This paper proposes an optimal,robust,and efficient guidance scheme for the perturbed minimum-time low-thrust transfer toward the geostationary orbit.The Earth’s oblateness perturbation and shadow are taken into acco...This paper proposes an optimal,robust,and efficient guidance scheme for the perturbed minimum-time low-thrust transfer toward the geostationary orbit.The Earth’s oblateness perturbation and shadow are taken into account.It is difficult for a Lyapunov-based or trajectory-tracking guidance method to possess multiple characteristics at the same time,including high guidance optimality,robustness,and onboard computational efficiency.In this work,a concise relationship between the minimum-time transfer problem with orbital averaging and its optimal solution is identified,which reveals that the five averaged initial costates that dominate the optimal thrust direction can be approximately determined by only four initial modified equinoctial orbit elements after a coordinate transformation.Based on this relationship,the optimal averaged trajectories constituting the training dataset are randomly generated around a nominal averaged trajectory.Five polynomial regression models are trained on the training dataset and are regarded as the costate estimators.In the transfer,the spacecraft can obtain the real-time approximate optimal thrust direction by combining the costate estimations provided by the estimators with the current state at any time.Moreover,all these computations onboard are analytical.The simulation results show that the proposed guidance scheme possesses extremely high guidance optimality,robustness,and onboard computational efficiency.展开更多
Convective storms and lightning are among the most important weather phenomena that are challenging to forecast.In this study,a novel multi-task learning(MTL)encoder-decoder U-net neural network was developed to forec...Convective storms and lightning are among the most important weather phenomena that are challenging to forecast.In this study,a novel multi-task learning(MTL)encoder-decoder U-net neural network was developed to forecast convective storms and lightning with lead times for up to 90 min,using GOES-16 geostationary satellite infrared brightness temperatures(IRBTs),lightning flashes from Geostationary Lightning Mapper(GLM),and vertically integrated liquid(VIL)from Next Generation Weather Radar(NEXRAD).To cope with the heavily skewed distribution of lightning data,a spatiotemporal exponent-weighted loss function and log-transformed lightning normalization approach were developed.The effects of MTL,single-task learning(STL),and IRBTs as auxiliary input features on convection and lightning nowcasting were investigated.The results showed that normalizing the heavily skew-distributed lightning data along with a log-transformation dramatically outperforms the min-max normalization method for nowcasting an intense lightning event.The MTL model significantly outperformed the STL model for both lightning nowcasting and VIL nowcasting,particularly for intense lightning events.The MTL also helped delay the lightning forecast performance decay with the lead times.Furthermore,incorporating satellite IRBTs as auxiliary input features substantially improved lightning nowcasting,but produced little difference in VIL forecasting.Finally,the MTL model performed better for forecasting both lightning and the VIL of organized convective storms than for isolated cells.展开更多
The paper describes the development of mobile communication first and then points out that it is necessary for China to develop satellite mobile communication after comparing the cellular mobile communication with the...The paper describes the development of mobile communication first and then points out that it is necessary for China to develop satellite mobile communication after comparing the cellular mobile communication with the satellite mobile communication. After comparing the geostationary satellite system with the low earth orbit satellite mobile communication system, as well as the single-beam system with the multibeams system, both used in satellite mobile communication, we suggest that China, according to its economic status and level of satellite technology, should develop a geostationary multibeam satellite for its domestic mobile communication.展开更多
A novel and efficient method to evaluate the transmission control protocol (TCP) performance over satellite links is presented. A TCP module is divided into three functional blocks, namely data processing, congestio...A novel and efficient method to evaluate the transmission control protocol (TCP) performance over satellite links is presented. A TCP module is divided into three functional blocks, namely data processing, congestion control and error control The re-established TCP module is easy to update TCP congestion control strategy or error control strategy. With the proposed analysis approach, the interactions between different congestion control and error control mechanisms, as well as the performanee of various combination protocols in satellite environments have been investigated. Simulation results obtained through a series of experiments have shown that SNACK-based error control strategy can perform well with any other congestion control strategy. The best performanee can be achieved by TCP NewReno congestion control strategy and SNACK-based error control strategy.展开更多
Satellite link characteristics drastically degrade transport control protocol (TCP) performance. An efficient performance enhancing scheme is proposed. The improvement of TCP performance over satellite-based Interue...Satellite link characteristics drastically degrade transport control protocol (TCP) performance. An efficient performance enhancing scheme is proposed. The improvement of TCP performance over satellite-based Interuet is accomplished by protocol transition gateways at each end of a satellite link. The protocol which runs over a satellite link executes the receiver-driven flow control and acknowledgements- and timeouts-based error control strategies. The validity of this TCP performance enhancing scheme is verified by a series of simulation experiments. Results show that the proposed scheme can efficiently enhance the TCP performance over satellite-based Internet and ensure that the available bandwidth resources of the satellite link are fully utilized.展开更多
Fengyun-4A(FY-4A), the first of the Chinese next-generation geostationary meteorological satellites, launched in2016, offers several advances over the FY-2: more spectral bands, faster imaging, and infrared hypersp...Fengyun-4A(FY-4A), the first of the Chinese next-generation geostationary meteorological satellites, launched in2016, offers several advances over the FY-2: more spectral bands, faster imaging, and infrared hyperspectral measurements. To support the major objective of developing the prototypes of FY-4 science algorithms, two science product algorithm testbeds for imagers and sounders have been developed by the scientists in the FY-4 Algorithm Working Group(AWG). Both testbeds, written in FORTRAN and C programming languages for Linux or UNIX systems, have been tested successfully by using Intel/g compilers. Some important FY-4 science products, including cloud mask, cloud properties, and temperature profiles, have been retrieved successfully through using a proxy imager, Himawari-8/Advanced Himawari Imager(AHI), and sounder data, obtained from the Atmospheric Infra Red Sounder, thus demonstrating their robustness. In addition, in early 2016, the FY-4 AWG was developed based on the imager testbed—a near real-time processing system for Himawari-8/AHI data for use by Chinese weather forecasters.Consequently, robust and flexible science product algorithm testbeds have provided essential and productive tools for popularizing FY-4 data and developing substantial improvements in FY-4 products.展开更多
This paper proposes several quantitative characteristics to study convective systems using observations from Doppler weather radars and geostationary satellites. Specifically, in order to measure the convective intens...This paper proposes several quantitative characteristics to study convective systems using observations from Doppler weather radars and geostationary satellites. Specifically, in order to measure the convective intensity of each system, a new index, named the "Convective Intensity Ratio" (CIR), is defined as the ratio between the area of strong radar echoes at the upper level and the size of the convective cell itself. Based on these quantitative characteristics, the evolution of convective cells, surface rainfall intensity, rainfall area and convectively generated anvil clouds can be studied, and the relationships between them can also be analyzed. After testing nine meso-β-scale convective systems over North China during 2006–2007, the results were as follows: (1) the CIR was highly correlated with surface rainfall intensity, and the correlation reached a maximum when the CIR led rainfall intensity by 6–30 mins. The maximum CIR could be at most ~30 mins before the maximum rainfall intensity. (2) Convective systems with larger maximum CIRs usually had colder cloud-tops. (3) The maximum area of anvil cloud appeared 0.5–1.5 h after rainfall intensity began to weaken. The maximum area of anvil cloud and the time lag between maximum rainfall intensity and the maximum area of anvil cloud both increased with the CIR.展开更多
Based on Multifunctional Transport Satellite data and the infrared window-texture detection algorithm, the level of overshooting top(OT) activity within a tropical cyclone(TC), which is defined as the hourly mean ...Based on Multifunctional Transport Satellite data and the infrared window-texture detection algorithm, the level of overshooting top(OT) activity within a tropical cyclone(TC), which is defined as the hourly mean number of OT occurrence,was statistically investigated in the western North Pacific basin for the period 2005–12. Based on the level of OT activity,the samples were divided into OT and non-OT cases or high-activity-OT(HA-OT) and low-activity-OT(LA-OT) cases. The differences in large-scale environmental variables between OT(HA-OT) and non-OT(LA-OT) cases were examined 12 hours prior to the OT occurrence. Statistical analysis showed that environmental differences did exist between the OT and non-OT cases. The OTs were more skewed towards the early stage of the TC life cycle, and mostly concentrated in low latitudes.Meanwhile, a sufficiently deep warm-water layer, large temperature difference between the upper- and lower-level troposphere, large humidity at the middle and upper levels, and large atmospheric instability, were favorable for OT occurrence.The differences in large-scale environmental characteristics between HA-OTs and LA-OTs were not as significant as those between OTs and non-OTs, but the HA-OT samples tended to occur when the vertical shear was weak and the TC intensity was low. Finally, statistical models were designed to predict the OT and HA-OT. When at least three OT(HA-OT) predictor thresholds were satisfied, the Peirce skill score reached a maximum value of 0.49(0.30).展开更多
The visibility for low earth orbit(LEO) satellites provided by the BeiDou-2 system is analyzed and compared with the global positioning system(GPS). In addition, the spaceborne receivers' observations are simulat...The visibility for low earth orbit(LEO) satellites provided by the BeiDou-2 system is analyzed and compared with the global positioning system(GPS). In addition, the spaceborne receivers' observations are simulated by the BeiDou satellites broadcast ephemeris and LEO satellites orbits. The precise orbit determination(POD) results show that the along-track component accuracy is much better over the service area than the non-service area, while the accuracy of the other two directions keeps at the same level over different areas. However, the 3-dimensional(3D) accuracy over the two areas shows almost no difference. Only taking into consideration the observation noise and navigation satellite ephemeris errors, the 3D accuracy of the POD is about30 cm. As for the precise relative orbit determination(PROD), the 3D accuracy is much better over the eastern hemisphere than that of the western hemisphere. The baseline length accuracy is 3.4 mm over the service area, and it is still better than 1 cm over the non-service area. This paper demonstrates that the BeiDou regional constellation could provide global service to LEO satellites for the POD and the PROD. Finally, the benefit of geostationary earth orbit(GEO) satellites is illustrated for POD.展开更多
A method(Rieland,1985)has been modified to determine the downward solar radiation at ground over East Asia,using GMS-3 data of the satellite with a spatial resolution of 10×10 krn^2 and a time interval of 3 hours...A method(Rieland,1985)has been modified to determine the downward solar radiation at ground over East Asia,using GMS-3 data of the satellite with a spatial resolution of 10×10 krn^2 and a time interval of 3 hours.The distributions of the monthly mean global radiation are obtained for January,April,July and October of 1985.These results illustrate that the topography effect of the Tibetan Plateau is not negligible.The values of global radiation over the high Tibetan Plateau during all seasons are higher than those in the lower-level surroundings.By comparing model results with ground observed data, the relative errors in monthly averages of global radiation are 2.8% for clear sky and 6.3%,5.3%,5.0% and 4.5% for cloudy sky in January,April, July and October,respectively.The relative error in daily global radiation during the snow-free season is less than 20% and larger than 20% in snow-covered winter.We,however,had no data for these comparisons which were measured directly at the Plateau during the year 1985.展开更多
Snow and cloud discrimination is a main factor contributing to errors in satellite-based snow cover.To address the error,satellite-based snow cover performs snow reclassification tests on the cloud pixels of the cloud...Snow and cloud discrimination is a main factor contributing to errors in satellite-based snow cover.To address the error,satellite-based snow cover performs snow reclassification tests on the cloud pixels of the cloud mask,but the error still remains.Machine Learning(ML)has recently been applied to remote sensing to calculate satellite-based meteorological data,and its utility has been demonstrated.In this study,snow and cloud discrimination errors were analyzed for GK-2A/AMI snow cover,and ML models(Random Forest and Deep Neural Network)were applied to accurately distinguish snow and clouds.The ML-based snow reclassified was integrated with the GK-2A/AMI snow cover through post-processing.We used the S-NPP/VIIRS snow cover and ASOS in situ snow observation data,which are satellite-based snow cover and ground truth data,as validation data to evaluate whether the snow/cloud discrimination is improved.The ML-based integrated snow cover detected 33–53%more snow compared to the GK-2A/AMI snow cover.In terms of performance,the F1-score and overall accuracy of the GK-2A/AMI snow cover was 73.06%and 89.99%,respectively,and those of the integrated snow cover were 76.78–78.28%and 90.93–91.26%,respectively.展开更多
Satellite microwave thermal emissions mixed with signals from active sensors are referred to as radio- frequency interference (RFI). Based on Advanced Micro- wave Scanning Radiometer-Earth Observing System (AMSR-E...Satellite microwave thermal emissions mixed with signals from active sensors are referred to as radio- frequency interference (RFI). Based on Advanced Micro- wave Scanning Radiometer-Earth Observing System (AMSR-E) observations from June 1 to 16, 2011, RFI over Europe was identified and analyzed using the modified principal component analysis algorithm in this paper. The X band AMSR-E measurements in England and Italy are mostly affected by the stable, persistent, active microwave transmitters on the surface, while the RFI source of other European countries is the interference of the reflected geostationary TV satellite downlink signals to the measurements of spacebome microwave radiometers. The locations and intensities of the RFI induced by the geostationary TV and communication satellites changed with time within the observed period. The observations of spacebome microwave radiometers in ascending portions of orbits are usually interfered with over European land, while no RFI was detected in descending passes. The RFI locations and intensities from the reflection of downlink radiation are highly dependent upon the relative geometry between the geostationary satellite and the measuring passive sensor. Only these fields of view of a spaceborne instrument whose scan azimuths are close to the azimuth relative to the geostationary satellite are likely to be affected by RFI.展开更多
Some typical samples are used to explore the quantitative correlation with their features between a convective cloud and its rainfall field,with which to develop two morphological functions for the correlation and by ...Some typical samples are used to explore the quantitative correlation with their features between a convective cloud and its rainfall field,with which to develop two morphological functions for the correlation and by singling out their most suitable groups of parameters we propose a model for quantitatively estimating precipitation in the context o{ the in-advance recognition of meso-α convective system properties and its precipitating center.From the model fitting precision and forecasting accuracy we find that it is feasible to utilize geostationary meteorological satellite (GMS) digitalized imagery for estimating short-term rainfall in a quantitative manner.Also,evidence suggests that the model is supposed to be restricted in its applicability due to the fact that the employed samples are from rather typical rainfall events that are large-scale,slow-moving and have well-defined genesis and dissipative stages.展开更多
A spiral cloud belt matching(SCBeM)technique is proposed for automatically locating the tropical cyclone(TC)center position on the basis of multi-band geo-satellite images.The technique comprises four steps:fusion of ...A spiral cloud belt matching(SCBeM)technique is proposed for automatically locating the tropical cyclone(TC)center position on the basis of multi-band geo-satellite images.The technique comprises four steps:fusion of multi-band geo-satellite images,extraction of TC cloud systems,construction of a spiral cloud belt template(CBT),and template matching to locate the TC center.In testing of the proposed SCBeM technique on 97 TCs over the western North Pacific during 2012-2015,the median error(ME)was 50 km.An independent test of another 29 TCs in 2016 resulted in a ME of 54 km.The SCBeM performs better for TCs with intensity above“typhoon”level than it does for weaker systems,and is not suitable for use on high-latitude or landfall TCs if their cloud band formations have been destroyed by westerlies or by terrain.The proposed SCBeM technique provides an additional solution for automatically and objectively locating the TC center and has the potential to be applied conveniently in an operational setting.Intercomparisons between the Automated Rotational Center Hurricane Eye Retrieval(ARCHER)and SCBeM methods using events from 2014 to 2016 reveal that ARCHER has better location accuracy.However,when IR imagery alone is used,the ME of SCBeM is 54 km,and in the case of low latitudes and low vertical wind shear the ME is 45-47 km,which approaches that of ARCHER(49 km).Thus,the SCBeM method is simple,has good time resolution,performs well and is a better choice for those TC operational agencies in the case that the microwave images,ASCAT,or other observations are unavailable.展开更多
This paper extends a new temperature and emissivity separation(TES)algorithm for retrieving land surface temperature and emissivity(LST and LSE)to the Advanced Geosynchronous Radiation Imager(AGRI)onboard Fengyun-4A,C...This paper extends a new temperature and emissivity separation(TES)algorithm for retrieving land surface temperature and emissivity(LST and LSE)to the Advanced Geosynchronous Radiation Imager(AGRI)onboard Fengyun-4A,China’s newest geostationary meteorological satellite.The extended TES algorithm was named the AGRI TES algorithm.The AGRI TES algorithm employs a modified water vapor scaling(WVS)method and a recalibrated empirical function over vegetated surfaces.In situ validation and cross-validation are utilized to investigate the accuracy of the retrieved LST and LSE.LST validation using the collected field measurements showed that the mean bias and RMSE of AGRI TES LST are 0.58 and 2.93 K in the daytime and−0.30 K and 2.18 K at nighttime,respectively;the AGRI official LST is systematically underestimated.Compared with the MODIS LST and LSE products(MYD21),the average bias and RMSE of AGRI TES LST are−0.26 K and 1.65 K,respectively.The AGRI TES LSE outperforms the AGRI official LSE in terms of accuracy and spatial integrity.This study demonstrates the good performance of the AGRI TES algorithm for the retrieval of high-quality LST and LSE,and the potential of the AGRI TES algorithm in producing operational LST and LSE products.展开更多
By use of GMS-4 infrared brightness temperature and visible albedo data from January to February in 1995,the method for extracting of sea ice parameters is developed.The digital remote sensing picture is obtained on L...By use of GMS-4 infrared brightness temperature and visible albedo data from January to February in 1995,the method for extracting of sea ice parameters is developed.The digital remote sensing picture is obtained on Liaodong Bay.Based on the difference in physical properties between ice and water,a criterion distinguishing ice from water is set up.Ice thickness has been calculated according to the relationship between ice thickness and brightness as well as albedo.Ice concentration is retrieved due to the difference on albedo between ice and water.The results indicate that the accuracy of ice-water distinguishing is 84.8%,the errors of ice thickness and ice concentration are 3.8 cm and 22%,respectively.展开更多
To study the possibility of improving the precision of retrieving precipitation through GMS-5 infrared data,the relationship between the data of GMS-5 infrared channel 1(IR1)and precipitation sounded by TRMM/PR was ca...To study the possibility of improving the precision of retrieving precipitation through GMS-5 infrared data,the relationship between the data of GMS-5 infrared channel 1(IR1)and precipitation sounded by TRMM/PR was carefully studied through some cases gathered during the HUBEX 1998.First of all,the relationship between the brightness temperature(Tb)and PR- sounded near-surface rainfall rate(NSRR)was studied.Then,as PR can sound the inner structure of rainfall area.a unique advantage of this new instrument,the relationship between Tb and PR-sounded rainfall rate in each layer was also studied.Still,as PR can tell the rain type, those relationships were studied again according to the different types of precipitation(i.e. convective and stratiform).After comparing these outcomes with those from other references,it can be concluded that the relationship between Tb and PR-sounded rainfall rate is acceptable and it is possible to calibrate precipitation retrieved through Tb by PR data.展开更多
Geostationary Operational Environmental Satellite-16(GOES-16) Advanced Baseline Imager(ABI) observations of brightness temperature(TB) are used to examine the temporal evolutions of convection-affected structures of H...Geostationary Operational Environmental Satellite-16(GOES-16) Advanced Baseline Imager(ABI) observations of brightness temperature(TB) are used to examine the temporal evolutions of convection-affected structures of Hurricane Irma(2017) during its rapid intensification(RI) period from 0600 to 1800 UTC 4 September 2017.The ABI observations reveal that both an elliptical eye and a spiral rainband that originated from Irma's eyewall obviously exhibit wavenumber-2 TB asymmetries.The elliptical eye underwent a counterclockwise rotation at a mean speed of a wavenumber-2 vortex Rossby edge wave from 0815 to 1005 UTC 4 September.In the following about 2 hours(1025–1255 UTC 4 September),an inner spiral rainband originated from the eyewall and propagated at a phase speed that approximates the vortex Rossby wave(VRW) phase speed calculated from the aircraft reconnaissance data.During the RI period of Irma,ABI TB observations show an on–off occurrence of low TB intrusions into the eye,accompanying a phase lock of eyewall TB asymmetries of wavenumbers 1 and 2 and an outward propagation of VRW-like inner spiral rainbands from the eyewall.The phase lock leads to an energy growth of Irma's eyewall asymmetries.Although the eye remained clear from 1415 to 1725 UTC 4 September,an inner spiral rainband that originated from a large convective area also had a VRW-like outward propagation,which is probably due to a vertical tilt of Irma.This study suggests a potential link between convection sensitive GOES imager observations and hurricane dynamics.展开更多
基金supported by the National Natural Science Foundation of China(No.12022214)the National Key R&D Program of China(No.2020YFC2201200)。
文摘This paper proposes an optimal,robust,and efficient guidance scheme for the perturbed minimum-time low-thrust transfer toward the geostationary orbit.The Earth’s oblateness perturbation and shadow are taken into account.It is difficult for a Lyapunov-based or trajectory-tracking guidance method to possess multiple characteristics at the same time,including high guidance optimality,robustness,and onboard computational efficiency.In this work,a concise relationship between the minimum-time transfer problem with orbital averaging and its optimal solution is identified,which reveals that the five averaged initial costates that dominate the optimal thrust direction can be approximately determined by only four initial modified equinoctial orbit elements after a coordinate transformation.Based on this relationship,the optimal averaged trajectories constituting the training dataset are randomly generated around a nominal averaged trajectory.Five polynomial regression models are trained on the training dataset and are regarded as the costate estimators.In the transfer,the spacecraft can obtain the real-time approximate optimal thrust direction by combining the costate estimations provided by the estimators with the current state at any time.Moreover,all these computations onboard are analytical.The simulation results show that the proposed guidance scheme possesses extremely high guidance optimality,robustness,and onboard computational efficiency.
基金supported by the Science and Technology Grant No.520120210003,Jibei Electric Power Company of the State Grid Corporation of China。
文摘Convective storms and lightning are among the most important weather phenomena that are challenging to forecast.In this study,a novel multi-task learning(MTL)encoder-decoder U-net neural network was developed to forecast convective storms and lightning with lead times for up to 90 min,using GOES-16 geostationary satellite infrared brightness temperatures(IRBTs),lightning flashes from Geostationary Lightning Mapper(GLM),and vertically integrated liquid(VIL)from Next Generation Weather Radar(NEXRAD).To cope with the heavily skewed distribution of lightning data,a spatiotemporal exponent-weighted loss function and log-transformed lightning normalization approach were developed.The effects of MTL,single-task learning(STL),and IRBTs as auxiliary input features on convection and lightning nowcasting were investigated.The results showed that normalizing the heavily skew-distributed lightning data along with a log-transformation dramatically outperforms the min-max normalization method for nowcasting an intense lightning event.The MTL model significantly outperformed the STL model for both lightning nowcasting and VIL nowcasting,particularly for intense lightning events.The MTL also helped delay the lightning forecast performance decay with the lead times.Furthermore,incorporating satellite IRBTs as auxiliary input features substantially improved lightning nowcasting,but produced little difference in VIL forecasting.Finally,the MTL model performed better for forecasting both lightning and the VIL of organized convective storms than for isolated cells.
文摘The paper describes the development of mobile communication first and then points out that it is necessary for China to develop satellite mobile communication after comparing the cellular mobile communication with the satellite mobile communication. After comparing the geostationary satellite system with the low earth orbit satellite mobile communication system, as well as the single-beam system with the multibeams system, both used in satellite mobile communication, we suggest that China, according to its economic status and level of satellite technology, should develop a geostationary multibeam satellite for its domestic mobile communication.
文摘A novel and efficient method to evaluate the transmission control protocol (TCP) performance over satellite links is presented. A TCP module is divided into three functional blocks, namely data processing, congestion control and error control The re-established TCP module is easy to update TCP congestion control strategy or error control strategy. With the proposed analysis approach, the interactions between different congestion control and error control mechanisms, as well as the performanee of various combination protocols in satellite environments have been investigated. Simulation results obtained through a series of experiments have shown that SNACK-based error control strategy can perform well with any other congestion control strategy. The best performanee can be achieved by TCP NewReno congestion control strategy and SNACK-based error control strategy.
文摘Satellite link characteristics drastically degrade transport control protocol (TCP) performance. An efficient performance enhancing scheme is proposed. The improvement of TCP performance over satellite-based Interuet is accomplished by protocol transition gateways at each end of a satellite link. The protocol which runs over a satellite link executes the receiver-driven flow control and acknowledgements- and timeouts-based error control strategies. The validity of this TCP performance enhancing scheme is verified by a series of simulation experiments. Results show that the proposed scheme can efficiently enhance the TCP performance over satellite-based Internet and ensure that the available bandwidth resources of the satellite link are fully utilized.
基金National Natural Science Foundation(41405035,41571348,and 41405038)China Meteorological Administration Special Public Welfare Research Fund(GYHY201406011 and GYHY201506074)
文摘Fengyun-4A(FY-4A), the first of the Chinese next-generation geostationary meteorological satellites, launched in2016, offers several advances over the FY-2: more spectral bands, faster imaging, and infrared hyperspectral measurements. To support the major objective of developing the prototypes of FY-4 science algorithms, two science product algorithm testbeds for imagers and sounders have been developed by the scientists in the FY-4 Algorithm Working Group(AWG). Both testbeds, written in FORTRAN and C programming languages for Linux or UNIX systems, have been tested successfully by using Intel/g compilers. Some important FY-4 science products, including cloud mask, cloud properties, and temperature profiles, have been retrieved successfully through using a proxy imager, Himawari-8/Advanced Himawari Imager(AHI), and sounder data, obtained from the Atmospheric Infra Red Sounder, thus demonstrating their robustness. In addition, in early 2016, the FY-4 AWG was developed based on the imager testbed—a near real-time processing system for Himawari-8/AHI data for use by Chinese weather forecasters.Consequently, robust and flexible science product algorithm testbeds have provided essential and productive tools for popularizing FY-4 data and developing substantial improvements in FY-4 products.
基金supported bythe National High Technology Research and Development Program of China (Grant No. 2006AA122106)the Na-tional Natural Science Foundation of China (Grant No.40875019) the Foundation of Basic Scientific Researchand Operation of Chinese Academy of Meteorological Sci-ence (Grant No. 2007Y004)
文摘This paper proposes several quantitative characteristics to study convective systems using observations from Doppler weather radars and geostationary satellites. Specifically, in order to measure the convective intensity of each system, a new index, named the "Convective Intensity Ratio" (CIR), is defined as the ratio between the area of strong radar echoes at the upper level and the size of the convective cell itself. Based on these quantitative characteristics, the evolution of convective cells, surface rainfall intensity, rainfall area and convectively generated anvil clouds can be studied, and the relationships between them can also be analyzed. After testing nine meso-β-scale convective systems over North China during 2006–2007, the results were as follows: (1) the CIR was highly correlated with surface rainfall intensity, and the correlation reached a maximum when the CIR led rainfall intensity by 6–30 mins. The maximum CIR could be at most ~30 mins before the maximum rainfall intensity. (2) Convective systems with larger maximum CIRs usually had colder cloud-tops. (3) The maximum area of anvil cloud appeared 0.5–1.5 h after rainfall intensity began to weaken. The maximum area of anvil cloud and the time lag between maximum rainfall intensity and the maximum area of anvil cloud both increased with the CIR.
基金partially supported by the National Fundamental Research(973)Program of China(Grant Nos.2013CB430100 and 2015CB452800)the National Natural Science Foundation of China(Grant Nos.41275057 and 41505086)
文摘Based on Multifunctional Transport Satellite data and the infrared window-texture detection algorithm, the level of overshooting top(OT) activity within a tropical cyclone(TC), which is defined as the hourly mean number of OT occurrence,was statistically investigated in the western North Pacific basin for the period 2005–12. Based on the level of OT activity,the samples were divided into OT and non-OT cases or high-activity-OT(HA-OT) and low-activity-OT(LA-OT) cases. The differences in large-scale environmental variables between OT(HA-OT) and non-OT(LA-OT) cases were examined 12 hours prior to the OT occurrence. Statistical analysis showed that environmental differences did exist between the OT and non-OT cases. The OTs were more skewed towards the early stage of the TC life cycle, and mostly concentrated in low latitudes.Meanwhile, a sufficiently deep warm-water layer, large temperature difference between the upper- and lower-level troposphere, large humidity at the middle and upper levels, and large atmospheric instability, were favorable for OT occurrence.The differences in large-scale environmental characteristics between HA-OTs and LA-OTs were not as significant as those between OTs and non-OTs, but the HA-OT samples tended to occur when the vertical shear was weak and the TC intensity was low. Finally, statistical models were designed to predict the OT and HA-OT. When at least three OT(HA-OT) predictor thresholds were satisfied, the Peirce skill score reached a maximum value of 0.49(0.30).
基金co-supported by the National Natural Science Foundation of China (Nos: 61002033, 61370013)the Program for New Century Excellent Talents in University and the Scientific Research Foundation for the Returned Overseas Chinese Scholars of Ministry of Education of China
文摘The visibility for low earth orbit(LEO) satellites provided by the BeiDou-2 system is analyzed and compared with the global positioning system(GPS). In addition, the spaceborne receivers' observations are simulated by the BeiDou satellites broadcast ephemeris and LEO satellites orbits. The precise orbit determination(POD) results show that the along-track component accuracy is much better over the service area than the non-service area, while the accuracy of the other two directions keeps at the same level over different areas. However, the 3-dimensional(3D) accuracy over the two areas shows almost no difference. Only taking into consideration the observation noise and navigation satellite ephemeris errors, the 3D accuracy of the POD is about30 cm. As for the precise relative orbit determination(PROD), the 3D accuracy is much better over the eastern hemisphere than that of the western hemisphere. The baseline length accuracy is 3.4 mm over the service area, and it is still better than 1 cm over the non-service area. This paper demonstrates that the BeiDou regional constellation could provide global service to LEO satellites for the POD and the PROD. Finally, the benefit of geostationary earth orbit(GEO) satellites is illustrated for POD.
文摘A method(Rieland,1985)has been modified to determine the downward solar radiation at ground over East Asia,using GMS-3 data of the satellite with a spatial resolution of 10×10 krn^2 and a time interval of 3 hours.The distributions of the monthly mean global radiation are obtained for January,April,July and October of 1985.These results illustrate that the topography effect of the Tibetan Plateau is not negligible.The values of global radiation over the high Tibetan Plateau during all seasons are higher than those in the lower-level surroundings.By comparing model results with ground observed data, the relative errors in monthly averages of global radiation are 2.8% for clear sky and 6.3%,5.3%,5.0% and 4.5% for cloudy sky in January,April, July and October,respectively.The relative error in daily global radiation during the snow-free season is less than 20% and larger than 20% in snow-covered winter.We,however,had no data for these comparisons which were measured directly at the Plateau during the year 1985.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)[grant number 2021R1A2C2010976].
文摘Snow and cloud discrimination is a main factor contributing to errors in satellite-based snow cover.To address the error,satellite-based snow cover performs snow reclassification tests on the cloud pixels of the cloud mask,but the error still remains.Machine Learning(ML)has recently been applied to remote sensing to calculate satellite-based meteorological data,and its utility has been demonstrated.In this study,snow and cloud discrimination errors were analyzed for GK-2A/AMI snow cover,and ML models(Random Forest and Deep Neural Network)were applied to accurately distinguish snow and clouds.The ML-based snow reclassified was integrated with the GK-2A/AMI snow cover through post-processing.We used the S-NPP/VIIRS snow cover and ASOS in situ snow observation data,which are satellite-based snow cover and ground truth data,as validation data to evaluate whether the snow/cloud discrimination is improved.The ML-based integrated snow cover detected 33–53%more snow compared to the GK-2A/AMI snow cover.In terms of performance,the F1-score and overall accuracy of the GK-2A/AMI snow cover was 73.06%and 89.99%,respectively,and those of the integrated snow cover were 76.78–78.28%and 90.93–91.26%,respectively.
基金This work was jointly supported by the National Natural Science Foundation of China (Grant No. 41175034) and Key University Science Research Project of Jiangsu Province (No. 13KJA 170003).
文摘Satellite microwave thermal emissions mixed with signals from active sensors are referred to as radio- frequency interference (RFI). Based on Advanced Micro- wave Scanning Radiometer-Earth Observing System (AMSR-E) observations from June 1 to 16, 2011, RFI over Europe was identified and analyzed using the modified principal component analysis algorithm in this paper. The X band AMSR-E measurements in England and Italy are mostly affected by the stable, persistent, active microwave transmitters on the surface, while the RFI source of other European countries is the interference of the reflected geostationary TV satellite downlink signals to the measurements of spacebome microwave radiometers. The locations and intensities of the RFI induced by the geostationary TV and communication satellites changed with time within the observed period. The observations of spacebome microwave radiometers in ascending portions of orbits are usually interfered with over European land, while no RFI was detected in descending passes. The RFI locations and intensities from the reflection of downlink radiation are highly dependent upon the relative geometry between the geostationary satellite and the measuring passive sensor. Only these fields of view of a spaceborne instrument whose scan azimuths are close to the azimuth relative to the geostationary satellite are likely to be affected by RFI.
文摘Some typical samples are used to explore the quantitative correlation with their features between a convective cloud and its rainfall field,with which to develop two morphological functions for the correlation and by singling out their most suitable groups of parameters we propose a model for quantitatively estimating precipitation in the context o{ the in-advance recognition of meso-α convective system properties and its precipitating center.From the model fitting precision and forecasting accuracy we find that it is feasible to utilize geostationary meteorological satellite (GMS) digitalized imagery for estimating short-term rainfall in a quantitative manner.Also,evidence suggests that the model is supposed to be restricted in its applicability due to the fact that the employed samples are from rather typical rainfall events that are large-scale,slow-moving and have well-defined genesis and dissipative stages.
基金The CMA and JTWC best track archives were obtained from Typhoon Online website and NDBC website respectively.The real-time archives of ARCHER and ADT were downloaded from SSEC.WISC website.This study was supported by the Key Projects of the National Key R&D Program(No.2018YFC1506300)the National Basic Research Program of China(No.2015CB452806)+2 种基金the Key Program for International S&T Cooperation Projects of China(No.2017YFE0107700)the Natural Science Foundation of Shanghai(No.15ZR1449900)the National Natural Science Foundation of China(Nos.41675116,41575046,41775065,and 41405060).
文摘A spiral cloud belt matching(SCBeM)technique is proposed for automatically locating the tropical cyclone(TC)center position on the basis of multi-band geo-satellite images.The technique comprises four steps:fusion of multi-band geo-satellite images,extraction of TC cloud systems,construction of a spiral cloud belt template(CBT),and template matching to locate the TC center.In testing of the proposed SCBeM technique on 97 TCs over the western North Pacific during 2012-2015,the median error(ME)was 50 km.An independent test of another 29 TCs in 2016 resulted in a ME of 54 km.The SCBeM performs better for TCs with intensity above“typhoon”level than it does for weaker systems,and is not suitable for use on high-latitude or landfall TCs if their cloud band formations have been destroyed by westerlies or by terrain.The proposed SCBeM technique provides an additional solution for automatically and objectively locating the TC center and has the potential to be applied conveniently in an operational setting.Intercomparisons between the Automated Rotational Center Hurricane Eye Retrieval(ARCHER)and SCBeM methods using events from 2014 to 2016 reveal that ARCHER has better location accuracy.However,when IR imagery alone is used,the ME of SCBeM is 54 km,and in the case of low latitudes and low vertical wind shear the ME is 45-47 km,which approaches that of ARCHER(49 km).Thus,the SCBeM method is simple,has good time resolution,performs well and is a better choice for those TC operational agencies in the case that the microwave images,ASCAT,or other observations are unavailable.
基金supported in part by the National Natural Science Foundation of China under Grants 42192581,42090012,and 42071308in part by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)under Grant 2019QZKK0206in part by the open fund of Beijing Engineering Research Center for Global Land Remote Sensing Products.
文摘This paper extends a new temperature and emissivity separation(TES)algorithm for retrieving land surface temperature and emissivity(LST and LSE)to the Advanced Geosynchronous Radiation Imager(AGRI)onboard Fengyun-4A,China’s newest geostationary meteorological satellite.The extended TES algorithm was named the AGRI TES algorithm.The AGRI TES algorithm employs a modified water vapor scaling(WVS)method and a recalibrated empirical function over vegetated surfaces.In situ validation and cross-validation are utilized to investigate the accuracy of the retrieved LST and LSE.LST validation using the collected field measurements showed that the mean bias and RMSE of AGRI TES LST are 0.58 and 2.93 K in the daytime and−0.30 K and 2.18 K at nighttime,respectively;the AGRI official LST is systematically underestimated.Compared with the MODIS LST and LSE products(MYD21),the average bias and RMSE of AGRI TES LST are−0.26 K and 1.65 K,respectively.The AGRI TES LSE outperforms the AGRI official LSE in terms of accuracy and spatial integrity.This study demonstrates the good performance of the AGRI TES algorithm for the retrieval of high-quality LST and LSE,and the potential of the AGRI TES algorithm in producing operational LST and LSE products.
基金This work was supported by the National Natural Science Foundation of China(Project No.49794030)
文摘By use of GMS-4 infrared brightness temperature and visible albedo data from January to February in 1995,the method for extracting of sea ice parameters is developed.The digital remote sensing picture is obtained on Liaodong Bay.Based on the difference in physical properties between ice and water,a criterion distinguishing ice from water is set up.Ice thickness has been calculated according to the relationship between ice thickness and brightness as well as albedo.Ice concentration is retrieved due to the difference on albedo between ice and water.The results indicate that the accuracy of ice-water distinguishing is 84.8%,the errors of ice thickness and ice concentration are 3.8 cm and 22%,respectively.
基金National Natural Science Foundation of China(No.49794030 & 40105001).
文摘To study the possibility of improving the precision of retrieving precipitation through GMS-5 infrared data,the relationship between the data of GMS-5 infrared channel 1(IR1)and precipitation sounded by TRMM/PR was carefully studied through some cases gathered during the HUBEX 1998.First of all,the relationship between the brightness temperature(Tb)and PR- sounded near-surface rainfall rate(NSRR)was studied.Then,as PR can sound the inner structure of rainfall area.a unique advantage of this new instrument,the relationship between Tb and PR-sounded rainfall rate in each layer was also studied.Still,as PR can tell the rain type, those relationships were studied again according to the different types of precipitation(i.e. convective and stratiform).After comparing these outcomes with those from other references,it can be concluded that the relationship between Tb and PR-sounded rainfall rate is acceptable and it is possible to calibrate precipitation retrieved through Tb by PR data.
基金Supported by the National Key Research and Development Program of China (2018YFC1507004)。
文摘Geostationary Operational Environmental Satellite-16(GOES-16) Advanced Baseline Imager(ABI) observations of brightness temperature(TB) are used to examine the temporal evolutions of convection-affected structures of Hurricane Irma(2017) during its rapid intensification(RI) period from 0600 to 1800 UTC 4 September 2017.The ABI observations reveal that both an elliptical eye and a spiral rainband that originated from Irma's eyewall obviously exhibit wavenumber-2 TB asymmetries.The elliptical eye underwent a counterclockwise rotation at a mean speed of a wavenumber-2 vortex Rossby edge wave from 0815 to 1005 UTC 4 September.In the following about 2 hours(1025–1255 UTC 4 September),an inner spiral rainband originated from the eyewall and propagated at a phase speed that approximates the vortex Rossby wave(VRW) phase speed calculated from the aircraft reconnaissance data.During the RI period of Irma,ABI TB observations show an on–off occurrence of low TB intrusions into the eye,accompanying a phase lock of eyewall TB asymmetries of wavenumbers 1 and 2 and an outward propagation of VRW-like inner spiral rainbands from the eyewall.The phase lock leads to an energy growth of Irma's eyewall asymmetries.Although the eye remained clear from 1415 to 1725 UTC 4 September,an inner spiral rainband that originated from a large convective area also had a VRW-like outward propagation,which is probably due to a vertical tilt of Irma.This study suggests a potential link between convection sensitive GOES imager observations and hurricane dynamics.