readcurr: Read AVISO ocean current data

In AustralianAntarcticDivision/raadtools: Tools for Synoptic Environmental Spatial Data

Read AVISO ocean current data

Description

Current data is read from files managed by currentsfiles. Dates are matched to file names by finding the nearest match in time within a short duration. By default only one time step is returned with both U and V components. Multiple dates can be returned for magnitude or direction, U or V only.

Usage

readcurr(
  date,
  time.resolution = c("daily"),
  xylim = NULL,
  lon180 = TRUE,
  magonly = FALSE,
  dironly = FALSE,
  uonly = FALSE,
  vonly = FALSE,
  latest = TRUE,
  returnfiles = FALSE,
  ...,
  inputfiles = NULL
)

Arguments

date	date or dates of data to read, see Details
time.resolution	time resolution to read
xylim	spatial extents to crop from source data, can be anything accepted by extent, see Details
lon180	defaults to TRUE, to "rotate" Pacific view 0, 360 data to Atlantic view -180, 180
magonly	return just the magnitude from the U and V components
dironly	return just the direction from the U and V, in degrees N=0, E=90, S=180, W=270
uonly	return just the U component of velocity
vonly	return just the V component of velocity components, in degrees (0 north, 90 east, 180 south, 270 west)
latest	if TRUE (and date not supplied) return the latest time available, otherwise the earliest
returnfiles	ignore options and just return the file names and dates
...	passed to brick, primarily for filename

Details

These labels 'u', 'v', 'mag', and 'dir' correspond to arguments 'uonly', 'vonly', 'magonly', and 'dironly' which exist to have the function return only the 'u' or 'v' layer (by default both are returned which can only work for a single time step). 'magonly' and 'dironly' are special cases calculated from 'u' and 'v', the magnitude and direction of the field respectively in m/s and degrees from north.

This is the "DT merged all satellites Global Ocean Gridded SSALTO/DUACS Sea Surface Height L4 product and derived variables" See References.

Value

raster object with the "U" (meridional/horizontal/X) and "V" (zonal/vertical/Y) components of velocity in m/s. Setting either of the (mutually exclusive) magonly and dironly arguments returns the magnitude (in m/s) or direction (in degrees relative to North) of the velocity vectors.

Note

These data for daily files are stored in longitude/latitude projection on the sphere between longitudes in the Pacific view [0, 360], the default behaviour is to reset this to Atlantic view [-180, 180] with lon180.

References

http://marine.copernicus.eu

See Also

icefiles for details on the repository of data files, raster for the return value

Examples

## read a single time slice, and plot the directions [0,360) as an image with arrows
x <- readcurr(dironly = TRUE)
## get a local extent for a zoom plot
e <- extent(projectExtent(raster(extent(130, 150, -50, -30), crs = "+proj=longlat"), projection(x)))
x <- crop(readcurr(), e)
crds <- coordinates(x)
scale <- 1.5
vlen <- function(x) sqrt(x[[1]]^2 + x[[2]]^2)
plot(vlen(crop(x, e)))
x1 <- crds[,1]
y1 <- crds[,2]
x2 <- crds[,1] + values(x[[1]]) * scale
y2 <- crds[,2] + values(x[[1]]) * scale
arrows(x1, y1, x2, y2, length = 0.03)

AustralianAntarcticDivision/raadtools documentation built on Nov. 14, 2024, 4:27 p.m.