2.2.3. Inversion Period

The idea of this section is to analyze the effect of using a short versus a long period in the computation of the BRDF parameters. For the short period, we use 3 years to make sure the AVHRR time series has enough observations to allow a reliable estimate of parameters. We divided the data from (1982–1999) into three year intervals 1982–1984, 1985–1987, 1988–1990, 1991–1993, 1994–1996, and 1997–1999, and the data from (2000–2015) in 2000–2002, 2003–2005, 2006–2008, 2009–2011, and 2012–2015. For the long period, we use 18 years for AVHRR-pre and 15 years for MODIS and AVHRR. We compute the BRDF parameters using the VJB inversion and the original sensor's data. In other words, we use MODIS data to calculate MODIS BRDF parameters and AVHRR data to calculate AVHRR BRDF parameters.
