence can be easily accommodated in the radar command sequence to achieve nearly zero-Doppler steering. Implementation of this technique improves the image quality as well as simplifies the processor design.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 297-301.
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  • 6
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    SAR processing based on the exact two-dimensional transfer function (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The two-dimensional transfer functions of several synthetic aperture radar (SAR) focusing algorithms are derived considering the spaceborne SAR environments. The formulation includes the factors of the earth rotation and the antenna squint angles. The resultant transfer functions are explicitly expressed in terms of Doppler centroid frequency and Doppler frequency rate, which can be accurately estimated from the SAR data. Point target simulation results show that the algorithm based on the two-dimensional Fourier transformation outperforms the one-dimensional one for processing data acquired from high squint angles. The two-dimensional Fourier transformation approach appears to be a viable and simple solution for the processor design of future spaceborne SAR systems.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 355-359.
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  • 7
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    Application of the multiple PRF technique to resolve Doppler centroid estimation ambiguity for spaceborne SAR (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Estimation of the Doppler centroid ambiguity is a necessary element of the signal processing for SAR systems with large antenna pointing errors. Without proper resolution of the Doppler centroid estimation (DCE) ambiguity, the image quality will be degraded in the system impulse response function and the geometric fidelity. Two techniques for resolution of DCE ambiguity for the spaceborne SAR are presented; they include a brief review of the range cross-correlation technique and presentation of a new technique using multiple pulse repetition frequencies (PRFs). For SAR systems, where other performance factors control selection of the PRF's, an algorithm is devised to resolve the ambiguity that uses PRF's of arbitrary numerical values. The performance of this multiple PRF technique is analyzed based on a statistical error model. An example is presented that demonstrates for the Shuttle Imaging Radar-C (SIR-C) C-band SAR, the probability of correct ambiguity resolution is higher than 95 percent for antenna attitude errors as large as 3 deg.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 30; 5; p. 941-949.
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  • 8
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    Ice tracking techniques, implementation, performance, and applications (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Present techniques of ice tracking make use both of cross-correlation and of edge tracking, the former being more successful in heavy pack ice, the latter being critical for the broken ice of the pack margins. Algorithms must assume some constraints on the spatial variations of displacements to eliminate fliers, but must avoid introducing any errors into the spatial statistics of the measured displacement field. We draw our illustrations from the implementation of an automated tracking system for kinematic analyses of ERS-1 and JERS-1 SAR imagery at the University of Alaska - the Alaska SAR Facility's Geophysical Processor System. Analyses of the ice kinematic data that might have some general interest to analysts of cloud-derived wind fields are the spatial structure of the fields, and the evaluation and variability of average deformation and its invariants: divergence, vorticity and shear. Many problems in sea ice dynamics and mechanics can be addressed with the kinematic data from SAR.
    Keywords: OCEANOGRAPHY
    Type: Advances in Space Research (ISSN 0273-1177); 12; 7; p. 141-147.
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  • 9
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    Doppler centroid estimation ambiguity for synthetic aperture radars (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A technique for estimation of the Doppler centroid of an SAR in the presence of large uncertainty in antenna boresight pointing is described. Also investigated is the image degradation resulting from data processing that uses an ambiguous centroid. Two approaches for resolving ambiguities in Doppler centroid estimation (DCE) are presented: the range cross-correlation technique and the multiple-PRF (pulse repetition frequency) technique. Because other design factors control the PRF selection for SAR, a generalized algorithm is derived for PRFs not containing a common divisor. An example using the SIR-C parameters illustrates that this algorithm is capable of resolving the C-band DCE ambiguities for antenna pointing uncertainties of about 2-3 deg.
    Keywords: COMMUNICATIONS AND RADAR
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  • 10
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    Squint mode SAR processing algorithms (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The unique characteristics of a spaceborne SAR (synthetic aperture radar) operating in a squint mode include large range walk and large variation in the Doppler centroid as a function of range. A pointing control technique to reduce the Doppler drift and a new processing algorithm to accommodate large range walk are presented. Simulations of the new algorithm for squint angles up to 20 deg and look angles up to 44 deg for the Earth Observing System (Eos) L-band SAR configuration demonstrate that it is capable of maintaining the resolution broadening within 20 percent and the ISLR within a fraction of a decibel of the theoretical value.
    Keywords: COMMUNICATIONS AND RADAR
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