Daily Surface Albedo Estimated From DSCOVR/EPIC

The surface broadband albedo is defined as the ratio of the reflected solar radiation on the surface to the total received solar radiation on the surface,which reflects the ability of the surface to reflect solar radiation energy,and it is an important factor affecting atmospheric motion and the balance of surface energy budget.However,the existing albedo products rarely meet the requirements of the daily scale,which has a great impact on regional climate change research and rapid dynamic change analysis of the surface.Therefore,the retrieval of surface broadband albedo with high temporal resolution is of great significance.The Deep Space Climate Observatory(DSCOVR)was launched into the Sun-Earth's first Lagrangian(L1)orbit on February 11,2015,which is a unique observation location.The Earth Polychromatic Imaging Camera(EPIC)is an imager onboard the DSCOVR,which can provide a global spectral image of the entire sun-light surface at point L1 of the sun and the earth.EPIC can provide observation data with high time resolution,and it is of great significance to explore the feasibility of the new sensor DSCOVR/EPIC data to retrieve high-temporal ground surface albedo.This paper firstly summarizes the existing surface albedo products,and the inversion models of albedo products as well as its applications.Then,according to the characteristics of DSCOVR/EPIC sensors,the inversion method of EPIC surface albedo is estimated based on the direct estimation method.Firstly,the linear relationship between the broadband albedo and the surface directional reflectance is established,and then the coefficients of the linear relationship are calculated according to the prior BRDF dataset.Finally,the coefficients are converted into regression coefficients based on EPIC sensors by means of band conversion.The hourly EPIC albedo was estimated by the EPIC observations data with high temporal resolution.The accuracy of EPIC albedo under different ground cover types was validated using Ameri Flux ground observation data.Firstly,the time series characteristics of albedo under different land cover types are analyzed.Then the accuracy of EPIC albedo estimation under different land cover types are validated.Finally,the diurnal variation characteristics of EPIC albedo are analyzed,including the validation of diurnal variation of EPIC albedo and the changes characteristics analysis of EPIC hourly albedo in one day under different surface cover types.The results show that the consistency of EPIC albedo and ground observation data is better under different surface cover types.Affected by the hotspot observation direction,the EPIC albedo is overestimated.This feature is even more apparent at sites where the type of surface cover is Evergreen Needleaf,open Shrublands,and Savannas.It can be seen from the analysis of diurnal variation changes in EPIC albedo that the albedo changes within a day,showing a "U" shape.This change is related to the solar altitude angle,that is,the surface albedo decreases with the increase of the solar altitude small.