compwaveconv {seawaveQ}

Seasonal Wave Computation

Description

Function to compute seasonal wave.

Usage

compwaveconv(cmaxt, jmod, hlife)

Arguments

cmaxt

is the time of the maximum chemical concentration, decimal time in years.

jmod

is the choice of model or pulse input function, an integer 1 through 14.

hlife

is the model half-life in months, 1 to 4 months

Value

A numeric vector of size 361 with discrete values of the seasonal wave for decimal season seq(0,1,1/360).

Note

The seasonal wave is a dimensionless, periodic function of time with an annual cycle, similar to a mixture of sine and cosine functions often used to model seasonality in concentration data. However, the seasonal wave is better suited for modeling seasonal behavior of pesticide data than a mixture of sines and cosines. The pulse input function, represented by jmod, has either one or two distinct application seasons (when pesticides may be transported to the stream) of lengths from 1 to 6 months. Therefore, 56 (14x4) choices for the wave function are available. The numeric vector is a discrete approximation of the continuous wave function defined on the interval 0 to 1.

Author(s)

Aldo V. Vecchia

References

Vecchia, A.V., Martin, J.D., and Gilliom, R.J., 2008, Modeling variability and trends in pesticide concentrations in streams: JAWRA Journal of the American Water Resources Association, v. 44, p. 1308–1324, https://doi.org/10.1111/j.1752-1688.2008.00225.x.

Examples

# evaluate seasonal wave for specified decimal seasons
# these example decimal dates represent days at points 0.25, 0.5, and 
# 0.75 percent of the way through the year and the end of the year
dseas <- c(0.25, 0.5, 0.75, 1)
swave <- compwaveconv(cmaxt = 0.483, jmod = 2, hlife = 4)
swave[floor(360 * dseas)]
plot(seq(0, 1, 1/360), swave, typ = "l")