The flow over mountain is quite complicated. There are a lot of papers on this problem and a lot of progresses have been made. However, in the most of these papers, just the dynamics contributions of mountain have bee...The flow over mountain is quite complicated. There are a lot of papers on this problem and a lot of progresses have been made. However, in the most of these papers, just the dynamics contributions of mountain have been analysed; the effect of the friction is often neglected. Since the frictional effect is always associated with flow, especially when it flows over the mountain. The study shows that the friction is small in the magnitude but it is not a negligible effect because it changes the features of the flow. In the case of super-or sub-critical flow, there are two extremes: one maximum, one minimum of the fluid surface on the lee-side of the mountain, while in the inviscid fluid, there is just one extreme. The frictional effect should neither be too strong nor too weak to make the situation happened according to the investigation of this paper.展开更多
Land surface temperature(LST) is a key parameter reflecting the interaction between land and atmosphere. Currently,thermal infrared(TIR) quantitative remote sensing technology is the only means to obtain large-scale, ...Land surface temperature(LST) is a key parameter reflecting the interaction between land and atmosphere. Currently,thermal infrared(TIR) quantitative remote sensing technology is the only means to obtain large-scale, high spatial resolution LST. Accurately retrieving high spatial resolution mountainous LST(MLST) plays an important role in the study of mountain climate change. The complex terrain and strong spatial heterogeneity in mountainous areas change the geometric relationship between the surface and satellite sensors, affecting the radiation received by the sensors, and rendering the assumption of planar parallelism invalid. In this study, considering the influence of complex terrain in mountainous areas on atmospheric downward radiation and the thermal radiation contribution of adjacent pixels, a mountainous TIR radiative transfer model based on the sky view factor was developed. Combining with the atmospheric radiative transfer model MODTRAN 5.2, a nonlinear generalized split-window algorithm suitable for high spatial resolution MLST retrieval was constructed and applied to Landsat-9 TIRS-2satellite TIR remote sensing data. The analysis results indicate that neglecting the topographic and adjacency effects would lead to significant discrepancies in LST retrieval, with simulated data showing LST differences of up to 2.5 K. Furthermore, due to the lack of measured MLST in the field, the MLST accuracy obtained by this retrieval method was indirectly validated using the currently recognized highest-accuracy forward 3D radiative transfer model DART. The MLST and emissivity were input into the DART model to simulate the brightness temperature at the top of the atmosphere(TOA) of Landsat-9 band 10, and compared with the brightness temperature at TOA of Landsat-9 band 10. The RMSE(Root Mean Square Error) for the two subregions was0.50 and 0.61 K, respectively, indicating that the method proposed can retrieve high-precision MLST.展开更多
In mountainous surfaces,land surface temperature(LST)plays a vital role in surface energy budget and vegetation-soil ecosystems.Despite advancements in retrieving LST from thermal infrared measurements at various spat...In mountainous surfaces,land surface temperature(LST)plays a vital role in surface energy budget and vegetation-soil ecosystems.Despite advancements in retrieving LST from thermal infrared measurements at various spatial and temporal scales,accurately estimating LST for complex terrain remains challenging.This challenge arises from the conflict between the topographic effect and the assumption of flatten surface in many existing studies.In the absence of a simple and practical model for the topographic effect on the directional anisotropies of LST(LSTDA)over mountainous areas,the equivalent slope method is introduced to bridge the gap between studies conducted on flat surfaces and complex terrain.The proposed thermal equivalent slope kernel-driven(TESKD)model is validated using measurements and simulations from an unmanned aerial vehicle(UAV)system and a 3-dimensional raytracing model,respectively.Results indicate the following:(a)Under varying topographic conditions,vegetation cover,and solar zenith angles,there is a significant impact of topography on LSTDA.The average effect is greater than 0.5 K and can reach up to 1.5 K at the higher solar zenith angle(50°).(b)Based on UAV data,TESKD provides a better explanation and fitting effect for LSTDA in 3 typical mountainous surfaces including valley,peak,and solo-slope,with an average root mean square error(RMSE)of 0.27 K and an average coefficient of determinations of 0.628 of the 3 conditions,compared to a flat model(0.35 K and 0.335).(c)Based on simulations,TESKD exhibits more than a 30%improvement in accuracy,and for sparsely vegetated surfaces,the difference in RMSE can be up to 0.8 K when considering the topographic effect compared to not considering it.The new model can help to understand the radiative transfer process in heterogeneous mountainous surfaces and serves as a valuable tool for studies associated with water and carbon cycles.展开更多
基金This work was supported by the National Science Foundation of U.S.A.National Natural Science Foundation of China.
文摘The flow over mountain is quite complicated. There are a lot of papers on this problem and a lot of progresses have been made. However, in the most of these papers, just the dynamics contributions of mountain have been analysed; the effect of the friction is often neglected. Since the frictional effect is always associated with flow, especially when it flows over the mountain. The study shows that the friction is small in the magnitude but it is not a negligible effect because it changes the features of the flow. In the case of super-or sub-critical flow, there are two extremes: one maximum, one minimum of the fluid surface on the lee-side of the mountain, while in the inviscid fluid, there is just one extreme. The frictional effect should neither be too strong nor too weak to make the situation happened according to the investigation of this paper.
基金supported by the National Natural Science Foundation of China (Grant No. 42230109)the Yunling Scholar Project of the “Xingdian Talent Support Program” of Yunnan Province (Grant No. 202221002)+1 种基金the Platform Construction Project of High-Level Talent in the Kunming University of Science and Technology (KUST) (Grant No. 7202221001)the “Top Innovative Talent” Program for Doctoral Candidates in the KUST (Grant No. CA24163M078A)。
文摘Land surface temperature(LST) is a key parameter reflecting the interaction between land and atmosphere. Currently,thermal infrared(TIR) quantitative remote sensing technology is the only means to obtain large-scale, high spatial resolution LST. Accurately retrieving high spatial resolution mountainous LST(MLST) plays an important role in the study of mountain climate change. The complex terrain and strong spatial heterogeneity in mountainous areas change the geometric relationship between the surface and satellite sensors, affecting the radiation received by the sensors, and rendering the assumption of planar parallelism invalid. In this study, considering the influence of complex terrain in mountainous areas on atmospheric downward radiation and the thermal radiation contribution of adjacent pixels, a mountainous TIR radiative transfer model based on the sky view factor was developed. Combining with the atmospheric radiative transfer model MODTRAN 5.2, a nonlinear generalized split-window algorithm suitable for high spatial resolution MLST retrieval was constructed and applied to Landsat-9 TIRS-2satellite TIR remote sensing data. The analysis results indicate that neglecting the topographic and adjacency effects would lead to significant discrepancies in LST retrieval, with simulated data showing LST differences of up to 2.5 K. Furthermore, due to the lack of measured MLST in the field, the MLST accuracy obtained by this retrieval method was indirectly validated using the currently recognized highest-accuracy forward 3D radiative transfer model DART. The MLST and emissivity were input into the DART model to simulate the brightness temperature at the top of the atmosphere(TOA) of Landsat-9 band 10, and compared with the brightness temperature at TOA of Landsat-9 band 10. The RMSE(Root Mean Square Error) for the two subregions was0.50 and 0.61 K, respectively, indicating that the method proposed can retrieve high-precision MLST.
基金supported in part by the Chinese Natural Science Foundation Project(42130111,42271362,2020YFA0608703,and 41930111).
文摘In mountainous surfaces,land surface temperature(LST)plays a vital role in surface energy budget and vegetation-soil ecosystems.Despite advancements in retrieving LST from thermal infrared measurements at various spatial and temporal scales,accurately estimating LST for complex terrain remains challenging.This challenge arises from the conflict between the topographic effect and the assumption of flatten surface in many existing studies.In the absence of a simple and practical model for the topographic effect on the directional anisotropies of LST(LSTDA)over mountainous areas,the equivalent slope method is introduced to bridge the gap between studies conducted on flat surfaces and complex terrain.The proposed thermal equivalent slope kernel-driven(TESKD)model is validated using measurements and simulations from an unmanned aerial vehicle(UAV)system and a 3-dimensional raytracing model,respectively.Results indicate the following:(a)Under varying topographic conditions,vegetation cover,and solar zenith angles,there is a significant impact of topography on LSTDA.The average effect is greater than 0.5 K and can reach up to 1.5 K at the higher solar zenith angle(50°).(b)Based on UAV data,TESKD provides a better explanation and fitting effect for LSTDA in 3 typical mountainous surfaces including valley,peak,and solo-slope,with an average root mean square error(RMSE)of 0.27 K and an average coefficient of determinations of 0.628 of the 3 conditions,compared to a flat model(0.35 K and 0.335).(c)Based on simulations,TESKD exhibits more than a 30%improvement in accuracy,and for sparsely vegetated surfaces,the difference in RMSE can be up to 0.8 K when considering the topographic effect compared to not considering it.The new model can help to understand the radiative transfer process in heterogeneous mountainous surfaces and serves as a valuable tool for studies associated with water and carbon cycles.
