sephora-package {sephora}

Statistical Estimation of Phenological Parameters

Description

Estimates phenological dates of satellite imagery time series. Originally conceived to handle MODIS time series (especifically MOD13Q1), this package can handle Earth Observation time series from any satellite mission.

Details

The main function of this package, phenopar, allows a numeric vector containing satellite-based measurements (preferably, vegetation indices for better results). These observations can be construed as realizations of an underlying periodic stochastic process that has been recorded from the first day of the year (DoY) of startYear to the last DoY of endYear. Thus, each numeric vector can be assembled as a matrix whose number of rows and columns equal to length(startYear:endYear) and frequency, respectively, see get_metadata_years. Moreover, each row of this matrix can be thought as the realization of the periodic stochastic process throughout a season. Thus, having multiple measurements of such a process, functional principal component methods are employed to extract an underlying idealized (vegetation index) curve.

The phenological dates that can be estimated with sephora are:

• Green Up (GU).

• Start of Season (SoS).

• Maturity (Mat).

• Senescence (Sen).

• End of Season (EoS).

• Dormancy (Dor).

Data handling

The following functions allow to access numeric vectors of time series satellite imagery, in particular, MOD13Q1 time series starting at February 18, 2000.

fill_initialgap_MOD13Q1	Fill first 3 MOD13Q1 observations
vecFromData	Get numeric vector from an RData file
vecToMatrix	Set numeric vector as a matrix
get_metadata_years	Get metadata useful in certain visualizations

Modeling

The following functions allow to smooth out and fit a regression model based on Functional Principal Components. Applications of these functions allow to estimate phenological parameters of numeric vectors of Earth Observation time series:

ndvi_derivatives	Derivatives of idealized NDVI curve
phenopar	Estimate phenological dates
phenopar_polygon	Estimate phenological dates (parallel processing)

Plotting

Plot methods for numeric and sephora objects:

getSpiralPlot	Spiral plot of polygon-based phenological date estimates
plot.sephora	Plot methods for sephora-class object

Miscellaneous

datesToDoY	Maps estimated phenological dates to days of a year
getDist_phenoParam	Access to vectors of phenological date estimates from a list
global_min_max	Global critical points of a curve on a closed interval
local_min_max	Local critical points of a curve on a union of open intervals

Author(s)

Tecuapetla-Gómez, I. [e-mail]