The objective of this study is to improve the performance of semi-empirical radar backscatter models, which are mainly used in microwave remote sensing (Oh 1992, Oh 2004 and Dubois). The study is based on satellite an...The objective of this study is to improve the performance of semi-empirical radar backscatter models, which are mainly used in microwave remote sensing (Oh 1992, Oh 2004 and Dubois). The study is based on satellite and ground data collected on bare soil surfaces during the Multispectral Crop Monitoring experimental campaign of the CESBIO laboratory in 2010 over an agricultural region in southwestern France. The dataset covers a wide range of soil (viewing top soil moisture, surface roughness and texture) and satellite (at different frequencies: X-, C- and L-bands, and different incidence angles: 24.3° to 53.3°) configurations. The proposed methodology consists in identifying and correcting the residues of the models, depending on the surface properties (roughness, moisture, texture) and/or sensor characteristics (frequency, incidence angle). Finally, one model has been retained for each frequency domain. Results show that the enhancements of the models significantly increase the simulation performances. The coefficient of correlation increases of 23% in mean and the simulation errors (RMSE) are reduced to below 2 dB (at the X and C-bands) and to 1 dB at the L-band, compared to the initial models. At the X- and C-bands, the best performances of the modified models are provided by Dubois, whereas Oh 2004 is more suitable for the L-band (r is equal to 0.69, 0.65 and 0.85). Moreover, the modified models of Oh 1992 and 2004 and Dubois, developed in this study, offer a wider domain of validity than the initial formalism and increase the capabilities of retrieving the backscattering signal in view of applications of such approaches to stronglycontrasted agricultural surface states.展开更多
In order to predict the bottom backscattering strength more accurately, the stratified structure of the seafloor is considered. The seafloor is viewed as an elastic half-space basement covered by a fluid sediment laye...In order to predict the bottom backscattering strength more accurately, the stratified structure of the seafloor is considered. The seafloor is viewed as an elastic half-space basement covered by a fluid sediment layer with finite thickness. On the basis of calculating acoustic field in the water, the sediment layer, and the basement, four kinds of scattering mechanisms are taken into account, including roughness scattering from the water-sediment interface, volume scattering from the sediment layer, roughness scattering from the sediment-basement interface,and volume scattering from the basement. Then a backscattering model for a stratified seafloor applying to low frequency（0.1-10 kHz） is established. The simulation results show that the roughness scattering from the sediment-basement interface and the volume scattering from the basement are more prominent at relative low frequency（below 1.0 kHz）. While with the increase of the frequency, the contribution of them to total bottom scattering gradually becomes weak. And the results ultimately approach to the predictions of the high-frequency（10-100 kHz） bottom scattering model. When the sound speed and attenuation of the shear wave in the basement gradually decrease, the prediction of the model tends to that of the full fluid model, which validates the backscattering model for the stratified seafloor in another aspect.展开更多
Rain is one of the main sources of error in dual-frequency altimeter Jason-1 wind measurement. In this study, a new radar altimeter backscatter model is proposed and validated to eliminate rain effects. The model take...Rain is one of the main sources of error in dual-frequency altimeter Jason-1 wind measurement. In this study, a new radar altimeter backscatter model is proposed and validated to eliminate rain effects. The model takes into account attenuation, volume backscattering, and sea surface perturbation by raindrops under rain conditions. A match-up dataset is built to evaluate rain effects, in combination with the Jason-1 normalized radar cross section, precipitation radar data from the Tropical Rainfall Measuring Mission, and sea surface wind reanalysis data from the European Centre for Medium-Range Weather Forecasts. The results show that rain-induced surface perturbation backscatter increases with rain rate at Ku-band, but their correlation at C-band is poor. In addition, rain surface perturbation and attenuation have major effects on radar altimeter wind measurements. Finally, a rain correction model for Jason-1 winds is developed and validation results prove its ability to reduce rain-induced inaccuracies in wind retrievals.展开更多
In this paper,research is conducted on the characteristics of coda Q values of the Jiangsu area,based on the Aki single backscattering model with the waveforms recorded by the Jiangsu digital seismic network. The resu...In this paper,research is conducted on the characteristics of coda Q values of the Jiangsu area,based on the Aki single backscattering model with the waveforms recorded by the Jiangsu digital seismic network. The results show that the Jiangsu area is a high Q value area as a whole,but the Q value differs obviously between different regions,characterized generally as high in the south and low in the north. This study focuses on 4 sub-regions where the stations are relatively dense,the tectonic features are distinguishing,and the calculation results of coda Q0 are fairly concentrated,and obtains the characteristic relationship between the Q value and frequency of the 4 regions. The region from south Jiangsu to the Yangtze River estuary and that around the Maoshan fault zone are the high Q value areas in Jiangsu; the region from central Jiangsu to the waterfront area is the low Q value area in Jiangsu Province,and the Lianyungang region in northern Jiangsu is the moderate Q value area. Comparing the tectonic activity and seismicity of the 4 different Q value sub-regions,there is a certain correlation between Q value,crustal movement and seismicity.展开更多
A backscatter model was developed for measur-ing wind field with the far-field approximation method.The theoretical computation and computer simulations with one spatial dimension show that this model can realisticall...A backscatter model was developed for measur-ing wind field with the far-field approximation method.The theoretical computation and computer simulations with one spatial dimension show that this model can realistically describe the physical meaning and process of the three methods in wind measurements including the spaced antenna(SA)method,Doppler beam swing(DBS)method,and spaced interferometry(SI).The computational difficulties of the traditional theoretical model cannot only be smoothed away,but common characteristics and differences of the three methods can be compared deeply.The comparison of the numerical results between the Wuhan medium frequency(MF)radar(30°N,114°E)observation and the computer simulation of the full correlation analysis(FCA)of the SA method indicates that the two results agree very well and this model has practical application.展开更多
文摘The objective of this study is to improve the performance of semi-empirical radar backscatter models, which are mainly used in microwave remote sensing (Oh 1992, Oh 2004 and Dubois). The study is based on satellite and ground data collected on bare soil surfaces during the Multispectral Crop Monitoring experimental campaign of the CESBIO laboratory in 2010 over an agricultural region in southwestern France. The dataset covers a wide range of soil (viewing top soil moisture, surface roughness and texture) and satellite (at different frequencies: X-, C- and L-bands, and different incidence angles: 24.3° to 53.3°) configurations. The proposed methodology consists in identifying and correcting the residues of the models, depending on the surface properties (roughness, moisture, texture) and/or sensor characteristics (frequency, incidence angle). Finally, one model has been retained for each frequency domain. Results show that the enhancements of the models significantly increase the simulation performances. The coefficient of correlation increases of 23% in mean and the simulation errors (RMSE) are reduced to below 2 dB (at the X and C-bands) and to 1 dB at the L-band, compared to the initial models. At the X- and C-bands, the best performances of the modified models are provided by Dubois, whereas Oh 2004 is more suitable for the L-band (r is equal to 0.69, 0.65 and 0.85). Moreover, the modified models of Oh 1992 and 2004 and Dubois, developed in this study, offer a wider domain of validity than the initial formalism and increase the capabilities of retrieving the backscattering signal in view of applications of such approaches to stronglycontrasted agricultural surface states.
基金The National Natural Science Foundation of China under contract Nos 41606081,41330965 and 41527809the Taishan Scholar Project Funding under contract No.tspd20161007
文摘In order to predict the bottom backscattering strength more accurately, the stratified structure of the seafloor is considered. The seafloor is viewed as an elastic half-space basement covered by a fluid sediment layer with finite thickness. On the basis of calculating acoustic field in the water, the sediment layer, and the basement, four kinds of scattering mechanisms are taken into account, including roughness scattering from the water-sediment interface, volume scattering from the sediment layer, roughness scattering from the sediment-basement interface,and volume scattering from the basement. Then a backscattering model for a stratified seafloor applying to low frequency（0.1-10 kHz） is established. The simulation results show that the roughness scattering from the sediment-basement interface and the volume scattering from the basement are more prominent at relative low frequency（below 1.0 kHz）. While with the increase of the frequency, the contribution of them to total bottom scattering gradually becomes weak. And the results ultimately approach to the predictions of the high-frequency（10-100 kHz） bottom scattering model. When the sound speed and attenuation of the shear wave in the basement gradually decrease, the prediction of the model tends to that of the full fluid model, which validates the backscattering model for the stratified seafloor in another aspect.
基金Supported by the Knowledge Innovation Program of Chinese Academy of Sciences (No.Y0S04300KB)the Major Program for the Research Equipment of Chinese Academy of Sciences (No.YZ200946)
文摘Rain is one of the main sources of error in dual-frequency altimeter Jason-1 wind measurement. In this study, a new radar altimeter backscatter model is proposed and validated to eliminate rain effects. The model takes into account attenuation, volume backscattering, and sea surface perturbation by raindrops under rain conditions. A match-up dataset is built to evaluate rain effects, in combination with the Jason-1 normalized radar cross section, precipitation radar data from the Tropical Rainfall Measuring Mission, and sea surface wind reanalysis data from the European Centre for Medium-Range Weather Forecasts. The results show that rain-induced surface perturbation backscatter increases with rain rate at Ku-band, but their correlation at C-band is poor. In addition, rain surface perturbation and attenuation have major effects on radar altimeter wind measurements. Finally, a rain correction model for Jason-1 winds is developed and validation results prove its ability to reduce rain-induced inaccuracies in wind retrievals.
基金jointly funded by the Science & Technology Pillar Program of Jiangsu Province(BE2011814)the Youth Research Project on Earthquake Trend Tracking of China Earthquake Administration(2014020122)the Key Project of Youth Fund of Earthquake Administration of Jiangsu Province(201402)
文摘In this paper,research is conducted on the characteristics of coda Q values of the Jiangsu area,based on the Aki single backscattering model with the waveforms recorded by the Jiangsu digital seismic network. The results show that the Jiangsu area is a high Q value area as a whole,but the Q value differs obviously between different regions,characterized generally as high in the south and low in the north. This study focuses on 4 sub-regions where the stations are relatively dense,the tectonic features are distinguishing,and the calculation results of coda Q0 are fairly concentrated,and obtains the characteristic relationship between the Q value and frequency of the 4 regions. The region from south Jiangsu to the Yangtze River estuary and that around the Maoshan fault zone are the high Q value areas in Jiangsu; the region from central Jiangsu to the waterfront area is the low Q value area in Jiangsu Province,and the Lianyungang region in northern Jiangsu is the moderate Q value area. Comparing the tectonic activity and seismicity of the 4 different Q value sub-regions,there is a certain correlation between Q value,crustal movement and seismicity.
文摘A backscatter model was developed for measur-ing wind field with the far-field approximation method.The theoretical computation and computer simulations with one spatial dimension show that this model can realistically describe the physical meaning and process of the three methods in wind measurements including the spaced antenna(SA)method,Doppler beam swing(DBS)method,and spaced interferometry(SI).The computational difficulties of the traditional theoretical model cannot only be smoothed away,but common characteristics and differences of the three methods can be compared deeply.The comparison of the numerical results between the Wuhan medium frequency(MF)radar(30°N,114°E)observation and the computer simulation of the full correlation analysis(FCA)of the SA method indicates that the two results agree very well and this model has practical application.
