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

Abstract

THz Atmospheric Limb Sounder (TALIS) is a microwave limb sounder being developed for atmospheric high precision observation by the National Space Science Center, Chinese Academy of Sciences (NSSC, CAS). It is designed to measure the temperature and chemical species such as O 3 , HCl, ClO, N 2 O, NO, NO 2 , HOCl, H 2 O, HNO 3 , HCN, CO, SO 2 , 10 BrO, HO 2 , H 2 CO, CH 3 Cl, CH 3 OH, and CH 3 CN with high vertical resolution from surface to about 100 km to improve our comprehension of atmospheric chemistry and dynamics, and to monitor the man-made pollution in the atmosphere. Four heterodyne radiometers including several FFT spectrometers of 2 GHz bandwidth with 2 MHz resolution are employed to obtain the atmospheric thermal emission in broad spectral regions centred near 118, 190, 240, and 643 GHz. A theoretical simulation is performed to estimate the retrieval precision of the main targets. Single scan measurement and averaged 15 measurement are considered in simulation, respectively. Temperature profile can be obtained with the precision of < 2K for a single scan from 15 to 85 km by using 118 GHz radiometer, and the 240 and 643 GHz radiometer can provide temperature information in the upper troposphere. Chemical species such as H 2 O, O 3 , HCl, N 2 O, and HNO 3 show high single scan retrieval precision of 1-50% at most altitudes. The other species should be retrieved by using averaged measurements because of the weak intensity or low abundance. 20 IntroductionHigh precision observation of the Earth's atmosphere is essential to the numerical weather prediction and climate change studies. The satellite can provide global coverage atmospheric monitoring in a short time. Instruments such as nadir microwave sounder and infrared sounder have been applied to measure the atmospheric temperature and humidity but with the poor vertical resolution and altitude range (Swadley et al., 2008). Terahertz limb sounder can not only provide the 25 temperature profile with better vertical resolution but gather information on chemical composition in a wide altitude range and independent of the day-night cycle. Microwave limb sounding is a particularly useful technique in detecting stratospheric and mesospheric temperature and chemistry, and also has large potential for global wind measurement in the middle and upper atmosphere (Ochiai et al., 2017). Bands selectionThe spectral bands of TALIS are selected with the following criterions: (1) maximizing the number of species which will exert a strong influence on atmospheric chemistry and dynamics, (2) necessary space between the passband, (3) trade-off between realizable bandwidth and resolution. TALIS covers most spectral bands of EOS MLS and extends them. The broader bandwidth, finer resolution, and lower noise of TALIS can provide higher retrieval precision and effective altitude 15 range compared with EOS MLS. More chemical species can be measured by TALIS, such as NO 2 , NO, H 2 CO, and SO 2 (normal concentration).The 118 GHz radiometer, covering the strong O 2 line at 118.75 GH...

MULTICHARME: a modified Chernin-type multi-pass cell designed for IR and THz long-path absorption measurements in the CHARME atmospheric simulation chamber

“…With the aim to characterize the performances of MULTICHARME, we have chosen nitrous oxide N 2 O as test molecule for three main reasons: (i) N 2 O is a powerful and very stable greenhouse gas which can be considered now as the dominant ozone-depleting substance emitted in the 21st century in our atmosphere (Ravishankara et al, 2009). The monitoring of its chemical activity during transport from the troposphere to the stratosphere is crucial to control the ozone depletion; (ii) N 2 O is actually monitored in the troposphere and in the stratosphere by probing its rovibrational IR and rotational THz transitions with sounders such as the infrared atmospheric sounding interferometer (IASI) (Clerbaux et al, 2009) or THz atmospheric limb sounder (TALIS) (Wang et al, 2020) respectively; (iii) the molecular rotational and rovibrational line parameters (line frequencies, line widths, line intensities) of N 2 O were measured and calculated from the mm-wave to the near-IR domains and are listed in the international spectroscopic databases such as JPL (Pickett et al, 1998) or HITRAN (Gordon et al, 2022).…”

MULTICHARME: A modified Chernin-type multi-pass cell designed for IR and THz long-path absorption measurements in the CHARME atmospheric simulation chamber

“…In the aim to characterize the performances of MULTICHARME, we have chosen nitrous oxide N2O as molecule test for three main reasons: (i) N2O is a powerful and very stable greenhouse gas which can be considered now as the dominant ozone-depleting substance emitted in the 21 st century in our atmosphere (Ravishankara et al, 2009). The monitoring of its chemical activity during its transport from the troposphere to the stratosphere is crucial to control the ozone depletion; (ii) N2O is actually monitored in the troposphere and in the stratosphere by probing their rovibrational IR and rotational THz transitions with sounders such as IASI (Clerbaux et al, 2009) or TALIS (Wang et al, 2020), respectively; (iii) The molecular rotational and rovibrational line parameters (line frequencies, line widths, line intensities) of N2O were measured and calculated from the mm-wave to the near-IR domains and are listed in the international spectroscopic databases such as JPL (Pickett et al 1998, THz data) or HITRAN (Gordon et al 2022, IR data). The absorption linearity was first checked in the near-IR by probing the R(17) rovibrational transition of N2O in the highly excited (3, 2, 0, 1) ← (0, 0, 0, 0) vibrational band.…”