Performance evaluation of THz Atmospheric Limb Sounder (TALIS) of China

Wang, Wenyu; Wang, Zhenzhan; Duan, Yongqiang

doi:10.5194/amt-13-13-2020

Cited by 20 publications

(8 citation statements)

References 42 publications

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“…Due to the weak intensities of pure rotational lines, THz spectroscopic monitoring of methane at atmospheric concentrations would prove serious difficulties even after a strong improvement of the spectrometers sensitivity. On the contrary, the THz trace gas detection of polar GHGs already proved its capability by the monitoring of N 2 O and O 3 in the stratosphere with the MLS and TALIS sounders [8,9]. These THz heterodyne receivers are able to determine atmospheric subppm concentration profiles in the submm-and in the mm-wave domains.…”

Section: Trace Gases Thz Measurements Of N 2 O and O 3 In An Atmospheric Simulation Chamber Equipped With A Chernin Type Multi-pass Cellmentioning

confidence: 99%

“…The MLS instrument monitors O 3 and N 2 O by measuring pure rotational lines in the mm-wave (240 GHz) and in the submm-wave (640 GHz) domains, respectively [8]. More recently, the National Space Science Center of the Chinese Academy of Sciences has developed a THz Atmospheric Limb Sounder (TALIS) for atmospheric vertical resolved profile observations: as for MLS/Aura, O 3 and N 2 O are the targeted GHGs and their rotational transitions are probed with four heterodyne radiometers (LO frequencies: 118 GHz, 190 GHz, 240 GHz and 643 GHz) and several FFT spectrometers of 2 GHz bandwidth with 2 MHz resolution [9]. With this instrument, they are able to retrieve the N 2 O and O 3 profiles with average precisions lower than 10% and 5% from 10 to 42 km and from 10 to 70 km altitude, respectively.…”

Section: Introductionmentioning

confidence: 99%

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Terahertz Rotational Spectroscopy of Greenhouse Gases Using Long Interaction Path-Lengths

et al. 2021

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Even if on-board mm-wave/THz heterodyne receivers have been developed to measure greenhouse gases (GHGs) atmospheric profiles, rotational spectroscopy rests under-exploited for their monitoring unlike IR rovibrational spectroscopy. The present study deals with the ability of THz spectroscopy using long interaction path-lengths for GHG laboratory investigations. High-resolution THz signatures of non-polar greenhouse molecules may be observed by probing very weak centrifugal distortion induced rotational transitions. To illustrate, new measurements on CH4 and CF4 have been carried out. For CH4, pure rotational transitions, recorded by cw-THz photomixing up to 2.6 THz in a White type cell adjusted to 20 m, have allowed to update the methane line list of atmospheric databases. Concerning CF4, Fabry-Perot THz absorption spectroscopy with a km effective pathlength was required to detect line intensities lower than 10−27 cm−1/(moleccm−2). Contrary to previous synchrotron-based FT-FIR measurements, the tetrahedral splitting of CF4 THz lines is fully resolved. Finally, quantitative measurements of N2O and O3 gas traces have been performed in an atmospheric simulation chamber using a submm-wave amplified multiplier chain coupled to a Chernin type multi-pass cell on a 200 m path-length. The THz monitoring of these two polar GHGs at tropospheric and stratospheric concentrations may be now considered.

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Section: Trace Gases Thz Measurements Of N 2 O and O 3 In An Atmospheric Simulation Chamber Equipped With A Chernin Type Multi-pass Cellmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Terahertz Rotational Spectroscopy of Greenhouse Gases Using Long Interaction Path-Lengths

et al. 2021

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“…In addition, the atmospheric absorption caused by water vapor at the top of troposphere in this band is small enough to effectively measure the ozone distribution at the top of the troposphere. The 643 GHz radiometer can measure the absorption lines of the lowest frequency of HCl; the strongest absorption lines of ClO; and the weak absorption lines of BrO, HO 2 and N 2 O [2]. The proposed characteristics of the TALIS instrument, which may be slightly modified in the future, are summarized in Table 1.…”

Section: Instrument Characteristicsmentioning

confidence: 99%

“…The THz limb sounder can not only provide a better vertical resolution, but also collect chemical composition information in a wide range of height, which is not affected by the day and night cycle [1]. Limb sounding is a particularly useful technique in stratospheric and mesospheric temperature and chemistry detection, and has great potential in global wind measurement of the middle and upper atmosphere [2]. Microwave limb sounding remotely measures atmospheric parameters by observing millimeter-and submillimeter-wavelength thermal emission as the instrument field of view (FOV) is scanned through the atmospheric limb from above.…”

Section: Introductionmentioning

confidence: 99%

Simulation of the Spectrum Response for the THz Atmosphere Limb Sounder (TALIS)

Duan

Wang

et al. 2020

Sensors

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The THz atmospheric limb sounder (TALIS) is a microwave radiometer developed by the National Space Science Center of the Chinese Academy of Sciences for the detection of atmospheric trace gases. The observation range of the instrument mainly focuses on the middle and upper atmosphere (10–100 km above the earth’s surface). The detection targets include the temperature, pressure, and more than 10 kinds of atmospheric components. Its scientific goal is to improve our comprehension of atmospheric chemical composition and dynamics, and to monitor environmental pollution and sources in the atmosphere. The TALIS instrument is composed of an antenna, superheterodyne radiometers, and digital fast Fourier transform (FFT) spectrometers. By measuring the atmospheric thermal radiance in the wide frequency band with 118, 190, 240, and 643 GHz as the center frequency, the required volume mixing ratio (VMR) of atmospheric chemical species can be obtained. This paper introduces the characteristics of the TALIS instrument, and establishes a simulation model for the TALIS spectrometer. Through a joint simulation with an atmosphere radiative transfer simulator (ARTS), the TALIS instrument performance is evaluated from the aspects of calibration, the imbalance of two sidebands, the spectrum resolution, and quantization. The simulation results show that the two-point calibration can well-restore the radiance spectrum of the scene target and remove the influence of the spectral response function (SRF); the double side band (DSB) receiver with a 2 MHz resolution can meet the sensitivity and spectrum resolution requirements. Finally, the sensitivity errors of different quantization bits are given by the simulation and the results show that at 8-bit, the sensitivity and its degradation ratio are 1.251 K and 1.036 at a 2 MHz spectrum resolution and 100 ms integration time, respectively.

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“…Fast Fourier Transform (FFT) spectrometers of 2 GHz bandwidth with 2 MHz resolution are used to improve the measurement performance. The observation performance of TALIS has been estimated in our previous study [24]. In this study, the impacts of the instrument uncertainties, calibration errors and a priori errors on the retrieval are estimated.…”

Section: Introductionmentioning

confidence: 99%

Preliminary Evaluation of the Error Budgets in the TALIS Measurements and Their Impact on the Retrievals

Wang

Duan

2020

Remote Sensing

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The THz Atmospheric Limb Sounder (TALIS) is a Chinese sub-millimeter limb sounder being designed by National Space Science Center of the Chinese Academy of Sciences to measure the temperature and chemical constituents vertically in the middle and upper atmosphere, with good precision and vertical resolution. This paper presents a simulation study that assesses the measurement errors and their impacts on the retrievals. Three error sources, including instrument uncertainties, calibration errors and a priori errors, are considered. The sideband weight uncertainty, the local oscillator, the pointing angle offsets and the measurement noise (NEDT), are considered as instrument uncertainties. Calibration errors consist of the hot target offset, the nonlinearity residual of the two-point calibration, use of the Rayleigh–Jeans (R–J) approximation and the choice of the antenna pattern. A priori profile errors of temperature, pressure and species are also considered. The results suggest that the antenna pattern mainly affects the retrievals in the troposphere. The NEDT is a major error source affecting all of the retrievals. The R–J approximation has a great impact upon the retrievals at 643 GHz, and should not be used. The local oscillator offset leads to an obvious error above 50 km. The effect of nonlinearity residuals cannot be neglected above 70 km. The impact of the sideband weight uncertainty and the hot target offset are relatively small. The pointing and the a priori errors can be neglected in most observation regions.

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Performance evaluation of THz Atmospheric Limb Sounder (TALIS) of China

Cited by 20 publications

References 42 publications

Terahertz Rotational Spectroscopy of Greenhouse Gases Using Long Interaction Path-Lengths

Terahertz Rotational Spectroscopy of Greenhouse Gases Using Long Interaction Path-Lengths

Simulation of the Spectrum Response for the THz Atmosphere Limb Sounder (TALIS)

Preliminary Evaluation of the Error Budgets in the TALIS Measurements and Their Impact on the Retrievals

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