Gao, F, Morisette, JT, Wolfe, RE, Ederer, G, Pedelty, J, Masuoka, E, Myneni, R, Tan, B, Nightingale, J (2008). An algorithm to produce temporally and spatially continuous MODIS-LAI time series. IEEE GEOSCIENCE AND REMOTE SENSING LETTERS, 5(1), 60-64.
Ecological and climate models require high-quality consistent biophysical parameters as inputs and validation sources. NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) biophysical products provide such data and have been used to improve our understanding of climate and ecosystem changes. However, the MODIS time series contains occasional lower quality data, gaps from persistent clouds, cloud contamination, and other gaps. Many modeling efforts, such as those used in the North American Carbon Program, that use MODIS data as inputs require gap-free data. This letter presents the algorithm used within the MODIS production facility to produce temporally smoothed and spatially continuous biophysical data for such modeling applications. We demonstrate the algorithm with an example from the MODIS-leaf-area-index (LAI) product. Results show that the smoothed LAI agrees with high-quality MODIS LAI very well. Higher R-squares and better linear relationships have been observed when high-quality retrieval in each individual tile reaches 40% or more. These smoothed products show similar data quality to MODIS high-quality data and, therefore, can be substituted for low-quality retrievals or data gaps.