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1. chinaXiv:201703.01177 [pdf]

Radial variations of outward and inward Alfvnic fluctuations based on Ulysses observations

Yang, L.; Lee, L. C.; Li, J. P.; Luo, Q. Y.; Kuo, C. L.; Shi, J. K.; Wu, D. J.
Subjects: Geosciences >> Space Physics

Ulysses magnetic and plasma data are used to study hourly-scale Alfv{\'e}nic fluctuations in the solar polar wind. The calculated energy ratio $R^2_{v_A}$(cal) of inward to outward Alfv{\'e}n waves is obtained from the observed Wal{\'e}n slope through an analytical expression, and the observed $R^2_{v_A}$(obs) is based on a direct decomposition of original Alfv{\'e}nic fluctuations into outward- and inward-propagating Alfv{\'e}n waves. The radial variation of $R^2_{v_A}$(cal) shows a monotonically increasing trend with heliocentric distance $r$, implying the increasing local generation or contribution of inward Alfv{\'e}n waves. The contribution is also shown by the radial increase in the occurrence of dominant inward fluctuations. We further pointed out a higher occurrence ($\sim 83\%$ of a day in average) of dominant outward Alfv{\'e}nic fluctuations in the solar wind than previously estimated. Since $R^2_{v_A}$(cal) is more accurate than $R^2_{v_A}$(obs) in the measurement of the energy ratio for dominant outward fluctuations, the values of $R^2_{v_A}$(cal) in our results are likely more realistic in the solar wind than previously estimated and than $R^2_{v_A}$(obs) in our results. The duration ratio $R_T$ of dominant inward to all Alfv{\'e}nic fluctuations increases monotonically with $r$, and is about two or more times that from {\it Voyager 2} observations at $r \geq 4$~AU. Finally, from the variation trend in our results, a higher (lower) occurrence rate is expected at $r < 1$~AU ($r > 4$~AU) for dominant outward Alfv{\'e}nic fluctuations, and opposite variations are expected for dominant inward fluctuations. Simultaneously, $R^2_{v_A}$(cal) and $R_T$ will be expected to be smaller at $r < 1$~AU and larger at $r > 4$~AU. These results reveal new qualitative and quantitative features of Alfv{\'e}nic fluctuations therein compared with previous studies and put constraints on modelling the variation of solar wind fluctuations.

submitted time 2017-03-31 Hits19555Downloads1281 Comment 0

2. chinaXiv:201703.00307 [pdf]

Estimating the Sea State Bias of Jason-2 Altimeter From Crossover Differences by Using a Three-Dimensional Nonparametric Model

Jiang, Maofei; Xu, Ke; Liu, Yalong; Wang, Lei
Subjects: Geosciences >> Space Physics

With a standard deviation as large as 2 cm, the sea state bias (SSB) has become the dominant source of error in satellite altimetry. The operational SSB correction models are two-dimensional (2-D) empirical (parametric or nonparametric) models based on the altimeter-measured wind speed (U) and significant wave height (SWH). However, these 2-D SSB models cannot entirely parameterize the range bias variability. The SSB uncertainty may be lowered through improved SSB models including additional measurable or predictable correlatives. This paper presents a method to estimate the SSB from crossover differences by using a three-dimensional (3-D) nonparametric model. The model is based on U, SWH from Jason-2 altimeter ocean observations, and the mean wave period from the European Centre for Medium-Range Weather Forecasts reanalysis project ERA-Interim (The SSB model developed with the method presented in this paper is called “3-D SSB model” and the SSB estimated with the 3-D SSB model is called “3-D SSB estimate”). Simulations indicate that the wave period can greatly affect the SSB. Evaluated by the separate annual datasets from 2009 to 2011, the 3-D SSB estimates can increase the explained variance by 1.32 cm2, or 1.15-cm RMS relative to the traditional 2-D SSB estimates based on U and SWH. Spatial evaluation of improvement shows that the 3-D SSB estimates are better than the traditional 2-D SSB estimates at all latitudes. The enhancement from 2-D to 3-D SSB estimates is of great significance to improve the precision of the altimeter product.[COMP]: Please set math TYPE gin the sentence below (40) as per the authors PDF.

submitted time 2017-03-10 Hits16674Downloads1475 Comment 0

3. chinaXiv:201703.00306 [pdf]

Azimuth High Resolution for a Conically Scanned Pencil-Beam Scatterometer Using Rotating Azimuth Doppler Discrimination

Wang, Gang; Dong, Xiaolong; Zhu, Di; Bao, Qingliu
Subjects: Geosciences >> Space Physics

In order to satisfy a relatively high resolution for the retrieval of snow water equivalent, an X/Ku-band dual-frequency full-polarized SCATterometer (DFPSCAT) onboard Water Cycle Observation Mission (WCOM) satellite is designed for high-resolution observations. However, given the following situations, the method called “rotating azimuth Doppler discrimination” is proposed, which can satisfy the resolution requirement and real-time processing: 1) the conically rotation rate of antenna is relatively fast; 2) the swath width is larger than 1000?km; and 3) day or night observation capabilities are required. Considering the complexity of the system's design and the improvement of azimuth resolution capability, a burst pulsing scheme is addressed to satisfy the numbers of azimuth sampling. The simulation model is used to analyze the feasibility of azimuth discrimination method based on geometry and system parameters. It is shown that the achievable azimuth resolution is about 2–5?km at far end of the swath and only 5km at near end of the swath. The results show that when the size of a slice is set as 2–5?km, the Kpcis about less than 0.4 as snow depth varies, and the Kpcof combined slices is smaller than a single slice.

submitted time 2017-03-10 Hits15912Downloads1392 Comment 0

4. chinaXiv:201703.00300 [pdf]

Design of X/Ku dual-band dual-linear polarization reflectarray using double parallel dipole elements

Xue, Fei; Wang, Hongjian; Yi, Min
Subjects: Geosciences >> Space Physics

Two single-layer X/Ku dual-band dual-polarization reflectarray antennas of different sizes with double parallel dipole elements are presented. Elements of the two bands are set to two orthogonal linear polarizations and placed in interlaced grid. The proposed reflectarrays operate in two frequency-bands within X-band centered at 10 GHz and Ku-band centered at 13.58 GHz. The smaller size reflectarray with elements arranged in a 13 ?13 grid for X-band and in a 12 ?12 grid for Ku-band is designed and simulated first. Based on the excellent dual-band performance of the small size reflectarray, then a larger size prototype has been designed, manufactured and measured. Measured results demonstrate the maximum gain of 28.54 dB with 50.93% aperture efficiency at 10 GHz and 31.06 dB with 51.34% aperture efficiency at 13.58 GHz, which show desirable dual-band dual-polarization radiation performance.

submitted time 2017-03-10 Hits3182Downloads824 Comment 0

5. chinaXiv:201703.00298 [pdf]

A deblurring method for dynamic target observation of the geostationary interferometric microwave sounder (GIMS)

Zhang, Ying; Liu, Hao; Wu, Ji; Zhang, Cheng; He, Jieying
Subjects: Geosciences >> Space Physics

Brightness temperature change of observation target in one imaging period will introduce image blur to the retrieved image of geostationary interferometric microwave sounder (GIMS), which uses rotating circular array to realize time-sharing sampling other than snap-shot to reduce system complexity but meanwhile resulting in a relatively long imaging period. In this paper, an interpolation method utilizing time sequence of visibilities collected by time-sharing sampling is presented. The method is verified through a simulation system that simulates GIMS's observation process in viewing a series of near real case brightness temperature maps modeled by FNL/WRF/RTTOV method. Results show that the interpolation method can de-blur the image and reduce imaging error to the degree of snap-shot imaging. ?2016 IEEE.

submitted time 2017-03-10 Hits2072Downloads855 Comment 0

6. chinaXiv:201703.00296 [pdf]

Single-layer broadband linearly polarized reflectarray antenna by using phase-delay lines

Han, Chunhui; Zhang, Yunhua; Yang, Qingshan
Subjects: Geosciences >> Space Physics

In this paper, a novel X-band broadband single-layer unit cell with attached phase-delay lines for reflectarray antennas is proposed to surmount the limitation of the reflectarray bandwidth. The unit cell is composed of three circular rings, each with a pair of gaps which are mutually placed orthogonally, and two identical circular phase-delay lines are attached to the outer ring to provide the required reflection phase. After the simulation for the unit cell carried out, a large reflecting phase range of about 600?and almost linear phase curve are achieved at the center frequency of 10 GHz. Parallel phase curves of different frequencies ranging from 9 GHz to 12 GHz are also obtained. To validate the broadband performance of the proposed unit cell, a 9 ?9 center-fed reflectarray antenna operating at X band is designed and simulated. Simulation results show that the designed antenna has 34% 1-dB gain bandwidth, which demonstrates that an obvious improvement on the bandwidth has been achieved compared to the previous works. Besides, the cross-polarization level is decreased to -40 dB by a mirror symmetric element arrangement.

submitted time 2017-03-10 Hits4994Downloads887 Comment 0

7. chinaXiv:201703.00295 [pdf]

A broadband reflectarray using patch with slot ring on ground plane elements

Xue, Fei; Wang, Hongjian; Yi, Min; Dong, Xingchao
Subjects: Geosciences >> Space Physics

A broadband center-fed reflectarray antenna is presented in this paper. Patch with slot ring on ground plane elements are used for bandwidth improvement. It is shown that quasi-linear phase responses with broad frequency band can be achieved by such a phasing element. An 11?1 elements reflectarray is designed and simulated. The results show that the simulated gain is 23.92 dB at the center frequency of 13.58 GHz with 3-dB bandwidth of 52%, which demonstrate significant broadband operation compared with that of conventional reflectarray.

submitted time 2017-03-10 Hits1956Downloads843 Comment 0

8. chinaXiv:201703.00290 [pdf]

Deconvolution method for resolution enhancement of Dual-Frequency Polarized Scatterometer

Liu, Liling; Dong, Xiaolong; Zhu, Jintai; Zhu, Di
Subjects: Geosciences >> Space Physics

Dual-Frequency Polarized Scatterometer (DFPSCAT) is a new system utilizing Doppler beam sharpening (DBS) technology for azimuthal resolution enhancement. Considering the DBS technology is inapplicable for the middle areas of the swath, a theoretical framework of deconvolution signal processing is proposed to improve resolution. A deconvolution method of the nonlocally centralized sparse representation (NCSR) is adopted to verify its feasibility, and simulation results show that the deconvolution method have obviously better resolution enhancement and higher recovery accuracy than these of the classical scatterometer image reconstruction (SIR) method. ?2016 IEEE.

submitted time 2017-03-10 Hits2439Downloads883 Comment 0

9. chinaXiv:201703.00288 [pdf]

Inter-element phase self-calibration for GIMS (geostationary interferometric microwave sounder)

Han, Donghao; Liu, Hao; Wu, Ji; Zhang, Cheng
Subjects: Geosciences >> Space Physics

The inter-element phase calibration plays an important role in the overall calibration scheme for synthetic aperture radiometer. The traditional relative phase calibration approach is to use correlated noise injection network, which will be difficult to be implemented in millimeter wave band due to the complexity of the waveguide divider network. A novel self-calibration method for interferometric radiometers with rotating thinned array, especially for the geostationary interferometric microwave sounder(GIMS), has been proposed in this paper. By using this approach, neither dedicated hardware nor dedicated calibration working model is needed to achieved the relative phase calibration. The self-calibration approach is inherently merged with the nominal observation working model of GIMS, thanks to the continuous array rotating of GIMS instrument. A running average scheme has been introduced into the self-calibration approach to enhance the SNR of the calibration data, which is normally very low with the natural earth scene. The method is demonstrated by both simulation and field imaging experiment. ?2016 IEEE.

submitted time 2017-03-10 Hits1443Downloads832 Comment 0

10. chinaXiv:201703.00287 [pdf]

Passive submillimeter-wave imaging demonstrated by a two-element interferometer

Han, Dong-Hao; Liu, Hao; Zhang, De-Hai; Meng, Jin; Zhao, Xin; Zhang, Ying; Wu, Ji
Subjects: Geosciences >> Space Physics

In this paper, an SMMW interferometric radiometer concept is demonstrated by a two-element interferometer with dedicated high accuracy SMMW devices. Point-source calibration method is introduced in order to reduce instrument errors. Interference fringes and point target images are presented by this SMMW interferometer. The linear phase error of the interference fringes is less than 2?and the angular resolution is better than 0.57? The measured performance characteristics of the two-element interferometer are consistent with the theoretical analysis. This interferometer demonstrates a new method for passive SMMW remote sensing. ?2016, Science Press. All right reserved.

submitted time 2017-03-10 Hits1577Downloads923 Comment 0

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