Radiative transfer models have been widely used to simulate the radar backscattering from forested areas.A three-dimensional radar backscatter model of forest canopy developed in previous studies takes full account of...Radiative transfer models have been widely used to simulate the radar backscattering from forested areas.A three-dimensional radar backscatter model of forest canopy developed in previous studies takes full account of spatial position of trees in a forest stand,and the interactions among crown,trunk and ground surface.The model predicted well for the co-polarized backscatter measurements,but underestimated the backscattering for cross-polarization,primarily because only the first-order scattering within tree crowns was considered in the model.The backscattering at cross-polarization depends strongly on multiple scatter-ing within tree crowns.To produce good estimations for cross-polarized component,the matrix-doubling method is employed here to compute multiple-scattering within the crown.The modified model is compared with the original model,and the field forest measurements and AIRSAR data are used for validation of the modified model.The cross-polarization backscattering is improved in different degrees for different crown structures and at different bands.展开更多
A P-band polarimetric synthetic aperture radar(PolSAR)sensor has deep penetration ability into and through the vegetation canopies in forested environments.Thus,the sensor is of great potential to accurately assess fo...A P-band polarimetric synthetic aperture radar(PolSAR)sensor has deep penetration ability into and through the vegetation canopies in forested environments.Thus,the sensor is of great potential to accurately assess forest parameters such as coverage,stand density,and tree height.Unfortunately,the radar backscatter from complex terrain can adversely impact the backscatter from trees or forests,and forest parameters assessed can be erroneous.Thus,reducing the topographic impact is an urgent must.In this study,a topographic compensation algorithm has been studied.To assess the algorithm’s validity and effectiveness,we applied it to P-band PolSAR datasets in four forested areas in the US.Trees in the forest stands have diverse species,and the topographic conditions of the terrain differ.Significant topographic impact on the P-band PolSAR data exists before the topographic compensation algorithm.After the algorithm,the impact decreases noticeably qualitatively and quantitatively.The algorithm is valid and effective in reducing the topographic influence on the PolSAR data and,consequently,provides a better chance of retrieving accurate forest parameters.展开更多
Because of the cloudy conditions during the rice growth period,rice is one of the agri-cultural crops most suited to monitoring with the SAR instruments.Backscatter response measured by SAR is correlated with rice con...Because of the cloudy conditions during the rice growth period,rice is one of the agri-cultural crops most suited to monitoring with the SAR instruments.Backscatter response measured by SAR is correlated with rice conditions,including height,density,biomass and structure,which are variable at different growing stages.In this paper,multi-date ENVISAT ASAR Alternating Polarization Mode(APMode)imageries were acquired during the rice crop growing cycle.At the same time,the rice parameters were measured in field.A continuous canopy model was used to compute the back-scattering from rice fields during the growth cycle,and the relationship between rice parameters and radar backscattering coefficients from both ASAR and modeling was analyzed.The effects of polari-zation,incidence angle and polarization on radar backscattering coefficients were analyzed.It was found that simulated radar backscatter has similar trends as ASAR data.This will be meaningful for the further research of rice parameters estimation from ASAR data.Different features show signifi-cantly different signatures in ASAR images and they follow some certain laws,so rice area can be accurately mapped by using multi-temporal SAR images,then rice yield can be estimated.展开更多
基金supported by National Basic Research Program of China(Grant No.2007CB714404)Hi-tech Research and Development Program of China(Grant No.2006AA12Z114)National Natural Science Foundation of China(Grant Nos.40701124,40734025)
文摘Radiative transfer models have been widely used to simulate the radar backscattering from forested areas.A three-dimensional radar backscatter model of forest canopy developed in previous studies takes full account of spatial position of trees in a forest stand,and the interactions among crown,trunk and ground surface.The model predicted well for the co-polarized backscatter measurements,but underestimated the backscattering for cross-polarization,primarily because only the first-order scattering within tree crowns was considered in the model.The backscattering at cross-polarization depends strongly on multiple scatter-ing within tree crowns.To produce good estimations for cross-polarized component,the matrix-doubling method is employed here to compute multiple-scattering within the crown.The modified model is compared with the original model,and the field forest measurements and AIRSAR data are used for validation of the modified model.The cross-polarization backscattering is improved in different degrees for different crown structures and at different bands.
基金supported by the National Natural Science Foundation of China under Grants No.41771401 and No.42350710201.
文摘A P-band polarimetric synthetic aperture radar(PolSAR)sensor has deep penetration ability into and through the vegetation canopies in forested environments.Thus,the sensor is of great potential to accurately assess forest parameters such as coverage,stand density,and tree height.Unfortunately,the radar backscatter from complex terrain can adversely impact the backscatter from trees or forests,and forest parameters assessed can be erroneous.Thus,reducing the topographic impact is an urgent must.In this study,a topographic compensation algorithm has been studied.To assess the algorithm’s validity and effectiveness,we applied it to P-band PolSAR datasets in four forested areas in the US.Trees in the forest stands have diverse species,and the topographic conditions of the terrain differ.Significant topographic impact on the P-band PolSAR data exists before the topographic compensation algorithm.After the algorithm,the impact decreases noticeably qualitatively and quantitatively.The algorithm is valid and effective in reducing the topographic influence on the PolSAR data and,consequently,provides a better chance of retrieving accurate forest parameters.
基金This work was supported by the National Natural Science Foundation of China(Grant No.40171070)the Knowledge Innovation Project of the Chinese Academy of Sciences(Grant No.CX010014).We would like to thank European Space Agency for providing ENVISAT ASAR data,and the Chinese Academy of Sciences and the Chinese Academy of Forestry for field data collection and data analysis.
文摘Because of the cloudy conditions during the rice growth period,rice is one of the agri-cultural crops most suited to monitoring with the SAR instruments.Backscatter response measured by SAR is correlated with rice conditions,including height,density,biomass and structure,which are variable at different growing stages.In this paper,multi-date ENVISAT ASAR Alternating Polarization Mode(APMode)imageries were acquired during the rice crop growing cycle.At the same time,the rice parameters were measured in field.A continuous canopy model was used to compute the back-scattering from rice fields during the growth cycle,and the relationship between rice parameters and radar backscattering coefficients from both ASAR and modeling was analyzed.The effects of polari-zation,incidence angle and polarization on radar backscattering coefficients were analyzed.It was found that simulated radar backscatter has similar trends as ASAR data.This will be meaningful for the further research of rice parameters estimation from ASAR data.Different features show signifi-cantly different signatures in ASAR images and they follow some certain laws,so rice area can be accurately mapped by using multi-temporal SAR images,then rice yield can be estimated.
