DESIGN AND VERIFICATION OF MICROWAVE HYPERSPECTRAL ATMOSPHERIC SOUNDER ON THE CHINESE NEW GENERATION METEOROLOGICAL SATELLITE

J. He¹

¹Key Laboratory of Microwave Remote Sensing, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China, Email address hejieying@mirslab.cn

Introduction

Atmospheric temperature and humidity are key elements in global weather forecasting and climate change research. They are two important parameters describing the thermodynamic state of the atmosphere, which directly affect the interaction between solar shortwave radiation and longwave radiation from the Earth-atmosphere system, thereby influencing the balance of global radiant energy budget.

Current numerical weather prediction systems have put forward higher requirements for the detection accuracy and vertical resolution of atmospheric temperature and humidity profiles. Therefore, it is necessary to explore new technical means to enhance the detection capability of atmospheric temperature and humidity profiles.

Description of Microwave hyperspectral Instrument

The Microwave Hyperspectral Sounder of FY-5 is an upgraded replacement for the microwave humidity sounder and microwave temperature sounder of FY-3. It adopts an integrated design based on the mature existing microwave temperature sounders and microwave humidity sounders.Channel densification design is implemented in the 183GHz detection frequency band, and 229GHz detection channels are added. Meanwhile, fine spectrum detection technology is applied in the 50-60GHz and 22-32GHz detection frequency bands. This technology is mainly characterized by refined spectral sampling within the frequency bands, enabling the reception of nearly one hundred or more narrowband spectral channels and the near-continuous sampling of atmospheric radiation signals in the microwave frequency bands.Since particles such as ice, clouds, rain, and snow in the atmosphere exert a certain attenuation effect on microwave radiation from the Earth’s surface, different atmospheric information can be obtained from different channels. Through calibration and inversion, an accurate description of the Earth’s atmosphere can be derived.

There are 8 detection frequency bands in total, ranging from 22 to 229 GHz, specifically: 22-32 GHz, 50-60 GHz, 89 GHz, 118 GHz, 166 GHz, 183 GHz, and 229 GHz. These bands cover all the detection frequencies of MWTS (Microwave Temperature Sounder), MWHS (Microwave Humidity Sounder), and MWS (Microwave Sounder). On the basis of the existing temperature sounders and humidity sounders of the Fengyun-3 series, channel densification has been implemented. Additionally, the two absorption bands (22-32 GHz and 50-60 GHz) are equipped with both digital fine-spectrum channels and analog channels, achieving simultaneous coverage of the two types of channels. The digital channels adopt a standard modular design for flexible configuration, and the number of digital channels and their bandwidth can be programmed on-orbit. For polarization settings, the co-polarization mode for both dual-oxygen and dual-water vapor channels is adopted. Simulation and verification have shown that the combination of dual-oxygen and dual-water vapor channels significantly improves the inversion accuracy.

Two sets of high-speed digital spectrometers (operating at 23.8/31.4 GHz and 50-60 GHz) are added to enable fine spectrum detection. Flexible implementation of different bandwidth subdivision schemes is achieved through software programming, with a maximum spectral resolution of up to 3 MHz. Parameters such as the number of channels, bandwidth, and frequency range can be flexibly adjusted according to actual temperature and humidity inversion requirements. By configuring the number of channels for sudden weather phenomena, the capability to monitor and early warn of severe weather can be further enhanced.The proposal of the variable channel bandwidth configuration strategy is intended to overcome the limitations caused by fixed bandwidths. This strategy optimizes channel bandwidth configurations for different frequency bands and absorption lines to maximize inversion accuracy and vertical resolution.

Research results show that different frequency bands require specific bandwidth configurations to adapt to different observation targets. In the 60 GHz frequency band, using a 3 MHz bandwidth can achieve better performance in indicators such as effective detection height and full width at half maximum (FWHM). The configuration of spectral bandwidth has become one of the key factors affecting inversion performance. Traditional microwave fine-spectrum radiometers use fixed bandwidths to cover different frequency bands, but this fixed-bandwidth scheme may not provide the optimal inversion effect under all atmospheric conditions. Therefore, how to flexibly adjust bandwidth configurations to adapt to different atmospheric conditions has become an important direction for improving inversion accuracy.

Campaigns and retrievals

The finally constructed channel configuration scheme was systematically compared across indicators such as measurement response, FWHM (Full Width at Half Maximum), posterior error improvement rate, and inversion RMSE (Root Mean Square Error). The results show that the optimized fine-spectrum configuration achieves optimal performance across multiple performance dimensions: the RMSE of temperature inversion can be as low as 1.2 K, the RMSE of humidity inversion is reduced to 2.5 × 10⁻³ kg/kg, the improvement in posterior error is over 10% higher than that of ATMS (Advanced Technology Microwave Sounder), and the scheme demonstrates significant ability to resolve the layered structure of the boundary layer. Specifically, the FWHM of temperature is reduced by approximately 1 km, and the FWHM of humidity is reduced by approximately 500 m.

Conclusions

The FY-5 microwave fine-spectrum observation instrument was developed as a quantitative upgrade solution to meet the operational needs of the next-generation polar-orbiting meteorological satellites, based on the FY-3 microwave humidity and temperature instruments. Simultaneously, technical index feasibility analysis and validation were conducted for the upgrade scheme. Through field trials and retrieval analyses, it has been demonstrated that the innovative fine-spectrum observation approach can enhance observational capabilities, providing sufficient technical support for the establishment of the next-generation meteorological satellite program.