MazamaTimeSeries (version 0.3.0)

timeInfo: Get time related information

Description

Calculate the local time at the target location, as well as sunrise, sunset and solar noon times, and create several temporal masks.

The returned dataframe will have as many rows as the length of the incoming UTC time vector and will contain the following columns:

• localStdTime_UTC -- UTC representation of local standard time

• daylightSavings -- logical mask = TRUE if daylight savings is in effect

• localTime -- local clock time

• sunrise -- time of sunrise on each localTime day

• sunset -- time of sunset on each localTime day

• solarnoon -- time of solar noon on each localTime day

• day -- logical mask = TRUE between sunrise and sunset

• morning -- logical mask = TRUE between sunrise and solarnoon

• afternoon -- logical mask = TRUE between solarnoon and sunset

• night -- logical mask = opposite of day

Usage

timeInfo(time = NULL, longitude = NULL, latitude = NULL, timezone = NULL)

Value

A dataframe with times and masks.

Arguments

time

POSIXct vector with specified timezone,

longitude

Longitude of the location of interest.

latitude

Latitude of the location of interest.

timezone

Olson timezone at the location of interest.

Attribution

Internal functions used for ephemerides calculations were copied verbatim from the now deprecated maptools package source code in an effort to reduce the number of package dependencies.

Warning

Compared to NOAA's original Javascript code, the sunrise and sunset estimates from this translation may differ by +/- 1 minute, based on tests using selected locations spanning the globe. This translation does not include calculation of prior or next sunrises/sunsets for locations above the Arctic Circle or below the Antarctic Circle.

Local Standard Time

US EPA regulations mandate that daily averages be calculated based on "Local Standard Time" (LST) (i.e. never shifting to daylight savings). To ease work in a regulatory context, LST times are included in the returned dataframe.

Author

Sebastian P. Luque , translated from Greg Pelletier's VBA code (available from https://ecology.wa.gov/Research-Data/Data-resources/Models-spreadsheets/Modeling-the-environment/Models-tools-for-TMDLs), who in turn translated it from original Javascript code by NOAA (see Details). Roger Bivand adapted the code to work with sp classes. Jonathan Callahan adapted the source code from the maptools package to work with MazmaTimeSeries classes.

Details

NOAA used the reference below to develop their Sunrise/Sunset

https://gml.noaa.gov/grad/solcalc/sunrise.html and Solar Position

https://gml.noaa.gov/grad/solcalc/azel.html Calculators. The algorithms include corrections for atmospheric refraction effects.

Input can consist of one location and at least one POSIXct times, or one POSIXct time and at least one location. solarDep is recycled as needed.

Do not use the daylight savings time zone string for supplying dateTime, as many OS will not be able to properly set it to standard time when needed.

The localStdTime_UTC column in the returned dataframe is primarily for internal use and provides an important tool for creating LST daily averages and LST axis labeling.

References

Meeus, J. (1991) Astronomical Algorithms. Willmann-Bell, Inc.

Examples

library(MazamaTimeSeries)

Carmel <-
  Carmel_Valley %>%
  mts_filterDate(20160801, 20160810)

# Create timeInfo object for this monitor
ti <- timeInfo(
  Carmel$data$datetime,
  Carmel$meta$longitude,
  Carmel$meta$latitude,
  Carmel$meta$timezone
)

t(ti[6:9,])

# Subset the data based on day/night masks
data_day <- Carmel$data[ti$day,]
data_night <- Carmel$data[ti$night,]

# Build two monitor objects
Carmel_day <- list(meta = Carmel$meta, data = data_day)
Carmel_night <- list(meta = Carmel$meta, data = data_night)

# Plot them
plot(Carmel_day$data, pch = 8, col = 'goldenrod')
points(Carmel_night$data, pch = 16, col = 'darkblue')