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1. 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 Hits12741Downloads824 Comment 0

2. chinaXiv:201703.00289 [pdf]

Estimating the sea state bias of HY-2A radar altimeter by using a three-dimentional nonparametric model

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

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) nonparametric models based on the wind speed (U) and the significant wave height (SWH) that can be directly measured by the altimeters. This paper estimates the sea state bias of HY-2A radar altimeter using a three-dimensional (3-D) nonparametric model based on SWH from HY-2A interim geophysical dataset records (IGDR), U and the mean wave period (MWP) from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis project ERA-Interim. The 3-D SSB estimates can increase the explained variance by 1.72 cm2, or 1.31 cm RMS relative to the traditional 2-D SSB estimates based on U and SWH. �2016 IEEE.

submitted time 2017-03-10 Hits1167Downloads338 Comment 0

3. chinaXiv:201605.00286 [pdf]

DEVELOPMENT OF THE RECONSTRUCTIVE TRANSPONDER FOR IN-ORBIT CALIBRATION OF HY-2 ALTIMETER

Wang, Caiyun; Guo, Wei; Zhao, Fei; Wan, Junzhi; Xu, Ke
Subjects: Geosciences >> Space Physics

HY-2 satellite, the first ocean dynamic satellite of China, was launched in August 2011, carrying a dual frequency (Ku band and C band) altimeter, to measure the global mean sea level [1]. To provide truly sea level measurements, in-orbit calibration is essential. This paper concerns the transponder in-orbit calibration method. A signal reconstructive transponder for HY-2 altimeter in-orbit calibration is presented. Different from the existing bent-pipe ones, this kind of transponder can capture and track altimeter pulses, record them, and reconstruct the chirp pulses, transmit them back to the altimeter. It is carried on a SUV, reduces requirement for a permanent installation site. With the characteristics of capture and record altimeter signals, the HY-2 altimeter inner path delay and clock drift could be derived from the calibration data.

submitted time 2016-05-03 Hits496Downloads283 Comment 0

4. chinaXiv:201605.00284 [pdf]

THE ALTIMETER PRECISION COMPARISON BETWEEN SAR MODE AND CONVENTIONAL MODE THROUGH AIRBORNE EXPERIMENT

Xu, Ke; Liu, Peng; Shi, Lingwei; Wang, Lei; Yu, Xiufen
Subjects: Geosciences >> Space Physics

Compared with conventional radar altimeter (CRA), synthetic aperture radar altimeter (SARAL) is a new generation radar altimeter and has better height precision and spatial resolution. As using synthetic aperture technique, SARAL data processing is very different from CRA. To verify the performance and the processing algorithm, an airborne experimental system of SARAL is developed. The experimental system was installed in Y-12 aircraft, and a lot of data was obtained in the October 2014. The echo signal with SAR mode and conventional mode are obtained at the same time, so the standard deviations of the two modes are compared. The results indicate that the height precision of SARAL is improved about 1 times. The significant wave height value extracted from the SARAL waveform is very close to that of the buoy deployed at the experiment area.

submitted time 2016-05-03 Hits388Downloads256 Comment 0

5. chinaXiv:201605.00278 [pdf]

THE LATEST ASSESSMENT FOR THE REPROCESSED GDR PRODUCT OF HY-2A ALTIMETER

Liu, Yalong; Xu, Ke; Zhang, Youguang; Wang, Lei; Xu, Xiyu; Chen, Hua
Subjects: Geosciences >> Space Physics

This paper is aimed to assess the accuracy of HY-2A altimetry system. To further improve the accuracy and performance of HY-2A observed SSHs, several new treatments including 4 parameters maximum likelihood estimation (MLE4) retracking for Ku and C band, non-parameter sea state bias (NPSSB) model, and reprocessed dual-frequency altimeter ionospheric correction are included. The evaluation from dual-crossover comparison of the fully reprocessed level-2 sensor geophysical dataset records (SGDRs) data suggests that the algorithm and model improvements mentioned above give rise to remarkable promotion to the accuracy of the forthcoming version GDRs. In this study we conclude that the standard deviation of 5.79 cm is achieved from crossover comparison between HY-2A and Jason-2 sea surface height (SSHs), suggesting a promising situation of HY-2A altimetry datasets.

submitted time 2016-05-03 Hits504Downloads270 Comment 0

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