Forecast ndvi using a seasonal auto ARIMA
fcast_ndvi(hist_ndvi, level, lead, moons = NULL)
historic ndvi data
specify "monthly" or "newmoon"
number of steps forward to forecast
moon data (required if level = "newmoon")
a data.frame with time and ndvi values
ndvi values are forecast using auto.arima with seasonality (using a Fourier transform)