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  • Other Sources  (7)
  • 2000-2004  (7)
  • 1
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    Media Calibration in the Deep Space Network: A Status Report (2002)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: A new media calibration system (MCS) has been implemented at the Goldstone complex of the DSN (Deep Space Network). It is intended to calibrate the delay of radio signals imposed by the neutral atmosphere. The system provides periodic measurements of both the static dry and fluctuating wet components of this delay. In particular, the system will calibrate the fluctuations in line of sight path delay due to atmospheric water vapor that we believe will dominate the error budget for several radio science and radio astronomy experiments. We have compared two of these media calibration systems with a connected element interferometer on a 21 km baseline. In this report we describe a total of 30 observations in which a radio source was tracked for an hour or more and the delay residuals then calibrated using the MCS. The accuracy of the comparison appears to be limited by systematic errors in the interferometer, which are under investigation. However, our results do indicate that the MCS can meet or exceed the two-way Allan standard deviation specification of 1.5 x 10( exp -15) on time scales of 2,000 - 10,000 sec, as required by the Cassini GWE (Gravitational Wave Experiment) for two way Doppler tracking.
    Keywords: Geophysics
    Type: International VLBI Service for Geodesy and Astrometry General Meeting Proceeding; 194-198; NASA/CP-2002-210002
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  • 2
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    Calibration of Atmospherically Induced Delay Fluctuations Due to Water Vapor (2000)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: We have completed a new generation of water vapor radiometers (WVR), the A- series, in order to support radio science experiments with the Cassini spacecraft. These new instruments sense three frequencies in the vicinity of the 22 GHz emission line of atmospheric water vapor within a 1 degree beamwidth from a clear aperture antenna that is co-pointed with the radio telescope down to 10 degree elevation. The radiometer electronics features almost an order of magnitude improvement in temperature stability compared with earlier WVR designs. For many radio science experiments, the error budget is likely to be dominated by path delay fluctuations due to variable atmospheric water vapor along the line-of-sight to the spacecraft. In order to demonstrate the performance of these new WVRs we are attempting to calibrate the delay fluctuations as seen by a radio interferometer operating over a 21 km baseline with a WVR near each antenna. The characteristics of these new WVRs will be described and the results of our preliminary analysis will be presented indicating an accuracy of 0.2 to 0.5 mm in tracking path delay fluctuations over time scales of 10 to 10,000 seconds.
    Keywords: Meteorology and Climatology
    Type: International VLBI Service for Geodesy and Astrometry: 2000 General Meeting Proceedings; 274-279; NASA/CP-2000-209893
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  • 3
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    Development of a High-Stability Microstrip-based L-band Radiometer for Ocean Salinity Measurements (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The development of a microstrip-based L-band Dicke radiometer with the long-term stability required for future ocean salinity measurements to an accuracy of 0.1 psu is presented. This measurement requires the L-band radiometers to have calibration stabilities of less than or equal to 0.05 K over 2 days. This research has focused on determining the optimum radiometer requirements and configuration to achieve this objective. System configuration and component performance have been evaluated with radiometer test beds at both JPL and GSFC. The GSFC testbed uses a cryogenic chamber that allows long-term characterization at radiometric temperatures in the range of 70 - 120 K. The research has addressed several areas including component characterization as a function of temperature and DC bias, system linearity, optimum noise diode injection calibration, and precision temperature control of components. A breadboard radiometer, utilizing microstrip-based technologies, has been built to demonstrate this long-term stability.
    Keywords: Oceanography
    Type: IGARSS2004-130-11430 , 2004 IEEE Geoscience and Remote Sensing Symposium; Sep 20, 2004 - Sep 24, 2004; Anchorage, AK; United States
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  • 4
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    Prototype Development of a Geostationary Synthetic Thinned Aperture Radiometer, GeoSTAR (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Preliminary details of a 2-D synthetic aperture radiometer prototype operating from 50 to 58 GHz will be presented. The instrument is being developed as a laboratory testbed, and the goal of this work is to demonstrate the technologies needed to do atmospheric soundings with high spatial resolution from Geostationary orbit. The concept is to deploy a large sparse aperture Y-array from a geostationary satellite, and to use aperture synthesis to obtain images of the earth without the need for a large mechanically scanned antenna. The laboratory prototype consists of a Y-array of 24 horn antennas, MMIC receivers, and a digital cross-correlation sub-system. System studies are discussed, including an error budget which has been derived from numerical simulations. The error budget defines key requirements, such as null offsets, phase calibration, and antenna pattern knowledge. Details of the instrument design are discussed in the context of these requirements.
    Keywords: Communications and Radar
    Type: Earth Science and Technology Conference (ESTC); Jun 22, 2004 - Jun 24, 2004; Palto Alto, CA; United States
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  • 5
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    STAR Concept for Passive Microwave Temperature Sounding from Middle Earth Orbit (MeoSTAR) (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A future mission for a new microwave atmospheric temperature sounder radiometer in a Middle Earth Orbit (MEO) at 11,000 km altitude is described. The MeoSTAR design uses a stationary l-dimensional Synthetic Thinned Array Radiometer in the 50-60 GHz microwave sounding band, to provide a 'pushbroom' image as the satellite orbits. The advantage of this concept is an image with a high spatial resolution and a wide swath with no scanning antenna to disturb the visual and IR sensors on the same satellite.
    Keywords: Earth Resources and Remote Sensing
    Type: IEEE Geoscience and Remote Sensing Society (IGARSS); Sep 01, 2004; Anchorage, AK; United States
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  • 6
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    GeoSTAR - A Synthetic Aperture Microwave Sounder for Geostationary Missions (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR) is a new microwave atmospheric sounder under development. It will bring capabilities similar to those now available on low-earth orbiting environmental satellites to geostationary orbit - where such capabilities have not been available. GeoSTAR will synthesize the multimeter aperture needed to achieve the required spatial resolution, which will overcome the obstacle that has prevented a GEO microwave sounder from being implemented until now. The synthetic aperture approach has until recently not been feasible, due to the high power needed to operate the on-board high-speed massively parallel processing system required for 2D-synthesis, as well as a number of system and calibration obstacles. The development effort under way at JPL, with important contributions from the Goddard Space Flight Center and the University of Michigan, is intended to demonstrate the measurement concept and retire much of the technology risk.
    Keywords: Communications and Radar
    Type: SPIE 4th International Asia-Pacific Environmental Remote Sensing Symposium, Honolulu; Nov 08, 2004 - Nov 11, 2004; Honolulu, HI; United States
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  • 7
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    GeoSTAR - A Microwave Sounder for Geostationary Satellites (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: GeoSTAR represents a new approach to microwave atmospheric sounding that is now under development. It has capabilities similar to sensors currently operating on low earth orbiting weather satellites but is intended for deployment in geostationary orbit - where it will complement future infrared sounders and enable all-weather temperature and humidity soundings and rain mapping. The required spatial resolution of 50 km or better dictates an aperture of 4 meters or more at a sounding frequency of 50 GHz, which is difficult to achieve with a real aperture system - this is the reason why it has until now not been possible to put a microwave sounder on a geostationary platform. GeoSTAR is instead based on a synthetic aperture imaging approach. Among the advantages of such a system are that there are no moving parts, and the size of the aperture is easily expandable to meet future needs. A ground based prototype of GeoSTAR is currently under development in an effort led by the Jet Propulsion Laboratory.
    Keywords: Spacecraft Instrumentation and Astrionics
    Type: IEEE International Topical Meeting on Geoscience and Remote Sensing Symposium, IGARSS ''04; Sep 20, 2004 - Sep 24, 2004; Anchorage, AK; United States
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