THz Atmospheric Limb Sounder (TALIS) is a microwave limb sounder being developed for atmospheric vertically resolved profile observations by the National Space Science Center, Chinese Academy of Sciences (NSSC, CAS). It is designed to measure temperature and chemical species such as O₃, HCl, ClO, N₂O, NO, NO₂, HOCl, H₂O, HNO₃, HCN, CO, SO₂, BrO, HO₂, H₂CO, CH₃Cl, CH₃OH, and CH₃CN with a high vertical resolution from about 10 to 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 and to compare them with that of Aura MLS standard spectrometers. Single scan measurement and averaged measurement are considered in the simulation, respectively. The temperature profile can be obtained with a precision of <2 K for a single scan from 10 to 60 km by using the 118 GHz radiometer, and the 240 and 643 GHz radiometers can provide temperature information in the upper troposphere. Chemical species such as H₂O, O₃, and HCl show a relatively good single scan retrieval precision of <20 % over most of the useful range and ClO, N₂O, and HNO₃ can be retrieved with a precision of <50 %. The other species should be retrieved by using averaged measurements because of the weak intensity and/or low abundance.

The THz atmospheric limb sounder (TALIS) is a microwave radiometer designed by the National Space Science Center, Chinese Academy of Sciences (NSSC, CAS), to sound the vertical distribution of the atmosphere. It mainly consists of the antenna and feed system, the radio frequency (RF) front-end receiver and intermediate-frequency (IF) modules, and the digital back-end spectrometer. The TALIS is used to measure the temperature and chemical composition of the Earth’s atmosphere at a range of 0–100 km with good vertical resolution. The offset paraboloidal antenna of the TALIS is composed of a single projected 1.6-m aperture reflector combined with four independent feeds at four frequencies. The receiver of the TALIS consists of four superheterodyne radiometers operating at room temperature with center frequencies of 118, 190, 240, and 640 GHz. The back-end spectrometer of the TALIS includes four fast Fourier transform spectrometers (FFTSs), each with an analysis bandwidth of 2 GHz and a spectral resolution of 2.3 MHz. In this study, preliminary performance analysis of the TALIS system was performed based on the power spectrum of cold and hot targets, a calibration method was proposed for the spectral lines, and sub-band sensitivity results were obtained. The results showed that for the four frequency band radiometers, the mean sub-band sensitivities were lower than 5.7 K and the standard deviations were lower than 0.8 K, which will have a positive impact on future retrieval applications.

Microwave humidity and temperature sounder (MWHTS) is an important payload of FENGYUN-3D (FY-3D) satellite. MWHTS is designed as total power radiometer because of its high radiometric resolution (NEDT) and simple configuration. NEDT is one of the most important indicators for MWHTS. However, the traditional NEDT analysis results have a large error compared with the measured results. To estimate the overall radiometer performance, this paper presents a numerical system simulation model that can be used to estimate NEDT. The model considers two of three main components that degrade the NEDT: thermal noise and calibration error. The third components 1/f noise is calculated by analyzing the power spectrum of the actual output voltage. Based on digital signal processing, this paper presents a method for accurate system modeling, including radiation source modeling, frontend modeling and backend modeling. The simulation model is validated by comparing the dynamic range, linearity and standard deviation of output signals of simulation system and actual instrument. In this paper, the model has been applied to NEDT estimate of 15 MWHTS channels operating from 89 GHz to 183 GHz. The comparison of estimate results between simulation model and actual instrument shows they are in good agreement and the maximum error is no more than 18%.

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.

The ice water path (IWP) is an important cloud parameter in atmospheric radiation, and there are still great difficulties in its retrieval. Artificial neural networks have become a popular method in atmospheric remote sensing in recent years. This study presents a global IWP retrieval based on deep neural networks using the measurements from the Microwave Humidity Sounder (MWHS) aboard the FengYun-3B (FY-3B) satellite. Since FY-3B/MWHS has quasi-polarization channels at 150 GHz, the effect of the polarimetric radiance difference (PD) was also studied. A retrieval database was established using collocations between MWHS and CloudSat 2C-ICE (CloudSat and CALIPSO Ice Cloud Property Product). Then, two types of networks were trained for cloud scene filtering and IWP retrieval. For the cloud filtering network, the microwave channels show a capacity with a false alarm ratio (FAR) of 0.31 and a probability of detection (POD) of 0.61. For the IWP retrieval network, different combination inputs of auxiliaries and channels were compared. The results show that the five MWHS channels combined with scan angle, latitude, and the ocean/land mask of inputs of auxiliary variables perform best. Applying the cloud filtering network and IWP retrieval network, the final root mean squared error (RMSE) is 916.76 g m⁻², the mean absolute percentage error (MAPE) is 92 %, and the correlation coefficient (CC) is 0.65. Then, a tropical cyclone case measured simultaneously by MWHS and CloudSat was chosen to test the performance of the networks, and the result shows a good correlation (0.73) with 2C-ICE. Finally, the global annual mean IWP of MWHS is very close to that of 2C-ICE, and the 150 GHz channels give a significant improvement in the midlatitudes compared to using only 183 GHz channels.

The vertical profiles, spatiotemporal distribution and trends of temperature and humidity in the middle atmosphere are significant for numerical weather prediction and the analysis of global climate change. To better design and apply spaceborne microwave spectrometer on the new generation Fengyun satellite, the sensitivities of the spectrometers at 22.235, 50-60, 118.75, 183.31, 325.153, 380.33, 424.77, 448.0 and 556.94 GHz are analyzed, respectively. Qpack2 included in the atmospheric radiative transfer simulator (ARTS) is used. The results show that the retrieval accuracy of the 50.0-60.0 GHz spectrometer is obviously better than other spectrometers, and the effective detection height (EDH) is the highest, reaching 0.233 hPa. The humidity profiles bigger than 500 hPa are well detected by the seven channels of the Humidity and Temperature Profiler (HATPRO) or 22.0-32.0 GHz spectrometer. The retrieval accuracy is better than 6%, which greatly improves the retrieval performance of humidity profiles in the lower troposphere over the sea. In addition, this frequency band is not affected by errors in sea surface temperature or wind speed. The humidity profiles over the sea and land in the middle atmosphere under clear-sky and cloudy-sky conditions are well detected by the 183.31 and 556.94 GHz spectrometer. The EDH can be increased to 1.14 hPa by the 556.94 GHz spectrometer. In the design and application of future spaceborne microwave spectrometers for temperature and humidity profiles detection, the spectrometers mentioned above are good candidates, and the parameter configuration of these spectrometers can be used as a reference.