Filter to remove noise in light intensity measurements during the night

Description

The filter identifies and removes light intensities oczillating around the baseline or few light intensities resulting in a short light peak during the night. Such noise during the night will increase the calculated twilight events using the function twilightCalc and therewith the manual work to remove these false twilight events.

Usage

lightFilter(light, baseline = NULL, iter = 2)

Arguments

Details

The filter searches for light levels above the baseline and compares the prior and posterior levels. If these values are below the threshold the particular light level will be reduced to the baseline. A few (usually two) iterations might be enough to remove most noise during the night (however, not if such noise occurs at the begining or at the end were not enough prior or posterior values are available).

Value

numerical vector with the new light levels. Same length as the initial light vector.

Author(s)

Simeon Lisovski

Examples

night <- rep(0,50); night[runif(4,0,50)] <- 10; night[runif(4,0,50)] <- -5
nightday <- c(night,rep(30,50))
plot(nightday,type="l",ylim=c(-5,30),ylab="light level",xlab="time (time)")
light2 <- lightFilter(nightday, baseline=0, iter=4)
lines(light2,col="red")
legend("bottomright",c("before","after"),lty=c(1,1),col=c("black","red"),bty="n")

Results

R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)

R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.

R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.

Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.

> library(GeoLight)
Loading required package: maps

 # maps v3.1: updated 'world': all lakes moved to separate new #
 # 'lakes' database. Type '?world' or 'news(package="maps")'.  #


> png(filename="/home/ddbj/snapshot/RGM3/R_CC/result/GeoLight/lightFilter.Rd_%03d_medium.png", width=480, height=480)
> ### Name: lightFilter
> ### Title: Filter to remove noise in light intensity measurements during
> ###   the night
> ### Aliases: lightFilter
> 
> ### ** Examples
> 
> night <- rep(0,50); night[runif(4,0,50)] <- 10; night[runif(4,0,50)] <- -5
> nightday <- c(night,rep(30,50))
> plot(nightday,type="l",ylim=c(-5,30),ylab="light level",xlab="time (time)")
> light2 <- lightFilter(nightday, baseline=0, iter=4)
> lines(light2,col="red")
> legend("bottomright",c("before","after"),lty=c(1,1),col=c("black","red"),bty="n")
> 
> 
> 
> 
> 
> dev.off()
null device 
          1 
>