A phenology-preserving filtering method to reduce noise in NDVI time series

This paper presents a phenology-preserving filtering method as a significant improvement to the standard changing-weight filter method to reduce noise in NDVI time series. Specifically it introduces two new features: (1) replacing the changing-weight filter with a 3-point Gaussian filter to improve the computing efficiency; and (2) introducing a multi-year average NDVI time series to remove the false local minima points. This phenology-preserving filtering method was tested at 178 test points for 15 land cover types and 6 test regions around the world using the 250 m 16-day MODIS NDVI product. The results were evaluated in comparison with the original changing-weight filter and other three popular filtering methods. The visual and quantitative analyses demonstrate that the phenology-preserving filtering method can effectively reduce noise and preserve the integrity of the time series with a high computing efficiency.