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David M Kipping - One of the best experts on this subject based on the ideXlab platform.

  • binning is sinning morphological light curve distortions due to finite Integration Time
    Monthly Notices of the Royal Astronomical Society, 2010
    Co-Authors: David M Kipping
    Abstract:

    We explore how finite Integration Times or equivalently temporal binning induces morphological distortions to the transit light curve. These distortions, if uncorrected for, lead to the retrieval of erroneous system parameters and may even lead to some planetary candidates being rejected as ostensibly unphysical. We provide analytic expressions for estimating the disturbance to the various light-curve parameters as a function of the Integration Time. These effects are particularly crucial in light of the long-cadence photometry often used for discovering new exoplanets by, for example, Convection Rotation and Planetary Transits (CoRoT) and the Kepler Missions (8.5 and 30 min). One of the dominant effects of long Integration Times is a systematic underestimation of the light-curve-derived stellar density, which has significant ramifications for transit surveys. We present a discussion of numerical Integration techniques to compensate for the effects and produce expressions to quickly estimate the errors of such methods, as a function of Integration Time and numerical resolution. This allows for an economic choice of resolution before attempting fits of long-cadence light-curves. We provide a comparison of the short- and long-cadence light curves of TrES-2b and show that the retrieved transit parameters are consistent using the techniques discussed here.

  • binning is sinning morphological light curve distortions due to finite Integration Time
    arXiv: Earth and Planetary Astrophysics, 2010
    Co-Authors: David M Kipping
    Abstract:

    We explore how finite Integration Times or equivalently temporal binning induces morphological distortions to the transit light-curve. These distortions, if uncorrected for, lead to the retrieval of erroneous system parameters and may even lead to some planetary candidates being rejected as ostensibly unphysical. We provide analytic expressions for estimating the disturbance to the various light-curve parameters as a function of the Integration Time. These effects are particularly crucial in light of the long-cadence photometry often used for discovering new exoplanets by, for example, Convection Rotation and Planetary Transits (COROT) and the Kepler Mission (8.5 and 30 min). One of the dominant effects of long Integration Times is a systematic underestimation of the light-curve-derived stellar density, which has significant ramifications for transit surveys. We present a discussion of numerical Integration techniques to compensate for the effects and produce expressions to quickly estimate the errors of such techniques, as a function of Integration Time and numerical resolution. This allows for an economic choice of resolution before attempting fits of long-cadence light-curves. We provide a comparison of the short- and long-cadence light-curves of TrES-2b and show that the retrieved transit parameters are consistent using the techniques discussed here.

Ye Tian - One of the best experts on this subject based on the ideXlab platform.

  • Modeling and quantitative analysis of tropospheric impact on inclined geosynchronous SAR imaging
    2019
    Co-Authors: Dong Xichao, Hu Jiaqi, Hu Cheng, Long Teng, Li Y., Ye Tian
    Abstract:

    Geosynchronous orbit synthetic aperture radar (GEO SAR) has a long Integration Time and a large imaging scene. Therefore, various nonideal factors are easily accumulated, introducing phase errors and degrading the imaging quality. Within the long Integration Time, tropospheric status changes with Time and space, which will result in image shifts and defocusing. According to the characteristics of GEO SAR, the modeling, and quantitative analysis of background troposphere and turbulence are conducted. For background troposphere, the accurate GEO SAR signal spectrum, which takes into account the Time-varying troposphere, is deduced. The influences of different rates of changing (ROC) of troposphere with Time are analyzed. Finally, results are verified using the refractive index profile data from Fengyun (FY) 3C satellite and the tropospheric zenith delays data from international GNSS service (IGS). The Time-space changes of troposphere can cause image shifts which only depend on the satellite beam-foot velocity and the linear ROC of troposphere. The image defocusing is related to the wavelength, resolution requirement, and the second and higher orders of ROC. The short-wavelength GEO SAR systems are more susceptible to impacts, while L-band GEO SAR will be affected when the Integration Time becomes longer. Tropospheric turbulence will cause the amplitude and phase random fluctuations resulting in image defocusing. However, in the natural environment, radio waves are very weakly affected by turbulence, and the medium-inclined GEO SAR of L- to C-band will not be affected, while the Xband will be influenced slightly

  • Modeling and quantitative analysis of tropospheric impact on inclined geosynchronous SAR imaging
    'MDPI AG', 2019
    Co-Authors: Dong Xichao, Hu Jiaqi, Hu Cheng, Long Teng, Li Y., Ye Tian
    Abstract:

    Geosynchronous orbit synthetic aperture radar (GEO SAR) has a long Integration Time and a large imaging scene. Therefore, various nonideal factors are easily accumulated, introducing phase errors and degrading the imaging quality. Within the long Integration Time, tropospheric status changes with Time and space, which will result in image shifts and defocusing. According to the characteristics of GEO SAR, the modeling, and quantitative analysis of background troposphere and turbulence are conducted. For background troposphere, the accurate GEO SAR signal spectrum, which takes into account the Time-varying troposphere, is deduced. The influences of different rates of changing (ROC) of troposphere with Time are analyzed. Finally, results are verified using the refractive index profile data from Fengyun (FY) 3C satellite and the tropospheric zenith delays data from international GNSS service (IGS). The Time-space changes of troposphere can cause image shifts which only depend on the satellite beam-foot velocity and the linear ROC of troposphere. The image defocusing is related to the wavelength, resolution requirement, and the second and higher orders of ROC. The short-wavelength GEO SAR systems are more susceptible to impacts, while L-band GEO SAR will be affected when the Integration Time becomes longer. Tropospheric turbulence will cause the amplitude and phase random fluctuations resulting in image defocusing. However, in the natural environment, radio waves are very weakly affected by turbulence, and the medium-inclined GEO SAR of L- to C-band will not be affected, while the Xband will be influenced slightly.Mathematical Geodesy and Positionin

  • demonstration experiments of geosynchronous sar focusing and interferometry using gnss satellites
    International Conference on Signal Processing, 2016
    Co-Authors: Xichao Dong, Ye Tian
    Abstract:

    Geosynchronous SAR (GEO SAR) has great potentials in Earth observation as its wide swath coverage and fine resolution. But the long Integration Time is a double-edged sword which will lead to the error accumulations and the resultant performance degradation. In this paper, 3 demonstration experiments are presented for validating GEO SAR focusing feasibility and interferometry under long Integration Time, and the ionospheric influences. The GNSS satellites, including the Beidou IGSO and GPS satellites, are employed as illuminators. The principles, configurations, data processing and analysis are given for the 3 experiments separately. The experiment results validate well that GEO SAR can focus well and measure surface height with a good accuracy.

  • theoretical analysis and verification of Time variation of background ionosphere on geosynchronous sar imaging
    IEEE Geoscience and Remote Sensing Letters, 2015
    Co-Authors: Ye Tian, Xichao Dong, Tao Zeng, Teng Long, Kuan Lin, Xinyu Zhang
    Abstract:

    Geosynchronous synthetic aperture radar (SAR) (GEO SAR) has the characteristic of long Integration Time; thus, the Time-freezing model assumption of background ionosphere for traditional low Earth orbit (LEO) SAR no longer holds in GEO SAR. Furthermore, the background ionosphere variation within the Integration Time cannot be omitted either. In this letter, the variation of total electron content within Integration Time is analyzed and described in detail by using polynomial approximation, and a new GEO SAR signal model influenced by background ionosphere is also proposed. In view of this novel model, the analytical expression of image shift and defocusing phase error are derived in the first place. Then, a quantitative analysis for the image shift and image defocusing in the range and azimuth directions is conducted, and the performance bounds of Time-varying parameters of background ionosphere effects on focusing are obtained. Finally, the U.S. Total Electron Content measured data are used to verify the theoretical results of background ionosphere effects on GEO SAR focusing.

John L Spiesberger - One of the best experts on this subject based on the ideXlab platform.

  • determining probability distribution of coherent Integration Time near 133 hz and 1346 km in the pacific ocean
    Journal of the Acoustical Society of America, 2013
    Co-Authors: John L Spiesberger
    Abstract:

    The hypothesis tested is that internal gravity waves limit the coherent Integration Time of sound at 1346 km in the Pacific ocean at 133 Hz and a pulse resolution of 0.06 s. Six months of continuous transmissions at about 18 min intervals are examined. The source and receiver are mounted on the bottom of the ocean with timing governed by atomic clocks. Measured variability is only due to fluctuations in the ocean. A model for the propagation of sound through fluctuating internal waves is run without any tuning with data. Excellent resemblance is found between the model and data's probability distributions of Integration Time up to five hours.

  • internal waves role in determining probability distribution of coherent Integration Time near 133 hz and 3709 km in north pacific ocean
    IEEE Journal of Oceanic Engineering, 2011
    Co-Authors: John L Spiesberger
    Abstract:

    The hypothesis tested is that internal gravity waves limit the coherent Integration Time of sound at 3709 km in the Pacific ocean at 133 Hz and a pulse resolution of 0.06 s. Five days of continuous transmissions at 2-min intervals are examined. The source and the receiver are mounted on the bottom of the ocean with timing governed by atomic clocks. Measured variability is only due to fluctuations in the ocean. A model for the propagation of sound through fluctuating internal waves is run without any tuning with data. Excellent resemblance is found between the model and data's probability distributions of Integration Time up to a day, which is the largest lag explored. The probability that the Integration exceeds a day or more is about 0.15. The model underpredicts the probability of occurrence of Integration Times shorter than 10 min. However, the overwhelming agreement at longer Times supports the conclusion that the standard spectrum of internal waves accurately explains almost all of the distribution of measured Integration Time.

  • internal waves role in determining probability distribution of coherent Integration Time near 133 hertz and 3709 kilometers in north pacific ocean
    Journal of the Acoustical Society of America, 2011
    Co-Authors: John L Spiesberger
    Abstract:

    The hypothesis tested is that internal gravity waves limit the coherent Integration Time of sound at 3709 km in the Pacific Ocean at 133 Hz and a pulse resolution of 0.06 s. Five days of continuous transmissions at 2 min intervals are examined. The source and receiver are mounted on the bottom of the ocean with timing governed by atomic clocks. Measured variability is only due to fluctuations in the ocean. A model for the propagation of sound through fluctuating internal waves is run without any tuning with data. Excellent resemblance is found between the model and data’s probability distributions of Integration Time up to a day, which is the largest lag explored. The probability that the Integration exceeds a day or more is about 0.15. The model under‐predicts the probability of occurrence of Integration Times less than 10 min. However, the overwhelming agreement at longer Times supports the conclusion that the standard spectrum of internal waves accurately explains almost all of the distribution of meas...

Gerard Lachapelle - One of the best experts on this subject based on the ideXlab platform.

  • Choosing the coherent Integration Time for Kalman filter-based carrier-phase tracking of GNSS signals
    GPS Solutions, 2011
    Co-Authors: Cillian O’driscoll, Mark G. Petovello, Gerard Lachapelle
    Abstract:

    Carrier phase–based positioning using Global Navigation Satellite System (GNSS) signals can provide cenTimeter-level accuracy; however, to do so requires robust, continuous tracking of the phase of the received signal. The phase-locked loop is typically the weakest link in GNSS signal processing, with frequent cycle slips and loss of lock occurring at lower signal-to-noise ratios. One way to improve the signal-to-noise ratio is to increase the coherent Integration Time; however doing so reduces the loop update rate, thereby degrading performance. This paper investigates this trade-off between sensitivity and loop update rate by investigation of the Kalman filter-based tracking loop. It is shown that it is possible to choose an optimal Integration Time for a given application. A relatively straightforward procedure is given to determine this optimal value. The results are confirmed through real-Time kinematic processing of live satellite signals.

  • impact of extended coherent Integration Times on weak signal rtk in an ultra tight receiver
    2008
    Co-Authors: Mark G. Petovello, Gerard Lachapelle
    Abstract:

    The use of an ultra-tight GPS/IMU Integration strategy has been proposed for carrier phase-based positioning in weak signal environments. The use of IMU-aided tracking allows the carrier tracking loop bandwidths to be narrowed, thereby improving the quality of the carrier phase measurements. To improve tracking sensitivity in GPS receivers it is common to increase the coherent Integration Time, thereby improving the quality of the measurements when the C/N0 is low. One of the major challenges associated with increasing the coherent Integration Time is the increased sensitivity to dynamics, a problem which is largely mitigated by the use of INS aiding. Therefore, it would seem possible that ultratight Integration coupled with longer coherent Integration Times could yield a viable solution to the problem of RTK positioning in weak signal environments.

F Rocca - One of the best experts on this subject based on the ideXlab platform.

  • nearly zero inclination geosynchronous sar mission analysis with long Integration Time for earth observation
    IEEE Transactions on Geoscience and Remote Sensing, 2014
    Co-Authors: Josep Ruizrodon, A Broquetas, Eduardo Makhoul, Andrea Monti Guarnieri, F Rocca
    Abstract:

    In this paper, the performance of a nearly zero inclination and low eccentricity geosynchronous synthetic aperture radar (GEOSAR) mission for midlatitude (30 $^{\circ}$ –60 $^{\circ}$ ) Earth observation is analyzed. The slow motion of such satellites with respect to the Earth's surface makes it necessary to consider long coherent combination of pulses during hours to reach the desired along-track resolution. A system based on moderate transmitted powers and antenna sizes is considered. The necessary sensitivity in such GEOSAR system is obtained from the accumulated energy of the raw data using a pulse repetition frequency above the Doppler bandwidth and a long Integration Time. Several issues as a result of the long acquisition, such as target and atmospheric phase screen decorrelation, speckle noise impact on the received signal, and satellite station-keeping requirements, are analyzed. The feasibility of such systems to be placed on a broadcasting communication satellite makes nearly zero inclination GEOSAR a low-cost alternative of current SAR missions.