Phenological parameters

Phenological parameters

Abstract

Phenology - study of the timing of recurring natural phenomena, the causes of their timing with regard to biotic and abiotic forces, and the interrelation among phases of the same or different species. Examples of such phenomena include the date of emergence of leaves and flowers, date of leaf coloring and fall in deciduous trees etc. Previously phenological research was based on carfull year-after-year observation of certain species of plants and accurate recordings of their timings to make inferences about changes in climate. Now, one of the modern approaches suggests using not vegetation itself but on this proxies, for example NDVI derivable each day from satellite observation. Such data is available for free and generated by MODIS and AVHRR cameras onboard TERRA, AQUA and NOAA-series satellites. Dynamics of such data over time is highly correlated with typical green vegetation growth stages (emergence, vigor/growth, maturity, and harvest/senescence).

1. Start of season - time for which the left edge has increased to a user defined level (often 20% of the seasonal amplitude) measured from the left minimum level.

2. End of season - time for which the right edge has decreased to a user defined level measured from the right minimum level.

3. Length of the season - time from the start to the end of the season.

4. Base level - given as the average of the left and right minimum values.

5. Time for the middle of the season - computed as the mean value of the times for which, respectively, the left edge has increased to the 80 % level and the right edge has decreased to the 80 % level.

6. Peak (season maximum) - largest data value for the fitted function during the season;

7. Seasonal amplitude - difference between the peak value and the base level.

8. Rate of increase at the beginning of the season - the ratio between the values evaluated at the season start and at the left 80 % level divided by the corresponding time difference.

9. Rate of decrease at the end of the season - the ratio between the values evaluated at the season end and at the right 80 % level divided by the corresponding time difference.

10. Large seasonal integral - integral of the function describing the season from the season start to the season end.

11. Small seasonal integral - integral of the difference between the function describing the season and the base level from season start to season end.