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1. chinaXiv:201810.00187 [pdf]

Application and verification of simultaneous determination of cellulose ?13C and ?18O in Picea shrenkiana tree rings from northwestern China using the high-temperature pyrolysis method

XU Guobao; LIU Xiaohong; SUN Weizhen; CHEN Tuo; ZHANG Xuanwen; ZENG Xiaomin; WU Guoju; WANG Wenzhi; QIN Dahe
Subjects: Geosciences >> History of Geosciences

Stable isotopes in tree-ring cellulose provide important data in ecological, archaeological, and paleoenvironmental researches, thereby, the demand for stable isotope analyses is increasing rapidly. Simultaneous measurement of cellulose ?13C and ?18O values from tree rings would reduce the cost of isotopic commodities and improve the analytical efficiency compared with conventional separate measurement. In this study, we compared the ?13C and ?18O values of tree-ring ?-cellulose from Tianshan spruce (Picea schrenkiana) in an arid site in the drainage basin of the Urumqi River in Xinjiang of northwestern China based on separate and simultaneous measurements, using the combustion method (at 1050°C) and the high-temperature pyrolysis method (at 1350°C and 1400°C). We verified the results of simultaneous measurement using the outputs from separate measurement and found that both methods (separate and simultaneous) produced similar ?13C values. The two-point calibrated method improved the results (range and variation) of ?13C and ?18O values. The mean values, standard deviations, and trends of the tree-ring ?13C obtained by the combustion method were similar to those by the pyrolysis method followed by two-point calibration. The simultaneously measured ?18O from the pyrolysis method at 1400°C had a nearly constant offset with that the pyrolysis method at 1350°C due to isotopic-dependence on the reaction temperature. However, they showed similar variations in the time series. The climate responses inferred from simultaneously and separately measured ?13C and ?18O did not differ between the two methods. The tree-ring ?13C and ?18O values were negatively correlated with standardized precipitation evapotranspiration index from May to August. In addition, the ?18O was significantly correlated with temperature (positive), precipitation (negative), and relative humidity (negative) from May to August. The tree-ring ?13C and ?18O values determined simultaneously through the high-temperature pyrolysis method could produce acceptable and reliable stable isotope series. The simultaneous isotopic measurement can greatly reduce the cost and time requirement compared with the separate isotopic measurement. These results are consistent with the previous studies at humid sites, suggesting that the simultaneous determination of ?13C and ?18O in tree-ring ?-cellulose can be used in wide regions.

submitted time 2018-10-29 From cooperative journals:《Journal of Arid Land》 Hits3506Downloads807 Comment 0

2. 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 Hits1451Downloads836 Comment 0

3. 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 Hits1585Downloads925 Comment 0

4. chinaXiv:201612.00205 [pdf]

HY-2A Radar Altimeter Ultra Stable Oscillator Drift Estimation using Reconstructive Transponder with its Validation by Multi-mission Cross-Calibration

Junzhi Wan; Wei Guo; Fei Zhao; Caiyun Wang; Peng Liu
Subjects: Geosciences >> Space Physics

The paper presents a method estimating the HY-2A altimeter ultra stable oscillator (USO) drift with a reconstructive transponder. The frequency of the USO of the in-orbit altimeter changes with age, and a bias between the actual frequency and the nominal one exists. The USO bias contributes a portion of the altimeter range drift. The HY-2A altimeter transmits signals at a fixed time interval during calibration, and the actual interval between adjacent altimeter transitions, which is controlled by the USO, is different from the nominal one due to the USO drift. The reconstructive transponder measures the arrival times of the altimeter transmitted signals accurately with the atomic clock. The drift of the USO on-board the HY-2A altimeter can be estimated accurately by using the ranges from the reconstructive transponder and the HY-2A altimeter. The USO drifts of around 40 cm/year are presented. Furthermore, the multi-mission crosscalibration provides preliminary validation of HY-2A altimeter USO drift.

submitted time 2016-12-26 Hits2046Downloads719 Comment 0

5. chinaXiv:201612.00202 [pdf]

HY-2A Altimeter Time Tag Bias Estimation Using Reconstructive Transponder

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

Independent clocks provide time tags for the precision orbit determination (POD) equipment and the radar altimeter onboard the HY-2A satellite, and a bias between POD data' time tag and corresponding range observation's time tag from the HY-2A altimeter exists. The time tag bias contributes a bias in the sea surface height observation due to the nonzero time rate of change of the HY-2A altimeter's height. A transponder for in-orbit radar altimeter calibration provides an approach to estimate the time tag bias. The altimeter receives the responding signals from the transponder and generates ranges. Pertinent reference ranges are obtained fromthe POD data and the transponder's coordinate. Using the ranges from the radar altimeter and the reference ranges, the time tag bias between the POD data and the altimeter observations can be estimated. During an in situ HY-2A altimeter calibration campaign using a reconstructive transponder from August 9, 2012, to July 20, 2014, 17 estimations of the altimeter's time tag bias were obtained. The preliminary results are presented in this letter.

submitted time 2016-12-26 Hits1974Downloads746 Comment 0

6. chinaXiv:201612.00197 [pdf]

A Matching Method for Establishing Correspondence between Satellite Radar Altimeter Data and Transponder Data Generated during Calibration

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

This letter presents a method for matching satellite radar altimeter data and transponder data generated during in situ calibration. The transponder generates a measurement error when it measures the arrival time of the altimeter’s transmitted signal and embeds the error in both the transponder’s recorded data and the altimeter’s recorded data. The secondorder finite difference sequence of this error sequence can be extracted from the raw data, thus, the correspondence between two identical but mismatched second-order difference sequences can be uniquely established. The measurement error is utilized,and a data matching method that can uniquely establish the correspondence between the altimeter’s recorded data sequence and the transponder’s recorded data sequence is presented.This post-processing method does not increase the real-time signal processing workload of the transponder. Furthermore,The principles underlying this method can be used for any transponder that can adjust the response signal delay during calibration.

submitted time 2016-12-26 Hits1634Downloads588 Comment 0

7. chinaXiv:201605.00287 [pdf]


Xu, Xi-Yu; Hua, Shen; Ke, Xu
Subjects: Geosciences >> Space Physics

GNSS buoys are innovative ocean instruments, and can provide calibrations of the sea surface height and significant wave height (SWH) products of satellite altimeters. This paper investigated the principles of the wave retrieval by GNSS buoys, and proposed a method of calibration of altimeter SWH product by GNSS buoys. The error sources in the calibration procedure were analyzed. Ocean calibration campaigns were implemented to measure the SWH at the HY-2 altimeter nadir points, and acquired a SWH bias of +7.92 +/- 5.04 cm using four-parameters retracking algorithm. The SWH bias was +20.37 +/- 12.79 cm base on the HY-2 operational SWH products. The calibration campaigns showed that, GNSS buoys could serve for the satellite altimeter SWH calibration under low sea state condition, and the four-parameters retracking algorithm outperformed the conventional three-parameters retracking algorithm in accuracy and consistency, at least for SWH retrieving.

submitted time 2016-05-03 Hits780Downloads424 Comment 0

8. chinaXiv:201605.00286 [pdf]


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 Hits1070Downloads620 Comment 0

9. chinaXiv:201605.00285 [pdf]


Xu, Xi-Yu; Ke, Xu; Hua, Shen; Wang, Zhen-Zhan; Liu, Ya-Long
Subjects: Geosciences >> Space Physics

An airborne delay Doppler altimeter was flown in autumn 2014. A calibration suite including a GNSS buoy, two tide gauges and two GPS stations were established. An experiment was carried out to test the GNSS buoy as a whole under dynamic ocean condition, to validate its performance and accuracy via the inter-comparison of tide gauges, and to demonstrate the altimetry calibration methods and to estimate the altimeter system bias. This paper presented some methods and results. The GNSS buoy system was proven to have the ability of measuring the sea surface height within 1cm, and the altimeter system bias had a consistency of centimeter level.

submitted time 2016-05-03 Hits637Downloads391 Comment 0

10. chinaXiv:201605.00283 [pdf]


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

Target brightness temperature maps can be used in geostationary interferometric microwave sounder (GIMS) system simulation. System simulation with accurate target brightness temperature maps can evaluate system performance in near real case and thus help adjust design parameters for the sensor before it is finally put into use. In this paper, method of simulating target brightness temperature using Weather Research and Forecasting Model and Radiative Transfer for TOVS (RTTOV) has been discussed. Target brightness temperature simulation results at oxygen absorption band and water-vapor absorption band have been presented. Some preliminary analyses of simulated brightness temperature for GIMS' observation have also been given.

submitted time 2016-05-03 Hits1194Downloads758 Comment 0

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