The interferometric microwave radiometer (IMR) utilizes an interferometric synthetic aperture technique to achieve high spatial resolution in low-frequency microwave remote sensing, addressing the challenges of deploying large-scale passive sensors in space. IMR measures spatial harmonics of scene brightness temperature, known as visibility, which are then used in inversion algorithms to reconstruct the target brightness temperature. In 1-D IMR, the interferometric synthetic aperture technique is applied only in the cross-track direction, resulting in higher resolution compared with the coarser along-track direction determined by the real antenna aperture. Current research focuses on cross-track inversion, which has yielded promising results; however, the low along-track resolution remains a significant limitation for its overall application. This article introduces the Backus-Gilbert (BG)-inspired 1-D IMR resolution enhancement method, inspired by real aperture microwave radiometer techniques, to address along-track resolution limitation. The study utilizes the L-band 1-D IMR of the Microwave Imager Combined Active and Passive (MICAP) aboard the Chinese Ocean Salinity Satellite as an example. Results from synthetic test images and hardware-in-the-loop simulation demonstrate that the proposed method enhances along-track resolution and provides the flexibility to optimize for either higher image quality or radiometric resolution comparable to the traditional 1-D IMR inversion method. Additionally, it improves the accuracy of salinity measurements in coastal areas.

Microwave radiometers are widely used in Earth observation and ocean monitoring for their strong penetration ability. Nevertheless, their utilization is somewhat constrained by their intrinsic low-resolution capability, particularly in complex applications such as coastal zone monitoring and analysis of typhoons. To overcome this limitation, resolution enhancements are necessary. Here, we present a novel resolution enhancement technique, the alternating proximal gradient (APG) method, applied to Haiyang-2B (HY-2B) Scanning Microwave Radiometer (SMR) data. This method is based on the decorrelation approach and incorporates total variation constraint. The APG method, along with the Backus-Gilbert (BG) method, are both applied to the 6.925GHz data of HY-2B SMR. Both simulated and real HY-2B SMR data from two representative regions, including land-sea transition zones and cyclonic storms, are analyzed. Results show that both the BG method and the APG method can significantly enhance details obscured in the original SMR data. Furthermore, the enhanced brightness temperatures are compared to the AMSR-2 25 km product, revealing that the APG method provides more consistent results and contains more reliable information than the BG method in terms of resolution enhancement.

This study develops a new sea surface temperature (SST) retrieval algorithm based on statistical regression that utilizes WindSat satellite data and in situ SST quality monitor (iQuam) buoy data. The proposed algorithm introduces new rules to remove abnormal brightness temperatures (TB) due to land, sea ice, radio frequency interference (RFI), and sun glint. Besides, SST data from 2019 to 2022 are generated from the HY-2B satellite’s scanning microwave radiometer (SMR) using a two-step retrieval method. Our study reveals that wind speed (WS), cloud liquid water (LW), and wind direction have significant crosstalk effects on SST retrieval, which increases exponentially when the cloud LW exceeds 0.1 mm. The crosstalk effect can be significantly reduced by incorporating WS fitting in the SST retrieval algorithm. By fitting iQuam SST data, the multiple localizing sea surface WS and latitude algorithms are developed, significantly reducing the impact of crosstalk parameters on SST retrieval and improving the SST retrieval accuracy. Also, the algorithm performed well in correcting the nonlinear response of TB and SST. The results reveal that the retrieval algorithm eliminates bias across different WSs, water vapor (WV), and cloud LW ranges and performs consistently on ascending and descending orbits. The overall bias of the SMR four-year SST product is$-0.004\,\,^{\circ }\text{C}$, with a standard deviation (STD) of 0.588 °C, posing a substantial improvement over the existing product with a bias of$-0.022\,\,^{\circ }\text{C}$and an STD of 0.803 °C. Moreover, the four-year fluctuation of STD is very small, indicating excellent stability of the retrieval algorithm.

Long-term and stable brightness temperature (TB) measurements observed by microwave radiometers are of great significance in studying the variation in geophysical parameters and their trend analysis. A modified vicarious cold reference (MVCR) method for the scanning microwave radiometer (SMR) TBs onboard the Haiyang-2B (HY-2B) satellite is developed and used to estimate the stability of the TBs of L2A-TB and L2A-TC, which corresponds to TBs before and after intercalibration, respectively. Data from November 1, 2018, to October 31, 2021, are used for the stability assessment. The results show that there are several channels in L2A-TB with annual drifts of TBs greater than 0.1 K per year (K/year), while the TBs of L2A-TC after intercalibration are quite stable, with annual drifts that are all less than 0.1 K/year. In conclusion, the SMR TBs after intercalibration achieve better stability. The robustness of the MVCR method is demonstrated using simulated SMR TBs. After removing the annual harmonics, the coldest TB sequence is more stable, and a more realistic annual drift can be obtained.

The Chinese Ocean Salinity Satellite is part of the Chinese ocean dynamic satellite series, and is dedicated to global SSS observation with two payloads onboard. These two payloads, named the Interferometric Microwave Radiometer (IMR) and the Microwave Imager Combined Active and Passive (MICAP), both adopt interferometric aperture synthesis technology. IMR is a two-dimensional L-band interferometric radiometer system with a Y -shaped antenna array. MICAP is a one-dimensional passive/active combined system, where the L-, C-, and K-band interferometric radiometers' antenna arrays are arranged in a line, and the active device is an L-band scatterometer. Based on the payload configurations, an end-to-end simulation shows that, with the assistance of the C- and K-band radiometers and the L- band scatterometer, the combined retrieval accuracy improves compared with the SSS retrieved using only L-band TB and auxiliary parameters. The best accuracy of SSS is achieved when considering all the available measurements from two payloads together in a combined retrieval.

Haiyang-2B (HY-2B) is the second marine dynamic environment satellite of China. It carries several payloads, which includes a scanning microwave radiometer (SMR). Sea surface temperature (SST) is one of the main products of SMR. This study compares SST derived from SMR to in-situ SSTs in all of 2020. The collocations of HY-2B SRM and insitu SSTs were generated with the spatial window of 25km and the temporal window of 30 min, and the matchup data set includes 2696012 points from all over the global sea surface areas. Results show that SMR SST has a mean bias of 0.068°C (SMR minus buoy) and root-mean-square error (RMSE) of 0.851 °C in the global ocean area. By analyzing the global bias distribution map, we can conclude that the larger SST bias points mainly concentrated along the coast, sea ice, and high wind speeds areas where deteriorated the global overall accuracy performance. To prove it, three different areas were selected and analyzed separately. The results show that the RMSE in open ocean over mid and low latitudes is 0.66°C, while RMSEs in the nearshore zone and high wind speeds areas are 0.8°C and 1.1 °C, respectively.

China's ocean dynamic monitoring satellite Haiyang-2B (HY-2B) has been in orbit for more than one year. Payload named scanning microwave radiometer (SMR) with five frequency channels onboard the HY-2B is an instrument mainly used to monitor and study ocean environment and to obtain ocean dynamic parameters like sea surface wind, temperature, etc. One issue is that high wind speeds in typhoons cannot be monitored by brightness temperature (TB) data at high frequency channels due to heavy rain, while the low frequency channel TB are capable of high wind speed retrieval but are limited to the low spatial resolution. This paper intends to enhance SMR's spatial resolution in low frequency channels by applying the interpolation method developed by Backus and Gilbert. Preliminary results indicate that TB data after spatial resolution enhancement show more details of typhoon structures and will provide more information for the high wind speed retrieval.

China's Haiyang-2B satellite (HY-2B) has been in orbit for over a year, since it was launched on October 25th, 2018. HY-2B is equipped with both active and passive microwave remote sensors. Payload named scanning microwave radiometer (SMR) with five frequency channels in HY-2B is an instrument mainly used to monitor and investigate ocean environment and obtain ocean dynamic parameters like sea surface temperature, surface wind speed, atmospheric water vapor and cloud liquid water, etc. This paper introduce a method to optimize the masks of land and sea ice based on HY-2B SMR in order to improve the inversion accuracy of sea surface temperature. The idea of the method is subdividing the 3dB footprint into more sophisticated points, and every point is geolocated and marked as Land, Sea water or Sea ice. Finally, the subdivided mask is used for SST inversion and compared with the WINDSAT SST inversion results of the Coriolis satellite. The chosen of the method's parameters will compromise between numbers available for inversion and inversion accuracy.

As the Hai-Yang 2B (HY-2B) satellite was launched on 25 October 2018, the brightness temperature measured by the scanning microwave radiometer (SMR) on the HY-2B Satellite are analyzed including the commissioning phase. In order to evaluate the brightness temperature situation, comparisons between SMR and GMI brightness temperature from 6 to 37GHz over the ocean are preliminary implementation, and the results are encouraging.

The algorithm of inversing the SST from the SMR onboard on HY-2B satellite is an empirical regression method based on the physical model to calculate the empirical relationship between the brightness temperature and the different physical parameters of the ocean and atmosphere. In order to test the preliminary result of SST retrieved from HY-2B satellite SMR, the SST is validated according to the IQUAM in-situ SST and the space-borne WindSat SST. The performance of the instrument is still being estimated and SST retrieval algorithm is still improving.