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  • OCEANOGRAPHY  (8)
  • EARTH RESOURCES AND REMOTE SENSING  (3)
  • Key words. Robust fitting  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Robust estimation of systematic errors of satellite laser range (1999)
    Springer
    Journal of geodesy 73 (1999), S. 345-349 
    Details
    ISSN: 1432-1394
    Keywords: Key words. Robust fitting ; Systematic errors ; SLR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Methods for analyzing laser-ranging residuals to estimate station-dependent systematic errors and to eliminate outliers in satellite laser ranges are discussed. A robust estimator based on an M-estimation principle is introduced. A practical calculation procedure which provides a robust criterion with high breakdown point and produces robust initial residuals for following iterative robust estimation is presented. Comparison of the results from the least-squares method with those of the robust method shows that the results of the station systematic errors from the robust estimator are more reliable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001900050252
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    Paper (German National Licenses)
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  • 2
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    Accurate measurement of mean sea level changes by altimetric satellites (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A technique for monitoring changes in global mean sea levels using altimeter data from a well-tracked satellite is examined. The usefulness of this technique is evaluated by analyzing Seasat altimeter data obtained during July-September 1978. The effects of orbit errors, geoid errors, sampling intervals, tides, and atmosphere refraction on the calculation of the mean sea level are investigated. The data reveal that the stability of an altimeter can be determined with an accuracy of + or - 7 cm using globally averaged sea surface height measurements. The application of this procedure to the US/French Ocean Topography Experiment is discussed.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 11
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  • 3
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    Oceanographic results from analysis of ERS-1 altimetry (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Large scale dynamic ocean topography and its variations were observed using ERS-1 radar altimeter measurements. The altimeter measurements analyzed are primarily from the ESA ocean product (OPR02) and from the Interim Geophysical Data Records (IGDR) generated by NOAA from the fast delivery (FD) data during the ERS-1 35 day repeat orbit phase. The precise orbits used for the dynamic topography solution are computed using dual satellite crossover measurements from ERS-1 and TOPEX (Topology Ocean Experiment)/Poseidon (T/P) as additional tracking data, and using improved models and constants which are consistent with T/P. Analysis of the ERS-1 dynamic topography solution indicates agreement with the T/P solution at the 5 cm root mean square level, with regional differences as large as 15 cm tide gauges at the 8 to 9 cm level. There are differences between the ERS-1 OPR02 and IGDR determined dynamic topography solutions on the order of 5 cm root mean square. Mesoscale oceanic variability time series obtained using collinear analysis of the ERS-1 altimeter data show good qualitative agreement when compared with the T/P results.
    Keywords: OCEANOGRAPHY
    Type: ESA, Proceedings of the Second ERS-1 Symposium on Space at the Service of Our Environment, Volume 1; p 489-494
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  • 4
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    Evaluation of the Seasat altimeter time tag bias (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Two methods were used in analyses of Seasat altimeter data, aimed at the corroboration of an inherent altimeter microprocessor delay compensation value of -79.4 msec, which benefited from a global data distribution in the oceanic areas: (1) the crossover method, using altimeter data differenced at points where the Seasat ground track intersected with itself, and (2) the direct use of the altimeter data. Because the former method is independent of errors in the geoid model, it is considered the more reliable. For all crossover method results, the adopted value of -79.4 msec is within the bounds of the standard deviation associated with the estimates, of which -78.1 + or - 2.0 msec is considered the best representative.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Journal of Geophysical Research; 87; Apr. 30
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  • 5
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    Sequential filtering applied to the determination of tracking station locations (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The extended sequential filter has been applied to the problem of dynamically determining the geocentric coordinates of two laser satellite tracking stations. This filter provides significant advantages over the classical batch methods through (1) fewer iterations required for convergence, (2) wider radius of convergence, and (3) availability of the parameter estimate evolution. Processing the data sequentially readily identifies the data arcs required to minimize the effects of geopotential model errors. By means of the Smithsonian standard earth 2 and the Goddard earth model 1 geopotentials to reduce laser range observations of the Beacon Explorer-C satellite, it is demonstrated that a two-pass arc is optimal for estimating the height of one station and all coordinates of the second station while minimizing the effect of geopotential model error. These two-pass estimates are in good agreement with other determinations that utilize considerably more data as well as different satellites.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Journal of Geophysical Research; 80; Feb. 10
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  • 6
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    Accuracy assessment of the large-scale dynamic ocean topography from TOPEX/POSEIDON altimetry (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The quality of TOPEX/POSEIDON determinations of the global scale dynamic ocean topography have been assessed by determining mean topography solutions for successive 10-day repeat cycles and by examining the temporal changes in the sea surface topography to identify known features. The assessment is based on the analysis of TOPEX altimeter data cycles 1 through 36. Important errors in the tide model used to correct the altimeter data have been identified. The errors were reduced significantly by use of a new tide model derived with the TOPEX/POSEIDON measurements. Maps of the global 1-year mean topography, produced using four of the most accurate of the marine geoid, show that the largest error in the dynamic ocean topography show expected features, such as the known annual hemispherical sea surface rise and fall and the seasonal variability due to monsoon influence in the Indian Ocean. Changes in the sequence of 10-day topography maps show the development and propagation of an equatorial Kelvin wave in the Pacific beginning in December 1992 with a propagation velocity of approximately 3 m/s. The observations are consistent with observed changes in the equatorial trade winds, and with tide gauge and other in situ observations of the strengthening of the El Nino. Comparison of TOPEX-determine sea surface height at points near oceanic tide gauges shows agreement at the 4 cm root-mean-square (RMS) level over the tropical Pacific. The results show that the TOPEX altimeter data set can be used to map the ocean surface with a temporal resolution of 10 days and an accuracy which is insonsistent with traditional in situ methods for the determination of sea level variations.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; C12; p. 24,605-24,617
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  • 7
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    Determination of ocean tides from the first year of TOPEX/POSEIDON altimeter measurements (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An improved geocentric global ocean tide model has been determined using 1 year of TOPEX/POSEIDON altimeter measurements to provide corrections to the Cartwright and Ray (1991) model (CR91). The corrections were determined on a 3 deg x 3 deg grid using both the harmonic analysis method and the response method. The two approaches produce similar solutions. The effect on the tide solution of simultaneously adjusting radial orbit correction parameters using altimeter measurements was examined. Four semidiurnal (N(sub 2), M(sub 2), S(sub 2) and K(sub 2)), four diurnal (Q(sdub 1), O(sub 1), P(sub 1), and K(sub 1)), and three long-period (S(sub sa), M(sub m), and M(sub f)) constituents, along with the variations at the annual frequency, were included in the harmomnic analysis solution. The observed annual variations represents the first global measurement describing accurate seasonal changes of the ocean during an El Nino year. The corrections to the M(sub 2) constituent have an root mean square (RMS) of 3.6 cm and display a clear banding pattern with regional highs and lows reaching 8 cm. The improved tide model reduces the weighted altimeter crossover residual from 9.8 cm RMS, when the CR91 tide model is used, to 8.2 cm on RMS. Comparison of the improved model to pelagic tidal constants determined from 80 tide gauges gives RMS differences of 2.7 cm for M(sub 2) and 1.7 cm for K(sub 1). Comparable values when the CR91 model is used are 3.9 cm and 2.0 cm, respectively. Examination of TOPEX/POSEIDON sea level anomaly variations using the new tide model further confirms that the tide model has been improved.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; C12; p. 24,809-24,820
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  • 8
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    Sensitivity analysis of short-arc station coordinate determinations from range data (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The accurate determination of the geocentric coordinates of a tracking station is essential for most geodetic and geophysical satellite applications. Since most of these satellites are close to the earth, the geopotential model is a dominant source of error which significantly influences station coordinate determinations. Other sources, such as GM error and drag, also influence the accuracy of the station coordinate determination. One technique for reducing the effect of these errors is to use short-arcs consisting of a few passes of the satellite over the tracking station. This paper analyzes the sensitivity of short-arc station coordinate estimates to various errors in the physical model, to the number of observations, and to the station-satellite geometry using simulated as well as real data.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Journal of the Astronautical Sciences; 24; Apr
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  • 9
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    Gravity model development for TOPEX/POSEIDON: Joint gravity models 1 and 2 (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The TOPEX/POSEIDON (T/P) prelaunch Joint Gravity Model-1 (JGM-1) and the postlaunch JGM-2 Earth gravitational models have been developed to support precision orbit determination for T/P. Each of these models is complete to degree 70 in spherical harmonics and was computed from a combination of satellite tracking data, satellite altimetry, and surface gravimetry. While improved orbit determination accuracies for T/P have driven the improvements in the models, the models are general in application and also provide an improved geoid for oceanographic computations. The postlaunch model, JGM-2, which includes T/P satellite laser ranging (SLR) and Doppler orbitography and radiopositioning integrated by satellite (DORIS) tracking data, introduces radial orbit errors for T/P that are only 2 cm RMS with the commission errors of the marine geoid for terms to degree 70 being +/- 25 cm. Errors in modeling the nonconservative forces acting on T/P increase the total radial errors to only 3-4 cm root mean square (RMS), a result much better than premission goals. While the orbit accuracy goal for T/P has been far surpassed geoid errors still prevent the absolute determination of the ocean dynamic topography for wavelengths shorter than about 2500 km. Only a dedicated gravitational field satellite mission will likely provide the necessary improvement in the geoid.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; C12; p. 24,421-24,447
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  • 10
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    Determination of the ocean circulation using Geosat altimetry (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A spherical harmonic model of the sea surface topography complete to degree and order 10 and a model of the earth's geopotential field complete to degree and order 50 have been obtained in a simultaneous solution using Geosat altimeter data and tracking data from 14 different satellites. The sea surface topography model compares well with oceanographic models computed using hydrographic data and ship drift data. Currently, errors in the estimated gravity field model limit the determination of the spherical harmonic coefficients of the general ocean circulation to degrees 10 and lower, corresponding to a minimum wavelength of 4000 km. Error analysis indicates that the correlation between the geoid and the sea surface topography model is less than 0.2, indicating good separation of the geoid and the sea surface topography at wavelengths of 4000 km or longer. Estimates of the scale factor for the significant wave height (H1/3), which is used to compute the electromagnetic bias correction and the bias for the Geosat altimeter, are obtained. The estimate of the H1/3 correction is 3.6 + or - 1.5 percent, and the height bias estimate is zero.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 3163-317
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