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  • Other Sources  (12)
  • 1990-1994  (12)
  • 1
    Publication Date: 2011-08-24
    Description: Terrain height variations in mountainous areas cause problems in radiometric corrections of synthetic aperture radar (SAR) images. To determine the elevation angle and the height at the different parts of an image, an application of the monopulse principle is proposed. From the ratios of images radiometrically modulated by the difference and sum antenna pattern in range it is possible to calculate the appropriate elevation angle at any point in the image. Design considerations for a corresponding airborne SAR-system are presented, and some estimates of error influences (e.g., ambiguities), expected performance and precision in topographic mapping are given.
    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. 302-304.
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  • 2
    Publication Date: 2011-08-24
    Description: The advantages and disadvantages of three different approaches to solving the problem of the radiometric correction of synthetic aperture radar (SAR) images of varying terrain heights are presented. The first approach involves registration of a digital elevation model (DEM) of the terrain to the image, determination of the local elevation and incidence angles, and appropriate radiometric correction. The second approach uses a DEM generated from interferometric SAR data to derive the elevation and incidence angle maps. In the third approach, a monopulse technique is employed to determine the elevation angle only. The relative errors in radiometric correction between these approaches are assessed. Calibration errors are estimated using corner reflectors deployed within some of the scenes imaged by the Jet Propulsion Laboratory airborne SAR (JPL AIRSAR).
    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. 271-273.
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  • 3
    Publication Date: 2011-08-24
    Description: As Synthetic Aperture Radar (SAR) system performance and experience in SAR signature evaluation increase, quantitative analysis becomes more and more important. Such analyses require an absolute radiometric calibration of the complete SAR system. To keep the expenditure on calibration of future multichannel and multisensor remote sensing systems (e.g., X-SAR/SIR-C) within a tolerable level, data from different tracks and different sensors (channels) must be cross calibrated. The 1989 joint E-SAR/DC-8 SAR calibration campaign gave a first opportunity for such an experiment, including cross sensor and cross track calibration. A basic requirement for successful cross calibration is the stability of the SAR systems. The calibration parameters derived from different tracks and the polarimetric properties of the uncalibrated data are used to describe this stability. Quality criteria for a successful cross calibration are the agreement of alpha degree values and the consistency of radar cross sections of equally sized corner reflectors. Channel imbalance and cross talk provide additional quality in case of the polarimetric DC-8 SAR.
    Keywords: AIRCRAFT INSTRUMENTATION
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 31; 1; p. 237-245.
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  • 4
    Publication Date: 2011-08-24
    Description: The POLCAL crosstalk removal algorithm is based on the statistical properties of the image background and does not need any corner reflector or active radar calibrator deployed in the scene. The advantage of being able to remove the crosstalk contamination without using external calibration targets gives rise to the consideration of algorithms based on clutter statistics in polarimetric synthetic aperture radar (SAR) images in more detail. The basic assumption of the POLCAL procedure is the decorrelation of copolarized and cross-polarized backscatter, which is valid for natural targets with azimuthal symmetry. This assumption and others regarding the properties of the imaged surface are examined. An improved version called POLCALII is presented, and its performance is compared with POLCAL.
    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. 2 (A93-47551 20-43); p. 1171-1173.
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  • 5
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    In:  Other Sources
    Publication Date: 2013-08-29
    Description: Results from the 1989 Airborne Synthetic Aperture Radar (SAR) Calibration Campaign at the DLR test site in Oberpfaffenhofen are presented. Passive corner reflectors were used to derive the receiver and transmitter distortion matrices and the absolute calibration factor of the multispectral polarimetric DC-8 SAR from the complex high resolution data. A basic requirement for cross-calibration of data from different tracks is the stability of the SAR system. The polarimetric properties of the uncalibrated data were used to describe this stability. Quality criteria for a successful polarimetric calibration were provided by the channel balance and cross-talk parameters.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL, Proceedings of the Third Airborne Synthetic Aperture Radar (AIRSAR) Workshop; p 147-156
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  • 6
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    In:  Other Sources
    Publication Date: 2019-01-25
    Description: Terrain height variations in mountainous areas cause two problems in the radiometric correction of SAR images: the first being that the wrong elevation angle may be used in correcting for the radiometric variation of the antenna pattern; the second that the local incidence angle used in correcting the projection of the pixel area from slant range to ground range coordinates may vary from that given by the flat earth assumption. We propose a novel design of a SAR system which exploits the monopulse principle to determine the elevation angle and thus the height at the different parts of the image. The key element of such a phase monopulse system is an antenna, which can be divided into a lower and upper half in elevation using a monopulse comparator. In addition to the usual sum pattern, the elevation difference pattern can be generated by a -pi phase shift on one half of the antenna. From the ratios of images radiometrically modulated by the difference and sum antenna pattern in cross-track direction, we can derive the appropriate elevation angle at any point in the image. Together with the slant range we can calculate the height of the platform above this point using information on the antenna pointing and the platform attitude. This operation, repeated at many locations throughout the image, allows us to build up a topographic map of the height of the aircraft above each location. Inversion of this map, using the precisely determined aircraft altitude and the accurate flight path, leads to the actual topography of the imaged surface. The precise elevation of one point in the image could also be used to convert the height map to a topographic map. In this paper, we present design considerations for a corresponding airborne SAR system in X-Band and give estimates of the error due to system noise and azimuth ambiguities as well as the expected performance and precision in topographic mapping.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: gress In Electromagnetics Research Symposium (PIERS); p 256
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  • 7
    Publication Date: 2019-07-12
    Description: High-accuracy absorption spectroscopy of CH3OH in the far infrared is discussed. In addition to 22 transitions in the ground state, the frequency of the (n, tau, J, K), (0, 1, 16, 8) to (0, 2, 15, 7) transition in the nu5 excited vibrational level, which is responsible for the laser emission at 119 microns, was measured. The measured frequency is 2,522,782.57(10) MHz at zero pressure, with a pressure shift of 6.1(32) kHz/Pa (0.805/420/ MHz/torr). An accurate remeasurement of the laser emission frequency has also been performed, and the results are in good agreement.
    Keywords: LASERS AND MASERS
    Type: IEEE Journal of Quantum Electronics (ISSN 0018-9197); 26; 575-579
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  • 8
    Publication Date: 2019-07-12
    Description: The frequencies of 26 laser lines with wavelengths between 57 and 534 microns are measured in the optically pumped laser gases CH3OD and N2H4. A pair of 12CO2 lasers are employed as a frequency standard for the heterodyne frequency measurements. As the measurements are oriented toward spectroscopic applications of FIR lasers where dense, broad, frequency coverage is essential, every strong pump absorption of the two molecules for new lines that might be made to lase by varying the laser gas pressure and the tuning of the pump laser are investigated.
    Keywords: LASERS AND MASERS
    Type: International Journal of Infrared and Millimeter Waves (ISSN 0195-9271); 12; 1161-116
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  • 9
    Publication Date: 2019-07-12
    Description: Fine-structure splittings of atomic oxygen (O-16) in the ground state have been accurately measured using a tunable far-infrared spectrometer. The 3P0-3pl splitting is 2,060,069.09 (10) MHz, and the 3Pl-3P2 splitting is 4,744,777.49 (16) MHz. These frequencies are important for measuring atomic oxygen concentration in earth's atmosphere and the interstellar medium.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 371; L85
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  • 10
    Publication Date: 2019-07-12
    Description: A tunable far-infrared spectrometer has been used to observe the pure rotational spectrum of MgH in a DC discharge of H2 with magnesium. The frequencies of the hyperfine components of the N = 1 - 0 transition are predicted to an estimated accuracy of + or - 350 kHz, which should be sufficient for the astrophysical identification of this species.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 359; L65
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