Inter-comparison of phenological measures derived from coarse resolution earth observation and implications for assimilation into dynamic vegetation models

Abstract

Large swath width sensors with short revisit periods (circa. 1 day) between successive data acquisitions of a given point on the Earth's surface provide an excellent opportunity to study the phenological developments of vegetation cover. Although very detailed phenological measurements are probably beyond the scope of such sensors, broad changes in vegetation should be readily detected and this information may be used to constrain and check the performance of dynamic vegetation models. This paper compares time series data from a variety of Earth Observation platforms (principally AVHRR and SPOT-4 VGT) and examines their ability to describe the phenology of the United Kingdom over a period several years. Phenological parameters are derived from vegetation indices and the ability of these parameters to drive or be assimilated into vegetation models is discussed with reference to the Sheffield Dynamic Global Vegetation Model. in the model effects the state of the modelled atmosphere and so there is a feedback loop which allows DVMs to be used as a predictive tool for environmental change. EO data may be used in conjunction with such models in various ways. Broadly speaking these are: to provide driving variables; to be used in data assimilation schemes within the models; and to validate their outputs. DVMs typically have a phenology module which is used to drive the growth of the vegetation based on parameters such as temperature and soil moisture. This paper discusses the potential for EO derived phenology information to be used in conjunction with DVMs.