as defined in Basler et al. 2016 (Agr. For. Meteorlogy) with a sigmoidal temperature response (Kramer 1994)
TTs(par, data)
a vector of parameter values, this is functions specific
input data (see reference for detailed description), data should be formatted using flat_format()
raster or vector with estimated phenophase timing (in DOY)
if (FALSE) {
estimate <- TTs(data = data, par = par)
}