Evaluation of satellite land surface albedo products over China using ground-measurements

Land surface albedo(LSA)is an important parameter in surface energy balance and global climate change.It has been used in the fields of energy budgets,climate dynamics,and land surface processes.To apply satellite LSA products more widely,the product accuracy needs to be evaluated at different scales and under atmospheric and surface conditions.This study validates and analyzes the errors of the LSA datasets from the Global LAnd Surface Satellites(GLASS)product,the European Space Agency’s Earth Observation Envelope Programme(GlobAlbedo),the Quality Assurance for Essential Climate Variables(QA4ECV)project,the Gap-filled Snow-free Bidirectional Reflectance Distribution Function(BRDF)parameters product(MCD43GF),and the Satellite Application Facility on Climate Monitoring(CM SAF)Albedo dataset from the AVHRR data(CLARA-SAL)against the Chinese Ecosystem Research Network(CERN)measurements at different spatiotemporal scales over China from 2005 to 2015.The results show that LSA estimated by GLASS agrees well with the CERN measurements on a continental scale.The GLASS product is characterized by a correlation coefficient of 0.80,a root-mean-square error of 0.09,and a mean absolute error of 0.06.The consistency between GLASS,GlobAlbedo,and CLARA-SAL is slightly lower over the regions with high aerosol optical depth(AOD)(e.g.Sichuan Basin,northern China)and high cloud cover compared with that in regions with lower AOD and low cloud cover.The estimation errors are related to varying atmospheric and surface conditions and increase with increasing AOD and cloud cover and decreasing enhanced vegetation index.Therefore,algorithms under complex atmospheric and surface conditions(e.g.high AOD,sparse vegetation)should be optimized to improve the accuracy of LSA products.

THE EMERGING CHALLENGE:THE VALIDITY OF COMPUTATIONAL ORGANIZATION MODEL AND METHODOLOGY

The validity of the computational organization model is a necessary condition and also poses a bottleneck in computational organization theory development.Established on the frontline of computational organization theory,this paper provides an overall discussion on the difficulties in validation and validation methodology of the computational organization model.First,different from natural engineering system model,and also exceeding the traditional empirical method,the computational organization model is faced with various subjective and objective difficulties during the validation progress;second,in developing the situational validation methodology based on relationships among problem field,modeling purpose and referents,it is important for the computational organization model that the validation is conducted according to certain degree;third,the establishment of verification,validation and accreditation approach(VV&A),which is different from the natural engineering system,is an irresistible trend for future development of the computational organization model.Model validation should be focused on concept validation,operation validation,and data validation,as well as the principle of iterative validation approach and such validation should be conducted throughout the modeling process;finally,the validation of computational organization model should be the process to enhance people’s confidence in the model.From the perspective of review,if the model is able to pass through all the validation tests,it is helpful for a better understanding of the model’s ability,limitation and applicability.In this case,research from interdisciplinary experts is required urgently.