The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satell...The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satellite observations, the spatio-temporal characteristics of MILS_BRF data have rarely been explicitly and comprehensively analysed. Results from 5-yr(2011–2015) of MILS_BRF dataset from a typical region in central Northeast Asia as the study area showed that the monthly area coverage as well as MILS_BRF data quantity varies significantly, from the highest in October(99.05%) through median in June/July(78.09%/75.21%) to lowest in January(18.97%), and a large data-vacant area exists in the study area during four consecutive winter months(December through March). The data-vacant area is mainly composed of crop lands and cropland/natural vegetation mosaic. The amount of data within the principal plane(PP)±30°(nPP) or cross PP ±30°(nCP), varies intra-annually with significant differences from different view zeniths or forward/backward scattering directions. For example, multiple off-nadir cameras have nPP but no nCP data for up to six months(September through February), with the opposite occurring in June and July. This study provides explicit and comprehensive information about the spatio-temporal characteristics of product coverage and observation geometry of MILS_BRF in the study area. Results provide required user reference information for MILS_BRF to evaluate performance of BRDF models or to compare with other satellite-derived BRF or albedo products. Comparing this final product to on-satellite observations, what was found here reveals a new perspective on product spatial coverage and observation geometry for multi-angle remote sensing.展开更多
Lunar occultation observations are useful in refining lunar limb profiles, which will be used for the analysis of solar eclipse observations to detect the variation of the solar diameter, and in detecting the possible...Lunar occultation observations are useful in refining lunar limb profiles, which will be used for the analysis of solar eclipse observations to detect the variation of the solar diameter, and in detecting the possible errors of the Hipparcos proper motion system. Many lunar occultations have been observed in Japan. Some of the results are shown in this paper to encourage people in the world to observe more lunar occultations with better accuracies.展开更多
An extended-state-observer(ESO) based predictive control scheme is proposed for the autopilot of lunar landing.The slosh fuel masses exert forces and torques on the rigid body of lunar module(LM),such disturbances wil...An extended-state-observer(ESO) based predictive control scheme is proposed for the autopilot of lunar landing.The slosh fuel masses exert forces and torques on the rigid body of lunar module(LM),such disturbances will dramatically undermine the stability of autopilot system.The fuel sloshing dynamics and uncertainties due to the time-varying parameters are considered as a generalized disturbance which is estimated by an ESO from the measured attitude signals and the control input signals.Then a continuous-time predictive controller driven by the estimated states and disturbances is designed to obtain the virtual control input,which is allocated to the real control actuators according to a deadband logic.The 6-DOF simulation results reveal the effectiveness of the proposed method when dealing with the fuel sloshing dynamics and parameter perturbations.展开更多
As a platform for longer-term continuous moon-based earth radiation observation(MERO)which includes reflected solar short-wave(SW)radiation and long-wave infrared(LW)radiation,the huge lunar surface space can provide ...As a platform for longer-term continuous moon-based earth radiation observation(MERO)which includes reflected solar short-wave(SW)radiation and long-wave infrared(LW)radiation,the huge lunar surface space can provide multiple location choices.It is important to analyze the influence of lunar surface position on irradiance which is the aim of the present work based on a radiation heat transfer model.To compare the differences caused by positions,the site of 0°E 0°N was selected as the reference site and a good agreement of the calculation results was verified by the comparison with the NISTAR’s actual detected data.By analyzing the spatial characteristics of the irradiance,the results showed that the irradiance on the lunar surface was of circular distribution and the instrument that was placed in the region of 65°W-65°E and 65°S-65°N could detect the irradiance most effectively.The relative deviation between the reference site and the marginal area(region of>65°S or 65°N or>65°W or 65°E)was less than 0.9 mW∙m^(-2) and the small regional differences make a small-scale network conducive to radiometric calibration between instruments.To achieve accurate measurement of the irradiance,the sensitivity design goal of the MERO instrument should be better than 1 mW∙m^(-2) in a future actual design.Because the lunar polar region is the priority region for future exploration,the irradiance at the poles has also been analyzed.The results show that the irradiance changes periodically and exhibits complementary characteristics of time.The variation range of irradiance for short-wave radiation is greater than longwave radiation and the irradiance of SW reaches the maximum at different times.The MERO at the polar region will provide valuable practical experiment for the followup study of the moon-based earth observation in low latitudes.展开更多
基金Under the auspices the Fundamental Research Funds for the Central Universities,China(No.2017TD-26)the Plan for Changbai Mountain Scholars of Jilin Province,China(No.JJLZ[2015]54)
文摘The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satellite observations, the spatio-temporal characteristics of MILS_BRF data have rarely been explicitly and comprehensively analysed. Results from 5-yr(2011–2015) of MILS_BRF dataset from a typical region in central Northeast Asia as the study area showed that the monthly area coverage as well as MILS_BRF data quantity varies significantly, from the highest in October(99.05%) through median in June/July(78.09%/75.21%) to lowest in January(18.97%), and a large data-vacant area exists in the study area during four consecutive winter months(December through March). The data-vacant area is mainly composed of crop lands and cropland/natural vegetation mosaic. The amount of data within the principal plane(PP)±30°(nPP) or cross PP ±30°(nCP), varies intra-annually with significant differences from different view zeniths or forward/backward scattering directions. For example, multiple off-nadir cameras have nPP but no nCP data for up to six months(September through February), with the opposite occurring in June and July. This study provides explicit and comprehensive information about the spatio-temporal characteristics of product coverage and observation geometry of MILS_BRF in the study area. Results provide required user reference information for MILS_BRF to evaluate performance of BRDF models or to compare with other satellite-derived BRF or albedo products. Comparing this final product to on-satellite observations, what was found here reveals a new perspective on product spatial coverage and observation geometry for multi-angle remote sensing.
文摘Lunar occultation observations are useful in refining lunar limb profiles, which will be used for the analysis of solar eclipse observations to detect the variation of the solar diameter, and in detecting the possible errors of the Hipparcos proper motion system. Many lunar occultations have been observed in Japan. Some of the results are shown in this paper to encourage people in the world to observe more lunar occultations with better accuracies.
基金Project(020301)supported by the Manned Spaceflight Advanced Research,ChinaProject(14JJ3024)supported by Hunan Natural Science Foundation,China
文摘An extended-state-observer(ESO) based predictive control scheme is proposed for the autopilot of lunar landing.The slosh fuel masses exert forces and torques on the rigid body of lunar module(LM),such disturbances will dramatically undermine the stability of autopilot system.The fuel sloshing dynamics and uncertainties due to the time-varying parameters are considered as a generalized disturbance which is estimated by an ESO from the measured attitude signals and the control input signals.Then a continuous-time predictive controller driven by the estimated states and disturbances is designed to obtain the virtual control input,which is allocated to the real control actuators according to a deadband logic.The 6-DOF simulation results reveal the effectiveness of the proposed method when dealing with the fuel sloshing dynamics and parameter perturbations.
基金supported by the National Natural Science Foundation of China(Grant No.41590855)。
文摘As a platform for longer-term continuous moon-based earth radiation observation(MERO)which includes reflected solar short-wave(SW)radiation and long-wave infrared(LW)radiation,the huge lunar surface space can provide multiple location choices.It is important to analyze the influence of lunar surface position on irradiance which is the aim of the present work based on a radiation heat transfer model.To compare the differences caused by positions,the site of 0°E 0°N was selected as the reference site and a good agreement of the calculation results was verified by the comparison with the NISTAR’s actual detected data.By analyzing the spatial characteristics of the irradiance,the results showed that the irradiance on the lunar surface was of circular distribution and the instrument that was placed in the region of 65°W-65°E and 65°S-65°N could detect the irradiance most effectively.The relative deviation between the reference site and the marginal area(region of>65°S or 65°N or>65°W or 65°E)was less than 0.9 mW∙m^(-2) and the small regional differences make a small-scale network conducive to radiometric calibration between instruments.To achieve accurate measurement of the irradiance,the sensitivity design goal of the MERO instrument should be better than 1 mW∙m^(-2) in a future actual design.Because the lunar polar region is the priority region for future exploration,the irradiance at the poles has also been analyzed.The results show that the irradiance changes periodically and exhibits complementary characteristics of time.The variation range of irradiance for short-wave radiation is greater than longwave radiation and the irradiance of SW reaches the maximum at different times.The MERO at the polar region will provide valuable practical experiment for the followup study of the moon-based earth observation in low latitudes.
