In this work, the brightness temperature (TB) transfer from the microwave calibration target (MCT) to the feeder antenna in the near-field region is investigated, which is the fundamental physical process in microwave radiometer calibration. As in this scenario, the MCT and antenna cannot be separately considered as points like in far fields, it is interesting and important to study the TB characteristics of the target in cases of feeder antennas at different positions and with different aperture sizes. Recently, as reciprocity in the near field has been established, this fundamental issue can be now investigated. The study starts at a high frequency of 89 GHz when the free-space lambda is much smaller than the unit period of MCT; then, the distributions of the local TB contribution rate are calculated to understand the possible TB transfer variation. It is found that the key factor for the TB variation is the illumination area upon the array-type MCT, and as the footprint is sufficiently large to cover several pyramid units, the TB can be stable versus relative position.

In this work, an interesting phenomenon is investigated in the scenario of calibration link in microwave radiometers, where a feeder antenna is directly harvesting the radiated brightness temperature (BT) from the microwave calibration target (MCT). As reciprocity has been established for the near-field BT transfer, it is important to investigate the performance variation of the MCT in case of different antenna illumination. In this work, it is found and analyzed that at the frequencies where lambda is near to the unit period of periodic array-shaped calibration target, the reflectivity may be notably increased in case of small aperture feeder illumination. This is a disturbing phenomenon that should be avoided for practical applications.

The Microwave Radiation Imager for Rainfall Mission (MWRI-RM) is one of the most importance payload on Fengyun3G satellite (FY-3G), the first of total two rainfall mission scheduled in China, aiming to improve the accuracy of the weather forecast. This study uses the Atmospheric Radiative Transfer Simulator (ARTS) model to simulated the MWRI-RM channel brightness temperature (Tb) to verify the impact of channel bandwidth response on simulated Tbs. To run the ARTS model, ECMWF analysis datasets are used as background input data for ARTS model, and combining the MWRI-RM L1 data to calculate the OMB mean bias for each window and sounding channel. The results show that sounding channels are more sensitive to channel bandwidth response than window channels, which should be consider when simulating Tbs.

Sea surface temperature (SST) is a vital parameter at the earth-atmosphere interface. Current method can derive an all-sky SST at resolution up to 6 km by integrating thermal infrared (TIR) and passive microwave (PMW) remote sensing. However, due to the swath gap of the polar-orbit PMW sensors, current TIR-PMW integrated SST are not spatial-seamless (i.e. all-sky available). By integrating GCOM-W1 AMSR2 and FengYun-3B MWRI observations, this paper fills the BT inside the swath gap to reconstruct a spatial-seamless PMW brightness temperature (BT) and then introduces Aqua MODIS SST to estimates a 4-km all-sky SST, the spatial resolution and coverage of which outperforms the current TIR-PMW integrated SST. Results show that the reconstructed BT highly agrees with the original BT and the estimated SST has accuracy of 0.67 K-0.72 K when validated against in-situ SST. This study would be beneficial for associated studies such as climate change on large scales.

A rainfall retrieval algorithm for tropical cyclones based on dual-polarized brightness temperature (Tb) from the Fengyun 3C (FY-3C) Microwave Radiation Imager (MWRI) radiometer is presented. Since the nonlinear relationship between rain rate and Tb, the “beamfilling effect” is corrected to make the liquid water absorption closer to the Mie absorption. The rain rate retrieval is based on the unique relationship between liquid water absorption and rain rate. To evaluate the performance of MWRI retrievals, hurricane Jose is chosen as the case study, and the Global Precipitation Measurement (GPM) Dual-frequency Precipitation Radar (DPR) rainfall product is used as a reference dataset. The MWRI retrieved rain rates show good consistency with DPR product in hurricane Jose rainfall distribution and statistical comparison, with total bias and RMS of 0.24 mm/h and 2.36 mm/h, respectively.