Microwave Humidity And Temperature Sounder Research Articles

Optimal Channel Selection of Spaceborne Microwave Radiometer for Surface Pressure Retrieval over Oceans

Abstract The O2-band channel configuration of existing microwave radiometers is not optimal for surface pressure retrieval, which limits the surface pressure retrieval accuracy. In this study, we present the results of theoretically what might be the optimal microwave channels for surface pressure retrieval. An improved iterative selection method is used to select the channels that contain the highest cumulative content of surface pressure information. The selected optimal channel set comprises 16 channels, among which 10 channels are centered at the 50–60 GHz oxygen absorption band and 6 channels are centered around the 118.75 GHz oxygen absorption line. Two representative spaceborne microwave radiometers are used for comparisons, the Advanced Technology Microwave Sounder (ATMS) on board the Suomi National Polar-Orbiting Partnership (SNPP) satellite and the Microwave Humidity and Temperature Sounder (MWHTS) on board the Chinese Fengyun-3C (FY-3C) satellite. The results of information content analysis show that the optimal channel set contains more surface pressure information than that of the combination of SNPP/ATMS and FY-3C/MWHTS (SNPP/ATMS+FY-3C/MWHTS) channels. A representative dataset from the ERA5 data is input into the plane-parallel Microwave Radiative Transfer model to obtain the simulated brightness temperature observations of the selected optimal channels and the SNPP/ATMS+FY-3C/MWHTS channels. Using the simulated observations, retrieval experiments are performed. Experimental results show that retrieval accuracies of the optimal channel set are 1.09 and 1.64 hPa for clear-sky and cloudy conditions, respectively. The retrieval accuracies are 0.60 and 0.65 hPa better than that of the SNPP/ATMS+FY-3C/MWHTS channels for clear-sky and cloudy conditions, respectively.

Comparative Study of the 60 GHz and 118 GHz Oxygen Absorption Bands for Sounding Sea Surface Barometric Pressure

The 60 GHz and 118 GHz oxygen absorption bands are prominent in the passive microwave remote sensing of atmospheric temperature, and also can be used for sounding sea surface barometric pressure (SSP). Microwave Temperature Sounder II (MWTS-II) has 13 channels in the 60 GHz band, and Microwave Humidity and Temperature Sounder (MWHTS) has 8 channels in the 118 GHz band. They are both carried on Fengyun-3C Satellite (FY-3C) and Fengyun-3D Satellite (FY-3D), which provide measurements for comparing the retrieval accuracies of SSP using 60 GHz and 118 GHz bands. In this study, based on the weighting functions for MWHTS and MWTS-II, the 60 GHz and 118 GHz channel combinations representing 60 GHz and 118 GHz are established, respectively, and the retrieval accuracies of SSP from these two channel combinations are compared in different weather conditions. The experimental results show that the retrieval accuracy of SSP at 60 GHz is higher than that of 118 GHz in clear, cloudy, and rainy sky conditions. In addition, the retrieval experiments of SSP from MWTS-II and MWHTS are also carried out, and the experimental results show that the retrieval accuracy of SSP from MWTS-II is higher. The comparative study of the 60 GHz and 118 GHz for sounding SSP can provide support for the theoretical study of microwave remote sensing of SSP with practical measurements, and further contribute to understand the performance of 60 GHz and 118 GHz in atmospheric sounding.

Precipitation Retrieval from Fengyun-3D Microwave Humidity and Temperature Sounder Data Using Machine Learning

As an important component of the Earth system, precipitation plays a vital role in regional and global water cycles. Based on Microwave Humidity and Temperature Sounder (MWHTS) onboard FY-3D satellite, four machine learning models, random forest regression (RFR), support vector machine (SVM), multilayer perceptron (MLP), and gradient boosting regression tree (GBRT), are implemented to retrieve precipitation rate, and verified with Integrated Multi-satellite Retrievals for GPM (IMERG). This paper determines the optimal hyperparameters of the machine models and proposes three linear combinations of MWHTS channels (183.31 ± 1.0–183.31 ± 3.0 GHz, 183.31 ± 1.0–183.31 ± 7.0 GHz, and 183.31 ± 3.0–183.31 ± 7.0 GHz), which can better characterize precipitation of different intensities. With the inclusion of three linear combinations, the performances of all four machine learning models are significantly improved. It is concluded that the RFR and GBRT have the best retrieval accuracy. Over ocean, the MSE, MAE, and R2 values of precipitation estimates using RFR are 1.75 mm/h, 0.44 mm/h, and 0.80, respectively, and are 1.80 mm/h, 0.45 mm/h, and 0.78 for GBRT. Simultaneously, this paper analyzes the retrieval results from the perspective of the different rain rates and temporal matching difference between MWHTS and IMERG data. The RFR and GBRT also maintain the best retrieval accuracy under the condition of Gaussian noise, indicating the relatively strong robustness and antinoise performance of ensemble learning models for precipitation retrieval.

Fusion Retrieval of Sea Surface Barometric Pressure from the Microwave Humidity and Temperature Sounder and Microwave Temperature Sounder-II Onboard the Fengyun-3 Satellite

Both the Microwave Humidity and Temperature Sounder (MWHTS) and the Microwave Temperature Sounder-II (MWTS-II) operate on the Fengyun-3 (FY-3) satellite platform, which provides an opportunity to retrieve the sea surface barometric pressure (SSP) with high accuracy by fusing the observations from the 60 GHz, 118.75 GHz, and 183.31 GHz channels. The theory of retrieving SSP using passive microwave observations is analyzed, and the sensitivity test experiments of MWHTS and MWTS-II to SSP as well as the test experiments of the contributions of MWHTS and MWTS-II to SSP retrieval are carried out. The theoretical channel combination is established based on the theoretical analysis, and the SSP retrieval experiment is carried out based on the Deep Neural Network (DNN) for the theoretical channel combination. The experimental results show that the retrieval accuracy of SSP using the theoretical channel combination is higher than that of MWHTS or MWTS-II. In addition, based on the test results of the contributions of MWHTS and MWTS-II to the retrieval SSP, the optimal theoretical channel combination can be built, and can further improve the retrieval accuracy of SSP from the theoretical channel combination.

Precipitation distribution and forecasting in hurricane ‘Hermine’

Retrievals and forecasting of precipitation based on FY-3C microwave humidity and temperature sounder (MWHTS) are carried out to validate the possibility of microwave sounder in meteorological applications. Different from current research, a novel idea combining radiative transfer theory and historical statistical method is presented. Hurricane Hermine (the first hurricane to make landfall along the apalachee bay coast Since 1966) as a study case is chose to analyse the precipitation distribution and give forecasting results in 72 hours.

Research on the selection method of FY-3D/MWHTS clear sky observation data based on neural network

The selection of clear sky data in space-borne remote sensing data is very important for its data application. For FY-3D satellite microwave humidity and temperature sounder (MWHTS), an inversion system of atmospheric cloud water content by MWHTS is established based on neural network. The cloud water content inversion value is used to select clear sky data from MWHTS observation data. The experimental results show that FY-3D/MWHTS clear sky data selection method based on neural network can effectively select MWHTS observation data, thus improving the simulation brightness temperatures accuracy of MWHTS by radiative transfer model. This method can be used to select clear sky data by using space-borne observation data itself. It is easy to operate and has important practical value for climate change research, numerical weather forecast, etc., based on space-borne observation data.

Simulating Radiometric Resolution of Microwave Humidity and Temperature Sounder Onboard the FY-3D Satellite

Microwave humidity and temperature sounder (MWHTS) is an important payload of FENGYUN-3D (FY-3D) satellite. MWHTS is designed as a total power radiometer because of its high radiometric resolution (NEDT) and simple configuration. NEDT is one of the most important indicators for MWHTS. However, the traditional NEDT analysis results have a large error compared with the measured results. To estimate the overall radiometer performance, this article presents a numerical system simulation model that can be used to estimate NEDT. The model considers two of three main components that degrade the NEDT: thermal noise and calibration error. The third component $1/f$ noise is calculated by analyzing the power spectrum of the actual output voltage. Based on digital signal processing, this article presents a method for accurate system modeling, including radiation source modeling, frontend modeling, and backend modeling. The simulation model is validated by comparing the dynamic range, linearity, and standard deviation in output signals of the simulation system and actual instrument. In this article, the model has been applied to NEDT estimate of 15 MWHTS channels operating from 89 to 183 GHz. The comparison of the estimate results between the simulation model and actual instrument shows they are in good agreement and the maximum error is no more than 18%.

Tropical Cyclone Surface Pressure Field Estimation Using Satellite Passive Microwave Observations over the Oceans

AbstractThe real time and accurate estimation of tropical cyclone (TC) surface pressure fields is highly desired in TC forecasting and analysis. Using satellite passive microwave observations over the oceans, the retrieval of TC surface pressure fields was investigated in this study, and a new retrieval algorithm was developed. This algorithm uses brightness temperatures (TBs) and TB anomalies together to accurately estimate TC surface pressure fields. Considering the relative superiority of 118‐GHz radiometers in spatial resolution, this study not only used the measurements of 60‐GHz radiometer Advanced Technology Microwave Sounder (ATMS) but also the 118‐GHz radiometer Microwave Humidity and Temperature Sounder (MWHTS). The TC measurements from July 2015 to September 2018 and the corresponding Global Data Assimilation System (GDAS) Final (FNL) analysis data were used to develop and test the retrieval algorithm. The testing results show that the proposed method can estimate the surface pressure fields of a TC's core area (within a 2° radius from the center) with an accuracy of better than 4.0, 5.0, and 8.0 hPa for tropical depressions and tropical storms, typhoons or hurricanes, and severe typhoons or major hurricanes, respectively. In addition, an in situ comparison demonstrates that the accuracy of the retrieved central pressure is better than 6.0, 8.0, and 10.0 hPa for tropical depressions and tropical storms, typhoons or hurricanes, and severe typhoons or major hurricanes, respectively.

Atmospheric Retrievals and Assessment for Microwave Observations from Chinese FY-3C Satellite during Hurricane Matthew

The evolution process of hurricane Matthew (NO. 8, 2016) was simulated using the mesoscale Weather Research and Forecasting (WRF) model at temporal resolution of 5 min and spatial resolution of 15 km. The atmospheric temperature and humidity profiles were retrieved accordingly for diagnostic analysis of the short-term heavy rainstorm. The satellite-based microwave observations from Microwave Humidity and Temperature Sounder (MWHTS) instrument on board the FY-3C polar-orbiting satellite were matched with the WRF grid points. In particular, the in-orbit calibration and data quality control are detailed, and an innovative method combining artificial neural network (ANN) and 1-D variational approach is presented to derive the high-performance retrieval profiles. Results show that the root-mean-square errors of the retrieved temperature and water vapor density profiles are 0.75 K and 0.41 g/m3, respectively. In addition, this study used both the retrievals and radiance from MWHTS as input to the WRF Data Assimilation (WRFDA) model to forecast the track and intensity of hurricane Matthew. The forecast results were cross-compared with the best track to verify the radiance quality and performance of the retrievals, especially for the 118 GHz channel, which was firstly used in meteorological satellite.

Performance Analysis of Microwave Humidity and Temperature Sounder Onboard the FY-3D Satellite From Prelaunch Multiangle Calibration Data in Thermal/Vacuum Test

A newly designed thermal/vacuum (T/V) prelaunch multiangle calibration test is proposed for Microwave Humidity and Temperature Sounder (MWHTS) onboard the Feng Yun 3D satellite. Compared with other existing prelaunch calibration tests designed at fix scan angle, this test is first proposed to analyze the measurements of MWHTS from multiscan angles. A set of comprehensive calibration method is established and used for calibration data processing. The high-quality data preprocessing methods are performed. Essential calibration coefficients such as cold bias, hot bias, and nonlinearity coefficients, and calibration results such as calibration residual error, sensitivity, and calibration accuracy of MWHTS are all obtained and analyzed in MWHTS’s six observing positions. The measured sensitivity value of channel 2 is 1.5 K while the measured sensitivities of the others range from 0.18 to 0.57 K. The calibration accuracy of channel 2 is 1.5 K while the calibration accuracies of the others range from 0.32 to 0.7 K. According to the discrepancy of multiangle calibration test results, the radiation leakage and the response lag for special channels are discovered for the first time in T/V test, and the reasons of these two special phenomena are fully analyzed. Moreover, the measurements of the T/V test with fast changing instrument temperatures are analyzed and the applicability of nonlinearity coefficients obtained in T/V test for in-orbit calibration is verified. In conclusion, MWHTS meets the basic design requirements of sensitivity and calibration accuracy, the changing of the MWHTS observing positions does not impact the calibration coefficients and results, and the nonlinearity coefficients obtained in T/V test are valid when instrument temperature experiences some fast changing.

Case Study of Atmospheric Retrievals of MWHTS aboard FY-3C Satellite

The mesoscale numerical model WRF is used to simulate the No. 8 hurricane Matthew in 2016. The radar and radiometer observations are assimilated by WRF Var. With the verification to the real situation, the process of the hurricane rainstorm is well simulated by WRF in this case that it could basically show the hurricane evolution. We use the simulation results which are model outputs with high spatial and temporal resolution to do diagnostic analysis on the short term heavy rainstorm caused by Matthew, with a comparison between the best track and forecasting tracks using active and passive microwave observations from WRFDA model. In order to analyze the inner structure, the nadiral satellite-based observations were matched between the Microwave Humidity and Temperature Sounder (MWHTS) instrument aboard the FY-3C polar-orbiting platform since Sept 30, 2013 and dual-frequency radar named PR aboard GPM satellite and then separate retrievals are demonstrated in data assimilation for extreme weather with the retrieved root-mean-square errors of about 0.9 K and 17% and 10 mm/h for precipitation products, which demonstrates the impact of 118 GHz observations in data assimilation model.

Precipitation Retrieval Using 118.75-GHz and 183.31-GHz Channels From MWHTS on FY-3C Satellite

In this paper, the focus is on precipitation rate retrieval using 118.75 and 183.31-GHz channels from the microwave humidity and temperature sounder (MWHTS) onboard the FY-3C satellite. These channels provide not only atmospheric humidity profile measurements but they also provide temperature profile measurements. These measurements play important roles detecting and retrieving precipitation rates. Data from the MWHTS and the Tropical Rainfall Measuring Mission Multisatellite Precipitation Analysis (TMPA) 3B42 are matched in time and space. Matched datasets are used to verify precipitation detection algorithms and precipitation rate retrieval algorithms. To retrieve the precipitation rate, the multiple linear regression algorithm and back propagation (BP) neutral network algorithm are applied in the ten models proposed in this paper. After detailed retrieval analysis between these two algorithms, advanced algorithms are presented this paper to improve the accuracy of the precipitation rate retrieval. In our algorithms, the correlation coefficient of the precipitation rate over the ocean can reach 0.82, the bias is approximately 0.07 mm/hr, and the root mean square error (RMSe) is less than 0.4 mm/hr. Over land, the correlation coefficient is approximately 0.73, the bias is 0.1 mm/hr, and the RMSe is less than 0.5 mm/hr. These results show that our retrieval algorithms improve the retrieval accuracy. Moreover, we study a number of typhoons and find that the FY-3C MWHTS works well to retrieve typhoon precipitation rates. The potential sensitivities of the temperature and humidity channels are analyzed, which can improve the retrieval accuracy and lay the foundation for further research.

Precipitation Retrievals in typhoon domain combining of FY3C MWHTS Observations and WRF Predicted Models

A passive sub-millimeter precipitation retrievals algorithm is provided based on Microwave Humidity and Temperature Sounder (MWHTS) onboard the Chinese Feng Yun 3C (FY-3C) satellite. Using the validated global reference physical model NCEP/WRF/VDISORT), NCEP data per 6 hours are downloaded to run the Weather Research and Forecast model WRF, and derive the typical precipitation data from the whole world. The precipitation retrieval algorithm can operate either on land or on seawater for global. To simply the calculation procedure and save the training time, principle component analysis (PCA) was adapted to filter out the redundancy caused by scanning angle and surface effects, as well as system noise. According to the comparison and validation combing with other precipitation sources, it is demonstrated that the retrievals are reliable for surface precipitation rate higher than 0.1 mm/h at 15km resolution.

Bias Correction for Retrieval of Atmospheric Parameters from the Microwave Humidity and Temperature Sounder Onboard the Fengyun-3C Satellite

The microwave humidity and temperature sounder (MWHTS) on the Fengyun (FY)-3C satellite measures the outgoing radiance from the Earth’s surface and atmospheric constituents. MWHTS, which makes measurements in the isolated oxygen absorption line near 118 GHz and the vicinity of the strong water vapor absorption line around 183 GHz, can provide fine vertical distribution structures of both atmospheric humidity and temperature. However, in order to obtain the accurate soundings of humidity and temperature by physical retrieval methods, the bias between the observed and simulated radiance calculated by the radiative transfer model from the background or first guess profiles must be corrected. In this study, two bias correction methods are developed through the correlation analysis between MWHTS measurements and air mass identified by the first guess profiles of the physical inversion; one is the linear regression correction (LRC), and the other is the neural network correction (NNC), representing the linear and nonlinear relationships between MWHTS measurements and air mass, respectively. The correction methods have been applied to MWHTS observed brightness temperatures over the geographic area (180° W–180° E, 60° S–60° N). The corrected results are evaluated by the probability density function of the differences between corrected observations and simulated values and the root mean square errors (RMSE) with respect to simulated observations. The numerical results show that the NNC method has better performance, especially in MWHTS Channels 1 and 7–9, whose peak weight function heights are close to the surface. In order to assess the effects of bias correction methods proposed in this study on the retrieval accuracy, a one-dimensional variational system was built and applied to the MWHTS brightness temperatures to estimate the atmospheric temperature and humidity profiles. The retrieval results also show that NNC has better performance. An indication of the stability and robustness of the NNC method is given, which suggests that the NNC method has promising application perspectives in the physical retrieval.

Regional Profiles and Precipitation Retrievals and Analysis Using FY-3C MWHTS

The 89 and 150 GHz channels operated in window are sensitive to precipitation and humidity. The 183 GHz humidity-sensitive channels and 118 GHz temperature-sensitive channels of the Microwave Humidity and Temperature Sounder (MWHTS) on the Chinese Feng Yun 3C MWHTS (FY-3C MWHTS) polar-orbit meteorological satellite responds in part to precipitation. Combining 118 and 183 GHz channels, the paper develops a passive sub-millimeter atmospheric profile and precipitation retrievals algorithm for MWHTS onboard the FY-3C (Feng Yun-3C) satellite. The retrieval algorithm employs a number of back propagation neural network estimators trained and evaluated using the validated global reference physical model NCEP/WRF/ARTS and works for land and seawater with latitude between -40 to 40 degree. NCEP data per 6 hours were downloaded to run the Weather Research and Forecast model WRF, and to derive the typical precipitation data for the whole world. The Atmospheric Radiative Transfer Simulator ARTS is feasible for performing simulations of atmospheric radiative transfer. The results show that the profile retrievals using BP-NN algorithm has the best correlation with those from radiosonde, which is less than 18% and 1 K of root mean square error, respectively. For precipitation rate retrievals, a much better agreement is reached with rain gauge and ECMWF datasets, the RMS is between 0.80 to 30.24 mm/h for sea surface and 0.789 to 33.11 mm/h for land surface according to the classification by precipitation type. Also, the analysis of retrievals located in Tibetan plateau is provided as an example to justify the robustness and performance of retrieving model.