The two vegetation transfer parameters ofτ(Vegetation Optical Depth,VOD)andω(Omega)could vary significantly across microwave channels in terms of frequencies,polarizations,and incidence angles,and their channel-depe...The two vegetation transfer parameters ofτ(Vegetation Optical Depth,VOD)andω(Omega)could vary significantly across microwave channels in terms of frequencies,polarizations,and incidence angles,and their channel-dependent characteristics have not yet been fully investigated.In this study,we investigate the channel dependence of vegetation effects on microwave emissions from soils using a higher-order vegetation radiative transfer model of Tor Vergata.Corn was selected as the subject of investigation,and a corn growth model was developed utilizing field data collected from the multifrequency and multi-angular ground-based microwave radiation experiment from the Soil Moisture Experiment in the Luan River(SMELR).Upon compilation of the simulation dataset of microwave emissions of the corn field,the effective scattering albedo across different channels were calculated using the Tor Vergata model.Results show that vertical polarization of the vegetation optical depth is more affected by incidence angle changes,while horizontal polarization exhibits lower variations in vegetation optical depth due to incidence angle adjustments.The channel dependence of vegetation optical depth can be described as the polarization dependence parameter(CP)and the frequency dependence parameter(Cf).These two parameters enable the calculation of vegetation optical depth at any channel under three adjacent frequencies(L-band,C-band and X-band).The effective scattering albedo of vegetation does not vary significantly with vegetation height or angle.It primarily depends on frequency and polarization,showing an overall increasing trend with increasing frequency.The effective scattering albedo with vertical polarization is slightly higher than that with horizontal polarization at higher frequencies,while both are lower in the L-band.This investigation is helpful for understanding the vegetation effects on microwave emissions from soils,ultimately advancing the accuracy of large-scale soil moisture retrieval in vegetated areas.展开更多
Assessing plant water status is important for monitoring plant physiology. Previous studies showed that radio waves are attenuated when passing through vegetation such as trees. The degree of radio frequency (RF) loss...Assessing plant water status is important for monitoring plant physiology. Previous studies showed that radio waves are attenuated when passing through vegetation such as trees. The degree of radio frequency (RF) loss has previously been measured for various tree types but the relationship between water content and RF loss has not been quantified. In this study, the amount of water inside leaves was expressed as an effective water path (EWP), the thickness of a hypothetical sheet of 100% water with the same mass. A 2.4331 GHz radio wave was transmitted through a wooden frame covered on both sides with 5 mm clear acrylic sheets and filled with <em>Eucalyptus laevopinea</em> leaves. The RF loss through the leaves was measured for different stages of drying. The results showed that there is a nonlinear relationship between effective water path (EWP) in mm and RF loss in dB. It can be concluded that 2.4 GHz frequency radio waves can be used to predict the water content inside eucalyptus leaves (0 < EWP < 14 mm;RMSE ± 0.87 mm) and demonstrates the potential to measure the water content of whole trees.展开更多
Over the past 4 decades,Southwest China has the fast vegetation growth and aboveground biomass carbon(AGC)accumulation,largely attributed to the active implementation of ecological projects.However,Southwest China has...Over the past 4 decades,Southwest China has the fast vegetation growth and aboveground biomass carbon(AGC)accumulation,largely attributed to the active implementation of ecological projects.However,Southwest China has been threatened by frequent extreme drought events recently,potentially countering the expected large AGC increase caused by the ecological projects.Here,we used the L-band vegetation optical depth to quantify the AGC dynamics over Southwest China during the period 2013-2021.Our results showed a net AGC sink of 0.064[0.057,0.077]Pg C year^(−1)(the range represents the maximum and minimum AGC values),suggesting that Southwest China acted as an AGC sink over the study period.Note that the AGC loss of 0.113[0.101,0.136]Pg C year^(−1)was found during 2013-2014,which could mainly be attributed to the negative influence of extreme droughts on AGC changes in Southwest China,particularly in the Yunnan province.For each land use type(i.e.,dense forests,persistent forests,nonforests,afforestation,and forestry),the largest AGC stock increase of 0.032[0.028,0.036]Pg C year^(−1)was found in nonforests,owing to their widespread land cover rate over Southwest China.For AGC density(i.e.,AGC per unit area),the afforestation areas showed the largest AGC density increase of 0.808[0.724,0.985]Mg C ha−1 year^(−1),reflecting the positive effect of afforestation on AGC increase.Moreover,the karst areas exhibited a higher increasing rate of AGC density than nonkarst areas,suggesting that the karst ecosystems have a high carbon sink capacity over Southwest China.展开更多
基金supported by National Natural Science Foundation of China(grant number 42090014)National Key Research and Development Program of China(grant number 2021YFB3900104)the Dragon 5 Cooperation Programme(grant number 59312).
文摘The two vegetation transfer parameters ofτ(Vegetation Optical Depth,VOD)andω(Omega)could vary significantly across microwave channels in terms of frequencies,polarizations,and incidence angles,and their channel-dependent characteristics have not yet been fully investigated.In this study,we investigate the channel dependence of vegetation effects on microwave emissions from soils using a higher-order vegetation radiative transfer model of Tor Vergata.Corn was selected as the subject of investigation,and a corn growth model was developed utilizing field data collected from the multifrequency and multi-angular ground-based microwave radiation experiment from the Soil Moisture Experiment in the Luan River(SMELR).Upon compilation of the simulation dataset of microwave emissions of the corn field,the effective scattering albedo across different channels were calculated using the Tor Vergata model.Results show that vertical polarization of the vegetation optical depth is more affected by incidence angle changes,while horizontal polarization exhibits lower variations in vegetation optical depth due to incidence angle adjustments.The channel dependence of vegetation optical depth can be described as the polarization dependence parameter(CP)and the frequency dependence parameter(Cf).These two parameters enable the calculation of vegetation optical depth at any channel under three adjacent frequencies(L-band,C-band and X-band).The effective scattering albedo of vegetation does not vary significantly with vegetation height or angle.It primarily depends on frequency and polarization,showing an overall increasing trend with increasing frequency.The effective scattering albedo with vertical polarization is slightly higher than that with horizontal polarization at higher frequencies,while both are lower in the L-band.This investigation is helpful for understanding the vegetation effects on microwave emissions from soils,ultimately advancing the accuracy of large-scale soil moisture retrieval in vegetated areas.
文摘Assessing plant water status is important for monitoring plant physiology. Previous studies showed that radio waves are attenuated when passing through vegetation such as trees. The degree of radio frequency (RF) loss has previously been measured for various tree types but the relationship between water content and RF loss has not been quantified. In this study, the amount of water inside leaves was expressed as an effective water path (EWP), the thickness of a hypothetical sheet of 100% water with the same mass. A 2.4331 GHz radio wave was transmitted through a wooden frame covered on both sides with 5 mm clear acrylic sheets and filled with <em>Eucalyptus laevopinea</em> leaves. The RF loss through the leaves was measured for different stages of drying. The results showed that there is a nonlinear relationship between effective water path (EWP) in mm and RF loss in dB. It can be concluded that 2.4 GHz frequency radio waves can be used to predict the water content inside eucalyptus leaves (0 < EWP < 14 mm;RMSE ± 0.87 mm) and demonstrates the potential to measure the water content of whole trees.
基金supported in part by research grants from the National Natural Science Foundation of China(Grant Nos.42322103,42171339,and 41830648).
文摘Over the past 4 decades,Southwest China has the fast vegetation growth and aboveground biomass carbon(AGC)accumulation,largely attributed to the active implementation of ecological projects.However,Southwest China has been threatened by frequent extreme drought events recently,potentially countering the expected large AGC increase caused by the ecological projects.Here,we used the L-band vegetation optical depth to quantify the AGC dynamics over Southwest China during the period 2013-2021.Our results showed a net AGC sink of 0.064[0.057,0.077]Pg C year^(−1)(the range represents the maximum and minimum AGC values),suggesting that Southwest China acted as an AGC sink over the study period.Note that the AGC loss of 0.113[0.101,0.136]Pg C year^(−1)was found during 2013-2014,which could mainly be attributed to the negative influence of extreme droughts on AGC changes in Southwest China,particularly in the Yunnan province.For each land use type(i.e.,dense forests,persistent forests,nonforests,afforestation,and forestry),the largest AGC stock increase of 0.032[0.028,0.036]Pg C year^(−1)was found in nonforests,owing to their widespread land cover rate over Southwest China.For AGC density(i.e.,AGC per unit area),the afforestation areas showed the largest AGC density increase of 0.808[0.724,0.985]Mg C ha−1 year^(−1),reflecting the positive effect of afforestation on AGC increase.Moreover,the karst areas exhibited a higher increasing rate of AGC density than nonkarst areas,suggesting that the karst ecosystems have a high carbon sink capacity over Southwest China.
