## 6 Conclusions  
In this paper, a method to estimate TC intensity was developed, using SSMIS radiometer and HY-2A scatterometer data from the Northwest Pacific, from 2012 to 2017. First, we studied the correlation between the TB parameters, SSW parameters, and the MSW, to form the best-track data of the TCs. We found, for the SSMIS radiometer, that (1) the parameters of 19 GHz and 37 GHz channels give higher correlations with the TC MSW; (2) the horizontal polarization has a higher correlation  
Figure 12: Scatter plot of the comparison between the estimated maximum wind speed and the National Hurricane Center (NHC) best-track data and aircraft reconnaissance data in the Atlantic basin, and the Northeast and North Central Pacific basin. The solid line is the fitting line. (**a**) Proposed model vs best-track data (**b**) proposed model vs aircraft observations.  
than the vertical polarization at the same frequency; (3) the most well-correlated parameter for all frequencies is MIN; (4) the parameters in the surrounding regions (0.75-1.25\({}^{\circ}\) away from the TC center, especially 1\({}^{\circ}\)) tend to give higher correlations with the TC intensity. The highest correlation coefficient is 0.84, and the highest RMSE is 6.67 m/s. In addition, for HY-2A scatterometer, (1) the most well-correlated parameter for all radii is MEAN (and a few MIN); (2) the parameters for the surrounding regions (0.75-1.5\({}^{\circ}\) away from the TC center) tend to give higher correlations with the CMA best-track data. The highest correlation coefficient is 0.83, and the highest RMSE is 7.09 m/s.  
Then, the TC intensity-estimated model was developed based on multiple linear regression, using selected parameters. We evaluated our estimated method by using independent verification data. The R\({}^{2}\) of our verification is 0.83, the RMSE is 5.94 m/s, the MAE is 4.62 m/s, and the BIAS is \(-0.43\) m/s. The estimated results of our model are therefore comparable to those of other algorithms.  
On 25 October 2018, the HY-2B satellite was launched, as well as a subsequent series of HY-2 satellites, which formed an ocean dynamics satellite constellation to provide additional TC observation data. In the next five years, the Chinese HY-2C and FY-3E, which also carry radiometer and scatterometer equipment, will be launched. There will be more satellite data for both typhoons and hurricanes available to improve and implement the proposed method at that time.  
All authors have made great contributions to this article. Conceptualization, X.Y.; Formal analysis, K.X.; Methodology, X.Y., K.X.; Software, K.X., S.W.; Validation, K.X.; Writing--original draft, K.X., X.Y.; Writing--review & editing, K.X., X.Y.  
This research was supported by the National Key R&D Program of China under Grant 2017 YFB0502800, and in part, by the National Natural Science Foundation of China under Grant 41871268, and in part, by the Key Research and Development Program of Hainan Province under Grant ZDYF2017167.  
The HY-2A microwave scatterometer data are provided by the National Satellite Ocean Application Service (NSOAS). The SSMIS microwave radiometer data are produced by Remote Sensing Systems, with support from NASA. Data are available at www.remss.com. The best-track data were obtained through the China Meteorological Administration (CMA). We are grateful to NSOAS, NOAA, and CMA for access to these data.  
The authors declare no conflicts of interest.