Since the first microwave humidity sounder (MWHS) launched on May 27, 2008, six MWHSs deployed on polar-orbiting FengYun-3 (FY-3) satellites to date have been continuously providing temperature and humidity information for over 15 years. Compared to the predecessors MWHS onboard FY-3A/B/C/D, the central frequency of the window channel is shifted from 150 to 166 GHz for MWHS-II onboard FY-3E/F, and the additional low noise amplifier (LNA) embedded in the radio frequency (RF) module optimizes the performance of the receiver system, leading to a significant reduction in the noise temperature of the receivers. The reduced bias and standard deviation of simultaneous Nadir overpass (SNO) results between MWHS-II and Advanced Technology Microwave Sounder (ATMS) further corroborate that that the instrument performance has been improved and updated. The interchannel interference of FY-3E/F is mitigated, and the channel sensitivities are also enhanced according to the postlaunch test results.

FengYun-3F (FY-3F) is a sun-synchronous satellite launched on August 3, 2023. It crosses the equator at a local time of 10:15 a.m. and will be a substitute for FY-3C. This study introduces the preflight and in-orbit calibration of microwave humidity sounder-II (MWHS-II) onboard FY-3F. The instrument nonlinearity and radiometric sensitivity are characterized in the ground thermal vacuum chamber (TVAC) tests. The residual of nonlinearity correction is within 0.5 K, depending on viewing scenes and channels. As a substitute for its predecessor FY-3C, the performance of MWHS-II onboard FY-3F is compliant with requirements. The in-orbit radiometric sensitivity of the sensor is consistent with the prediction of the TVAC test results, with margins of 20%–60% relative to the requirements. The in-orbit behavior of the sensor is further evaluated by simultaneous nadir overpass (SNO) with the advanced technology microwave sounder (ATMS) and the difference between observation-background (O-B). The results confirm that the radiometric performance of MWHS-II onboard FY-3F is improved, compared to FY-3C. With stable and consistent observations, MWHS-II onboard FY-3F will benefit numerical weather predictions by providing accurate temperature and humidity information at the 118- and 183-GHz bands.

On November 15, 2017, the fourth satellite, Feng Yun-3D (FY-3D), of the new generation of Chinese polar orbit meteorological satellites was successfully launched into orbit. As one of the key payloads, the second-generation Microwave Humidity Sounder (MWHS II) has 15 channels for observing atmospheric temperature and moisture. In the ground data processing system, the calibration is completed for every scanning period, and then, brightness temperature (TB) data are obtained with calibration coefficients. In order to analyze the performance of MWHS II, one year of in-orbit data are used to monitor the trend of internal blackbody target temperature, instrument temperature, calibration counts, and automatic gain control (AGC), and the results indicate whether the instrument is working well. The instrument noise equivalent differential temperature (NEDT) is calculated, and the value satisfies the design requirements. Two methods are used to validate FY-3D MWHS II measurements. One is the simultaneous nadir overpass (SNO) approach: in this method, ATMS is chosen as the reference sensor, and the standard deviations for five humidity sounding channels are all less than 1.3 K. In the alternate approach, a comparison of the observed and simulated TB of MWHS II is carried out between FY-3C and FY-3D. The results also demonstrate a consistent performance between the two instruments.

This paper focuses on precipitation detection using microwave humidity temperature sounder (MWHS-II) onboard FY-3C satellite. Some of its channels are sensitive to moisture at different atmospheric altitudes and provide vertical precipitation information. In this paper, precipitation detection algorithm over ocean using scatter index (SI) and over land using direct classification are proposed, then rain rate retrieval algorithm is completed on the basis of the precipitation detection algorithm. For ocean, compared with the Level 2 precipitation detection data product of FY3C MWHS-II, the correctness of the ocean precipitation detection algorithm is close to 100% (| latitude |50°), and compared with TMPA 3B42 data product, it can reach 96.5%. For land, compared with the TMPA 3B42 data product, its accuracy is higher than 93%. It can be seen that the proposed algorithm for detecting precipitation for ocean and land is effective.

This paper focuses on rainfall retrievals using 118GHz and 183GHz channels of microwave humidity temperature sounder (MWHS-II), which has been launched onboard FY-3C satellite. These channels contain various information about the rain. The dataset of FY-3C and GPM are matched in the aspects of time and location and the retrieval algorithm is established. Using the 118GHz and 183GHz channels, the correlation coefficients of retrieval for the ocean and land are 0.8044 and 0.7001 respectively. However, the correlation coefficients are 0.6473 and 0.5438 respectively without using the 118GHz channels, and the result are 0.7284 and 0.5611 respectively without using the 183GHz channels. Comparing the result, we analyze the sensitivity of the 118GHz and 183GHz using the Community Radiative Transfer Model (CRTM).

The Microwave Humidity Sounder (MWHS) is a five-channel microwave radiometer in the range of 150-191 GHz onboard FengYun 3 (FY-3). Before the launch of FY-3A, the intensive thermal vacuum (TVAC) tests for MWHS had been carried out in a 2-m TVAC chamber, and the basic parameters such as receiver nonlinearity were obtained. Four-year operation shows that the performance of FY-3A MWHS remains stabile. The variations among space views and warm target views in the interval of scan lines were generally within 20 counts. In addition, the temperature fluctuation of the warm target in a single pass is within 0.5 K. Primarily, due to the nonlinearity correction obtained from the TVAC test, radiance measurements of MWHS agree well with NOAA-17 AMSU-B and NOAA-18 Microwave Humidity Sounder (MHS) data. Averaged brightness temperature differences between FY-3 MWHS and NOAA-17 AMSU-B, at simultaneous cross-overpass points, are less than 1.08 K for the channels at 183 ± 1 GHz. In the observation-minus-background comparison, the observed and simulated brightness temperature biases of FY-3 MWHS and NOAA-18 MHS exhibit similar performance in the 183.31 ± 1 GHz channel; but in the 183.31 ± 7 GHz channel, MWHS agrees better with background. It is anticipated that FY-3 MWHS data will contribute to numerical weather prediction.

The payload on board the FengYun 3 (FY-3) satellite series has been providing critical observations to the Earth, and the observation data have been processed and distributed to various users by the corresponding ground application system. In this paper, the FY-3 payload and its future development plan are presented, and its ground system is introduced. The major characteristics of the FY-3 instruments and the requirement on the instruments for major applications are discussed as well. There are nine new instruments, including the Microwave Temperature Sounder (MWTS), Microwave Humidity Sounder (MWHS), Infrared Atmospheric Sounder (IRAS), Medium-Resolution Spectral Imager (MERSI), Microwave Radiation Imager (MWRI), Solar Backscatter Ultraviolet Sounder, Total Ozone Unit, Solar Irradiation Monitor, and Earth Radiation Measurement. The data quality from the IRAS, MWTS, MWHS, and MWRI has proved to be good, and according to our evaluation at the European Centre for Medium-Range Weather Forecasts (ECMWF), the data have a very high availability. The MERSI has 20 visible (VIS) and infrared (IR) channels, of which three are VIS channels with a 250-m spatial resolution, one is a near-IR channel with a 250-m spatial resolution, and one is a long-wave IR channel with a 250-m spatial resolution. The global data at a 250-m spatial resolution are very useful in weather, disaster, and environmental monitoring. Compared with the ground observations, the ozone products derived from the FY-3 series are highly accurate. We have completed the calibration and validation of these sensors and most products.

The Microwave Radiation Imager (MWRI) on board the FengYun-3A/B satellites observes the Earth atmosphere at 10.65, 18.7, 23.8, 36.5, and 89.0 GHz with each having dual polarization. Its calibration system is uniquely designed with a main reflector viewing both cold and hot calibration targets. Two quasi-optical reflectors are used to reflect the radiation from the hot load and cold space to the main reflector. In the MWRI calibration process, a radiation loss in the beam transmission path must be taken into account. The loss factor in the hot load transmission path is derived using the antenna pattern data measured on ground and satellite data observing over the Amazon forest where the scene temperature is steady and close to the hot load. The instrument nonlinearity factors at different channels are also evaluated over a wide range of brightness temperatures and compared with the results from the ground vacuum test. After a cross-calibration with Windsat data, atmospheric products are derived from MWRI brightness temperatures with the accuracy similar to those from the legacy sensors (e.g., the Special Sensor Microwave/Imager).

During recent decades, China has successfully launched several programs of satellite-borne remote sensing, including the meteorological Feng-Yun (FY, “wind cloud”) series and oceanic Hai-Yang (HY, “ocean”) series, in broad spectra, i.e., optical, infrared, and microwave. Since the initiation from the early 1970s, a total of nine meteorological satellites, FY series, including five polar-orbit satellites and four geostationary satellites, have been successfully launched. Chinese FY has become an important component of global meteorological satellites systems and continues to maintain long-term stable operations of both polar and stationary meteorological satellites. Later in 2002, China's HY-1, an oceanic color satellite, was launched and is now in good operation. The successive HY-2 and HY-3 of the HY series, including microwave sensors, are also on schedule. Relevant basic research, application, and operational service of satellite-borne remote sensing and Earth observation have been well implemented. In this paper, a brief overview of Chinese satellite-borne remote sensing, FY and HY series, is presented, and some progress is introduced.