A novel regression method for harmonic analysis of time series

The figure demonstrates the different regression models derived from the four methods for a Landsat NIR surface reflectance time series with a large gap between March and August, in which HAPO is the only method that is not impacted by this data gap (∼ 4 months) (HAPO: Harmonic Adaptive Penalty Operator; LASSO: least absolute shrinkage and selection operator; OLS: ordinary least squares; and Ridge: Ridge regression). The observation data are acquired from Landsat Analysis Ready Data (ARD) products (https://earthexplorer.usgs.gov/). The location is grassland near Montgomery, Alabama, USA (Latitude: 32.408041°, Longitude −86.272600°).