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  • Communications and Radar  (3)
  • 2015-2019  (2)
  • 2005-2009  (1)
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  • 1
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    Novel Photon-Counting Detectors for Free-Space Communication (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present performance data for novel photon-counting detectors for free space optical communication. NASA GSFC is testing the performance of two types of novel photon-counting detectors 1) a 2x8 mercury cadmium telluride (HgCdTe) avalanche array made by DRS Inc., and a 2) a commercial 2880-element silicon avalanche photodiode (APD) array. We present and compare dark count, photon-detection efficiency, wavelength response and communication performance data for these detectors. We successfully measured real-time communication performance using both the 2 detected-photon threshold and AND-gate coincidence methods. Use of these methods allows mitigation of dark count, after-pulsing and background noise effects. The HgCdTe APD array routinely demonstrated photon detection efficiencies of greater than 50% across 5 arrays, with one array reaching a maximum PDE of 70%. We performed high-resolution pixel-surface spot scans and measured the junction diameters of its diodes. We found that decreasing the junction diameter from 31 micrometers to 25 micrometers doubled the e- APD gain from 470 for an array produced in the year 2010 to a gain of 1100 on an array delivered to NASA GSFC recently. The mean single-photon SNR was over 12 and the excess noise factors measurements were 1.2-1.3. The commercial silicon APD array exhibited a fast output with rise times of 300 ps and pulse widths of 600 ps. On-chip individually filtered signals from the entire array were multiplexed onto a single fast output.
    Keywords: Communications and Radar
    Type: GSFC-E-DAA-TN29653 , SPIE Photonics West; Feb 13, 2016 - Feb 18, 2016; San Francisco, CA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    GGOS working group on ground networks and communications (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Activities of this Working Group include the investigation of the status quo and the development of a plan for full network integration to support improvements in terrestrial reference frame establishment and maintenance, Earth orientation and gravity field monitoring, precision orbit determination, and other geodetic and gravimetric applications required for the long-term observation of global change. This integration process includes the development of a network of fundamental stations with as many co-located techniques as possible, with precisely determined intersystem vectors. This network would exploit the strengths of each technique and minimize the weaknesses where possible. This paper discusses the organization of the working group, the work done to date, and future tasks.
    Keywords: Communications and Radar
    Type: Dynamic Planet 2005 : Monitoring and Understanding a Dynamic Planet with Geodetic and Oceanographic Tools, a Joint Assembly of International Associations : IAG, IAPSO, and IABO; Aug 22, 2005 - Aug 26, 2005; Cairns; Australia
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Digital Beamforming Synthetic Aperture Radar Developments at NASA Goddard Space Flight Center (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Advanced Digital Beamforming (DBF) Synthetic Aperture Radar (SAR) technology is an area of research and development pursued at the NASA Goddard Space Flight Center (GSFC). Advanced SAR architectures enhances radar performance and opens a new set of capabilities in radar remote sensing. DBSAR-2 and EcoSAR are two state-of-the-art radar systems recently developed and tested. These new instruments employ multiple input-multiple output (MIMO) architectures characterized by multi-mode operation, software defined waveform generation, digital beamforming, and configurable radar parameters. The instruments have been developed to support several disciplines in Earth and Planetary sciences. This paper describes the radars advanced features and report on the latest SAR processing and calibration efforts.
    Keywords: Communications and Radar
    Type: GSFC-E-DAA-TN35269 , GSFC-E-DAA-TN36034 , 2016 IEEE International Symposium on Phased Array Systems and Technology; Oct 18, 2016 - Oct 21, 2016; Waltham, MA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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