Zhaoguang Bai

As the successors of the overdue HuanjingJianzai-1 (HJ-1) satellites and new members in Chinese Environmental Protection and Disaster Monitoring Satellite Constellation, the first two of HuanjingJianZai-2 series satellites (HJ-2 A/B) have been launched on September 27, 2020. Each satellite carries four sensors, including the Polarized Scanning Atmospheric Corrector (PSAC), the charge-coupled device (CCD) camera, the hyperspectral imager (HSI) and the infrared spectroradiometer (IRS). Among them, PSAC is mainly used for the monitoring of atmospheric parameters to provide data support for atmospheric environmental monitoring and atmospheric correction of data from other sensors. To test the in-orbit performance of PSAC, we develop the “day-1” aerosol and water vapor retrieval algorithms. The preliminary validation results based on ground-based observations show that the aerosol optical depth (AOD) and columnar water vapor (CWV) datasets developed based on PSAC data have high accuracy and can effectively characterize the temporal trends of AOD and CWV. The accuracy of PSAC AOD dataset is better than the expected error ±(0.05 + 0.2 * AODAERONET), and the accuracy of PSAC CWV dataset is better than the expected error ±(0.5 + 0.15 * CWVAERONET). To eliminate the negative impact of the atmosphere on CCD data and expand its application range, aerosol and water vapor data developed based on PSAC are used for atmospheric correction of CCD data. Compared with L1 CCD data, the texture details and clarity of CCD data after atmospheric correction have been significantly improved.

A new land surface clustering algorithm is developed to retrieve soil moisture (SM) using the Global Navigation Satellite System reflectometry (GNSS-R) technique. Data from the BuFeng-1 (BF-1) twin satellites A/B, a pilot mission for the Chinese GNSS-R constellation, is used for SM retrieval. The core concept of the algorithm is to cluster global land areas into different types according to the land properties and calculate the SM type by type, based on the linear relationship between equivalent specular reflectivity (ESR) and SM. The global comparison between the results and SM product from the SMAP mission shows the correlation coefficient (R) is 0.82, and unbiased root mean square error (ubRMSE) is <formula><tex>$0.070 cm^3.cm^-3$</tex></formula>. The results also show good agreement compared with in situ SM measurements with the mean ubRMSE of<formula><tex>$0.036 cm^3.cm^-3$</tex></formula>. This study proves that the global SM can be retrieved successfully from the BF-1 mission with the land surface clustering algorithm. By taking full advantage of the similarity of land surface physical properties in different regions, the algorithm provides a practical approach for global SM retrieval using spaceborne GNSS-R data.

The Environment and Disaster Monitoring and Forecasting Small Satellite Constellation HJ-1A/1B satellites is the first Chinese remote sensing satellite constellation whose images may be perfectly combined in orbit.All of the performances are satisfactory in-orbit test.The paper gives an evaluation of the in-orbit performance,which is very useful for follow-on application work.

Launched on June 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> , 2019, Bufeng-1 twin satellites that carry the Chinese first generation spaceborne GNSS-R instruments started using reflected GNSS signals to perform earth observation. By utilizing the Bufeng-1 Normalized Bistatic Radar Cross Section (NBRCS), the preliminary results show that BuFeng-1 has a high agreement compared with ECMWF ERA5 or ASCAT observations in the low-to-moderate wind speed range. In this paper, the measurements of Bufeng-1 will be aligned with the hurricanes observed by Stepped Frequency Microwave Radiometer (SFMR) mounted on NOAA aircraft during 2019 Hurricane Season in a certain spatial-temporal matchup criteria. Then, a power function relationship between Bufeng-1 NBRCS and wind speeds under severe sea states is illustrated in the first time. This study is presented to discuss the limitations and issues for the future research of new version of wind speed product of Bufeng-1 mission.

In order to formulate accurate and reasonable random vibration test conditions for optical cameras and solve the problem of conservative design of test conditions caused by inaccurate simulation calculation, this paper proposes a general method for the design of random vibration specification for small satellites’ optical cameras. First, we derive the dynamic response formula, which lays a foundation for the small satellite dynamic simulation calculation. Then, the response of the optical camera mounting surface, which is obtained by the dynamic calculation of the small satellite finite element model, and the random vibration test conditions of the camera process is enveloped to obtain the preliminary random vibration test condition of the new research optical camera. Subsequently, we combine the random vibration test data of the optical remote sensing satellite, which has been used in orbit, and revise the preliminary random vibration test conditions of the new research camera in terms of response magnitude and frequency. Finally, we verify the rationality of this method through random vibration test of a small satellite. This scheme is conducive to the establishment of more reasonable and feasible random vibration test conditions for small satellites’ optical cameras, which is beneficial to the development and production of optical cameras.