isolate.signal {AQEval}

isolateContribution

Description

Environmental time-series signal processing: Contribution isolation based on background subtraction, deseasonalisation and/or deweathering.

Usage

isolateContribution(
  data,
  pollutant,
  background = NULL,
  deseason = TRUE,
  deweather = TRUE,
  method = 2,
  add.term = NULL,
  formula = NULL,
  output = "mean",
  ...
)

Arguments

data

Data source, typically data.frame (or similar), containing all time-series to be used when applying signal processing.

pollutant

The column name of the data time-series to be signal processed.

background

(optional) if supplied, the background time-series to use as a background correction. See below.

deseason

logical or character vector, if TRUE (default), the pollutant is deseasonalised using day.hour and year.day frequency terms, all calculate from the data time stamp, assumed to be date in data. Other options: FALSE to turn off deseasonalisation; or a character vector of frequency terms if user-defining. See below.

deweather

logical or character vector, if TRUE (default), the data is deweathered using wind speed and direction, assumed to be ws and wd in data). Other options: FALSE to turn off deweathering; or a character vector of data column names if user-defining. See below.

method

numeric, contribution isolation method (default 2). See Note.

add.term

extra terms to add to the contribution isolation model; ignore for now (in development).

formula

(optional) Signal isolate model formula; this allows user to set the signal isolation model formula directly, but means function arguments background, deseason and deweather will be ignored.

output

output options; currently, 'mean', 'model', and 'all'; but please note these are in development and may be subject to change.

...

other arguments; ignore for now (in development)

Details

isolateContribution estimates and subtracts pollutant variance associated with factors that may hinder break-point/segment analysis:

• Background Correction If applied, this fits the supplied background time-series as a spline term: s(background).

• Seasonality If applied, this fits regular frequency terms, e.g. day.hour, year.day, as spline terms, default TRUE is equivalent to s(day.hour) and s(year.day). All terms are calculated from date column in data.

• Weather If applied, this fits time-series of identified meteorological measurements, e.g. wind speed and direction (ws and wd in data). If both ws and wd are present these are fitted as a tensor term te(ws, wd). Other deweathering terms, if included, are fitted as spline term s(term). The default TRUE is equivalent to te(ws, wd).

Using the supplied arguments, it builds a signal (mgcv) GAM model, calculates, and returns the mean-centred residuals as an estimate of the isolated local contribution.

Value

isolateContribution returns a vector of predictions of the pollutant time-series after the requested signal isolation.

Note

method was included as part of method development and testing work, and retained for now. Please ignore for now.

Author(s)

Karl Ropkins

References

Regarding mgcv GAM fitting methods, see Wood (2017) for general introduction and package documentation regarding coding (mgcv):

Wood, S.N. (2017) Generalized Additive Models: an introduction with R (2nd edition), Chapman and Hall/CRC.

Regarding isolateContribution, see:

Ropkins et al (In Prep).

See Also

Regarding seasonal terms and frequency analysis, see also stl and spectralFrequency.

mgcv, gam.

Examples

#fitting a simple deseasonalisation, deweathering
#and background correction (dswb) model to no2:

aq.data$dswb.no2 <- isolateContribution(aq.data,
                        "no2", background="bg.no2")

#compare at 7 day resolution:
temp <- openair::timeAverage(aq.data, "7 day")

#without dswb
quantBreakPoints(temp, "no2", test=FALSE, h=0.1)

#with dswb
quantBreakPoints(temp, "dswb.no2", test=FALSE, h=0.1)