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.

A digital-correlation full-polarized microwave radiometer is an important passive remote sensor, as it can obtain the amplitude and phase information of an electromagnetic wave at the same time. It is widely used in the measurement of sea surface wind speed and direction. Its configuration is complicated, so the error analysis of the instrument is often difficult. This paper presents a full-polarized radiometer system model that can be used to analyze various errors, which include input signal models and a full-polarized radiometer (receiver) model. The input signal models are generated by WGN (white Gaussian noise), and the full-polarized radiometer model consists of an RF front-end model and digital back-end model. The calibration matrix is obtained by solving the overdetermined equations, and the output voltage is converted into Stokes brightness temperature through the calibration matrix. Then, we use the four Stokes parameters to analyze the sensitivity, linearity, and calibration residuals, from which the simulation model is validated. Finally, two examples of error analysis, including gain imbalance and quantization error, are given through a simulation model. In general, the simulation model proposed in this paper has good accuracy and can play an important role in the error analysis and pre-development of the fully polarized radiometer.

THz Atmospheric Limb Sounder (TALIS) is a microwave radiometer designed by the National Space Science Center of the Chinese Academy of Sciences (NSSC, CAS) for measuring the vertical distribution of temperature and chemical constituents in the middle and upper atmosphere. The digital spectrometer is an important part of TALIS’ back end, which mainly realizes the function of spectral analysis. The radix 16 real-time complex fast Fourier transform (FFT) algorithm used in the digital spectrometer was obtained by improving and combining the parallel processing and complex processing of the FFT algorithm. In this study, the digital spectrometer parameter selection is systematically presented, and the effect of the digital spectrometer FFT algorithm on the TALIS system sensitivity is analyzed based on the TALIS system simulation model we established in the previous stage of this research. The results show that the actual full-band sensitivity obtained after using the FFT algorithm is consistent with the ideal full-band sensitivity of TALIS for different integration time, spectral resolutions, and quantization bits. However, the results of the comparison of the actual sub-band sensitivity after using the FFT algorithm with the ideal sub-band sensitivity show that the deterioration of the sub-band sensitivity will be caused by the FFT algorithm. The mean value of the deterioration ratio was found to be approximately 18%, and the maximum value of the deterioration ratio was approximately 33%.

Hyperspectral microwave radiometer is a new type of passive microwave remote sensor for observing middle and upper atmospheric temperature, humidity, trace gas, and other parameters such as winds. The digital spectrometer, which allows the fine sampling of the spectral lines, is the core component of the radiometer. In this article, we propose the design and implementation of a new type of wideband, real-time channelized digital spectrometer, which realizes the core base-64 real-time complex fast Fourier transform (FFT) algorithm and channelization algorithm by improving the filter bank, 128-channel parallel processing of FFT and complex number processing. The digital spectrometer has a sampling rate of 20 Gsps, a quantization bit number of 8 bits, and an input bandwidth of 10 GHz, which realizes the spectrum analysis of 4096 channels. Then, an observation test was carried out using a V-band ground-based microwave radiometer equipped with the 10-GHz spectrometer, and the atmospheric temperature profile was successfully measured from the surface to the stratosphere. The retrieval results were compared with the ERA5 reanalysis data and the L2 temperature products of the FY-3-D/MWTS-MWHS and Aura/microwave limb sounder (MLS), with a better consistency, which proved the application and potential of the new wideband digital spectrometer in the atmospheric sounding.

Real-time imaging processing for microwave interferometric radiometer (MIR) has great potential in various application fields, such as onboard data processing, onboard information fusion, and alternative visual applications. The primary challenge lies in the computational complexity of the entire processing chain, including both visibility function preprocessing and brightness temperature (TB) reconstruction. In this study, the real-time estimation of the normalized threshold level is identified as the key step for enabling real-time imaging of three-level quantized MIR systems. Three algorithms—Acklam’s algorithm (AKA), polynomial fitting algorithm (PFA), and Taylor expansion algorithm (TEA)—are proposed and evaluated. The PFA provides a favorable balance between estimation accuracy and computational efficiency. Leveraging the proposed algorithms, this paper further establishes an onboard real-time processing framework for three-level quantization MIRs, enabling real-time TB imaging and radio frequency interference (RFI) localization. A real-time imaging experiment was carried out with a 15-element, 50 GHz one-dimensional MIR system, which demonstrates real-time imaging of fast-moving vehicles on the expressway with greatly reduced computational latency (an imaging time of 570.9 μs for 159 baselines). A further flight experiment employing an L-band system verifies the feasibility of onboard RFI localization, and the proposed real-time RFI localization method shows an average angular deviation of 0.32° with respect to an offline MUSIC estimator, corresponding to 2.1% of the nominal spatial resolution.

Terahertz observations are sensitive to ice-cloud scattering but require thermodynamic context and balanced spectral sampling. This study evaluates a candidate six-band Terahertz Ice Cloud Imager (TICI) configuration for next-generation Fengyun polar-orbiting meteorological satellites. Atmospheric absorption, ice-cloud scattering, and polarization sensitivity below 1 THz are simulated with the Atmospheric Radiative Transfer Simulator. Information content is assessed using 12 Weather Research and Forecasting (WRF)-derived representative composites and 200 individual midlatitude-ocean profiles. The configuration combines water-vapor observations near 183 and 380 GHz, temperature-sensitive observations near the 424 GHz oxygen band, and window observations near 243, 664, and 874 GHz. Compared with the 11-observation Ice Cloud Imager (ICI) reference, the 21-scalar-observation TICI vector provides more temperature and water-vapor degrees of freedom for signal (DFS) under both channel-specific and uniform 1 K noise. Under uniform 1 K noise, the twelve-scene mean frozen-hydrometeor DFS is 4.117 for TICI and 4.034 for ICI; the small increase is concentrated mainly in mean-particle-mass states. Band-removal and equal-dimensional tests show complementary roles for 380, 424, and 874 GHz and indicate that the thermodynamic gain is not solely due to observation count. The conceptual antenna architecture achieves simulated main-beam efficiencies above 95%, while forward-model error, receiver implementation, and footprint co-registration remain to be assessed.