TrendAAT: Trend estimation based on annual aggregated time series
In greenbrown: Land Surface Phenology and Trend Analysis

Description Usage Arguments Value Author(s) References See Also Examples

The function aggregates a time series to annual values and computes breakpoints and trends on the annual aggregated time series. The function can be applied to gridded (raster) data using the function TrendRaster. A detailed description of this method can be found in Forkel et al. (2013).

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TrendAAT(Yt, mosum.pval = 0.05, 
    h = 0.15, breaks = NULL, 
    funAnnual = mean)

`Yt`	univariate time series of class `ts`
`mosum.pval`	Maximum p-value for the OLS-MOSUM test in order to search for breakpoints. If p = 0.05, breakpoints will be only searched in the time series trend component if the OLS-MOSUM test indicates a significant structural change in the time series. If p = 1 breakpoints will be always searched regardless if there is a significant structural change in the time series or not. See `sctest` for details.
`h`	minimal segment size either given as fraction relative to the sample size or as an integer giving the minimal number of observations in each segment. See `breakpoints` for details.
`breaks`	maximal number of `breaks` to be calculated (integer number). By default the maximal number allowed by `h` is used. See `breakpoints` for details.
`funAnnual`	function to aggregate time series to annual values The default function is the mean (i.e. trend calculated on mean annual time series). See example section for other examples.

The function returns a list of class "Trend".

Matthias Forkel <matthias.forkel@tu-dresden.de> [aut, cre]

Forkel, M., N. Carvalhais, J. Verbesselt, M. Mahecha, C. Neigh and M. Reichstein (2013): Trend Change Detection in NDVI Time Series: Effects of Inter-Annual Variability and Methodology. - Remote Sensing 5.

Trend, TrendRaster

# calculate trend on mean annual NDVI values
trd.annualmean <- TrendAAT(ndvi)
trd.annualmean
plot(trd.annualmean)

TrendLongestSEG(trd.annualmean)

# calculate annual trend but don't apply MOSUM test for structural change
trd.annualmean <- TrendAAT(ndvi, mosum.pval=1)
trd.annualmean
plot(trd.annualmean)

# calculate trend on annual peak (maximum) NDVI
trd.annualmax <- TrendAAT(ndvi, funAnnual=max, mosum.pval=1)
trd.annualmax 
plot(trd.annualmax)

# calculate trend on an annual quantile NDVI (e.g. upper 0.9 quantile)
fun <- function(x, ...) { quantile(x, 0.9, ...) }
trd.annualquantile9 <- TrendAAT(ndvi, funAnnual=fun, mosum.pval=1)
trd.annualquantile9
plot(trd.annualquantile9)