Accessing Station Data

Obtaining a quick overview of the dataset

The function dataInventory is intended for a quick overview of the data contained in the dataset. In the case of stations data, the main argument to be provided is the path to the directory where the dataset (stations.txt, variables.txt and associated data) are stored (see this link for details on station data format).

For instance, this is a quick overview of the built-in dataset in the downscaleR package using dataInventory:

> di <- dataInventory("inst//datasets//observations//GSN_Iberia")
[2014-06-03 09:36:27] Doing inventory ...
[2014-06-03 09:36:27] Done.

The object loaded contains all the necessary information in order to make a call to the loading function loadObservations, including station codes, geolocation and details on the variable names, units ... :

> str(di)
List of 3
 $ Stations     :List of 4
  ..$ station_id    : chr [1:6] "SP000008027" "SP000008181" "SP000008202" "SP000008215" ...
  ..$ xyCoords  : num [1:6, 1:2] -2.04 2.07 -5.5 -4.01 -1.86 ...
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : chr [1:6] "SP000008027" "SP000008181" "SP000008202" "SP000008215" ...
  .. .. ..$ : chr [1:2] "lon" "lat"
  ..$ times         :List of 3
  .. ..$ startDate: POSIXlt[1:1], format: "1979-01-01"
  .. ..$ endDate  : POSIXlt[1:1], format: "2012-12-31"
  .. ..$ timeStep :Class 'difftime'  atomic [1:1] 24
  .. .. .. ..- attr(*, "units")= chr "hours"
  ..$ other.metadata:List of 4
  .. ..$ altitude    : int [1:6] 251 4 790 1894 704 90
  .. ..$ location    : chr [1:6] "SAN SEBASTIAN - IGUELDO" "BARCELONA/AEROPUERTO" "SALAMANCA AEROPUERTO" "NAVACERRADA" ...
  .. ..$ WMO_Id      : int [1:6] 8027 8181 8202 8215 8280 8410
  .. ..$ Koppen.class: chr [1:6] "Cfb" "Csa" "BSk" "Csb" ...
 $ Variables    :'data.frame':	3 obs. of  4 variables:
  ..$ variable    : Factor w/ 3 levels "precip","tmax",..: 1 3 2
  ..$ longname    : Factor w/ 3 levels "maximum daily temperature",..: 3 2 1
  ..$ unit        : Factor w/ 2 levels "0.1 degC","0.1 mm": 2 1 1
  ..$ missing.code: Factor w/ 1 level "NaN": 1 1 1
 $ Summary.stats: NULL

Note that the last element of the inventory, named {{{Summary.stats}}} is NULL. Bt default, the inventory will return the basic information, but setting the argument {{{return.stats}}} to TRUE will return also a table summarizing the characteristics of the data (percentage of missing data, mean, min and max values):

> di2 <- dataInventory("inst//datasets//observations//GSN_Iberia", return.stats= TRUE)
[2014-06-03 09:51:18] Doing inventory ...
[2014-06-03 09:51:19] Done.

> di2$Summary.stats
$missing.percent
            precip tmin tmax
SP000008027    0.6  2.3  4.2
SP000008181    0.7  1.7  1.1
SP000008202    0.5  4.5  0.8
SP000008215    0.6  2.7  2.3
SP000008280    0.5 17.8  4.1
SP000008410    0.9 10.1  6.0

$min
            precip  tmin  tmax
SP000008027   -0.3 -10.0  -3.5
SP000008181    0.0  -7.2   0.0
SP000008202    0.0 -12.0  -1.4
SP000008215    0.0 -17.5 -11.0
SP000008280    0.0 -13.4  -1.8
SP000008410    0.0  -8.2   0.0

$max
            precip tmin tmax
SP000008027   93.0 25.2 38.6
SP000008181  175.1 26.8 37.4
SP000008202   50.3 22.0 41.0
SP000008215  111.8 20.6 31.8
SP000008280  146.6 23.4 42.0
SP000008410  154.3 27.0 46.6

$mean
               precip      tmin     tmax
SP000008027 1.2266499 10.621573 16.58673
SP000008181 1.5895889 11.803554 20.44687
SP000008202 1.0108198  5.791200 18.73546
SP000008215 1.5650255  3.303088 10.94361
SP000008280 0.9700607  7.756689 20.23754
SP000008410 1.5544916 11.311057 24.63882

Loading station data

The function loadObservations is the interface to acces observational datasets. There are several ways in which observations data can be queried. The most common cases are next presented.

Loading station data from station codes

Given the station codes provided by the inventory, it is possible to retrieve a time series for a selected station or several time series for several stations directly by the identification codes. This will load summer temperature data (JJA) for the period 1981-2000 for two stations: Albacete - Los Llanos and Cordoba - Aeropuerto:

> example1 <- loadObservations(source.dir="inst//datasets//observations//GSN_Iberia", var="tmax", stationID = c("SP000008280", "SP000008410"), season = 6:8, years = 1981:2000)
[2014-06-03 10:13:30] Loading data ...
[2014-06-03 10:13:30] Retrieving metadata ...
[2014-06-03 10:13:30] Done.
> str(example1)
List of 6
 $ variable    : chr "tmax"
 $ station_id  : chr [1:2] "SP000008280" "SP000008410"
 $ xyCoords: num [1:2, 1:2] -1.86 -4.85 38.95 37.84
  ..- attr(*, "dimnames")=List of 2
  .. ..$ : chr [1:2] "SP000008280" "SP000008410"
  .. ..$ : chr [1:2] "longitude" "latitude"
 $ time        :List of 2
  ..$ Start: POSIXlt[1:1840], format: "1981-06-01" "1981-06-02" "1981-06-03" "1981-06-04" ...
  ..$ End  : POSIXlt[1:1840], format: "1981-06-02" "1981-06-03" "1981-06-04" "1981-06-05" ...
 $ metadata    :List of 4
  ..$ altitude    : int [1:2] 704 90
  ..$ location    : chr [1:2] "ALBACETE LOS LLANOS" "CORDOBA AEROPUERTO"
  ..$ WMO_Id      : int [1:2] 8280 8410
  ..$ Koppen.class: chr [1:2] "BSk" "Csa"
 $ Data        :'data.frame':	1840 obs. of  2 variables:
  ..$ SP000008280: num [1:1840] 27.4 26.6 23.2 26.4 30.2 33.6 34.6 35.6 35 32.4 ...
  ..$ SP000008410: num [1:1840] 26.8 26.8 26.4 31 33.6 35.6 37.4 37 36.6 39.6 ...

This is an example plot of the time series returned. Note that time is defined by lower and upper time bounds, rather than one single verification date:

> plot(example1$time$Start, example1$Data$SP000008410, ty = 'l', col = "blue")
> lines(example1$time$Start, example1$Data$SP000008280, ty = 'l', col = "red")

Loading station data from geographical coordinates

Alternatively, we can choose a location by its coordinates. From the dataset inventory, we know the geographical coordinates of the Albacete - Los Llanos station (-1.8631E, 38.9519N):

> di$Stations$xyCoords
                lon     lat
SP000008027 -2.0392 43.3075
SP000008181  2.0697 41.2928
SP000008202 -5.4981 40.9592
SP000008215 -4.0103 40.7806
SP000008280 -1.8631 38.9519
SP000008410 -4.8458 37.8442

We can introduce these coordinates in the lonLim and latLim arguments. Note that it is not necessary to specify all the decimals, as the function will take care of finding the closest station to the given coordinate:

> example2 <- loadObservations(source.dir="inst//datasets//observations//GSN_Iberia", var="tmax", lonLim = -1.9, latLim = 39, season = 6:8, years = 1981:2000)
[2014-06-03 10:36:26] Closest station located at 0.0606 spatial units from the specified [lonLim,latLim] coordinate
[2014-06-03 10:36:26] Loading data ...
[2014-06-03 10:36:26] Retrieving metadata ...
[2014-06-03 10:36:26] Done.
> str(example2)
List of 6
 $ variable    : chr "tmax"
 $ station_id  : chr "SP000008280"
 $ xyCoords: num [1, 1:2] -1.86 38.95
  ..- attr(*, "dimnames")=List of 2
  .. ..$ : chr "SP000008280"
  .. ..$ : chr [1:2] "longitude" "latitude"
 $ time        :List of 2
  ..$ Start: POSIXlt[1:1840], format: "1981-06-01" "1981-06-02" "1981-06-03" "1981-06-04" ...
  ..$ End  : POSIXlt[1:1840], format: "1981-06-02" "1981-06-03" "1981-06-04" "1981-06-05" ...
 $ metadata    :List of 4
  ..$ altitude    : int 704
  ..$ location    : chr "ALBACETE LOS LLANOS"
  ..$ WMO_Id      : int 8280
  ..$ Koppen.class: chr "BSk"
 $ Data        :'data.frame':	1840 obs. of  1 variable:
  ..$ SP000008280: num [1:1840] 27.4 26.6 23.2 26.4 30.2 33.6 34.6 35.6 35 32.4 ...

Selection of station data within a given geographical bounding box

A particular case of selection by coordinates is when all data within a given bounding box is desired. In this case, the lonLim and latLim arguments are filled with a vector of length two, defining the corners of the bounding box. For instance:

> example3 <- loadObservations(source.dir="inst//datasets//observations//GSN_Iberia", var="tmax", lonLim = c(-5,5), latLim = c(37,40), season = 6:8, years = 1981:2000)
[2014-06-03 10:43:59] Loading data ...
[2014-06-03 10:44:00] Retrieving metadata ...
[2014-06-03 10:44:00] Done.
> str(example3)
List of 6
 $ variable    : chr "tmax"
 $ station_id  : chr [1:2] "SP000008280" "SP000008410"
 $xyCoords: num [1:2, 1:2] -1.86 -4.85 38.95 37.84
  ..- attr(*, "dimnames")=List of 2
  .. ..$ : chr [1:2] "SP000008280" "SP000008410"
  .. ..$ : chr [1:2] "longitude" "latitude"
 $ time        :List of 2
  ..$ Start: POSIXlt[1:1840], format: "1981-06-01" "1981-06-02" "1981-06-03" "1981-06-04" ...
  ..$ End  : POSIXlt[1:1840], format: "1981-06-02" "1981-06-03" "1981-06-04" "1981-06-05" ...
 $ metadata    :List of 4
  ..$ altitude    : int [1:2] 704 90
  ..$ location    : chr [1:2] "ALBACETE LOS LLANOS" "CORDOBA AEROPUERTO"
  ..$ WMO_Id      : int [1:2] 8280 8410
  ..$ Koppen.class: chr [1:2] "BSk" "Csa"
 $ Data        :'data.frame':	1840 obs. of  2 variables:
  ..$ SP000008280: num [1:1840] 27.4 26.6 23.2 26.4 30.2 33.6 34.6 35.6 35 32.4 ...
  ..$ SP000008410: num [1:1840] 26.8 26.8 26.4 31 33.6 35.6 37.4 37 36.6 39.6 ...

Loading all stations

By default, the arguments defining the spatial domain of the query (lonLim and latLim or stationID) are NULL. If none of them is indicated, the function will load all available stations for the time domain selected:

> example4 <- loadObservations(source.dir="inst//datasets//observations//GSN_Iberia", var="tmax", season = 6:8, years = 1981:2000)
[2014-06-03 10:47:09] Loading data ...
[2014-06-03 10:47:09] Retrieving metadata ...
[2014-06-03 10:47:09] Done.
> str(example4)
List of 6
 $ variable    : chr "tmax"
 $ station_id  : chr [1:6] "SP000008027" "SP000008181" "SP000008202" "SP000008215" ...
 $ xyCoords: num [1:6, 1:2] -2.04 2.07 -5.5 -4.01 -1.86 ...
  ..- attr(*, "dimnames")=List of 2
  .. ..$ : chr [1:6] "SP000008027" "SP000008181" "SP000008202" "SP000008215" ...
  .. ..$ : chr [1:2] "longitude" "latitude"
 $ time        :List of 2
  ..$ Start: POSIXlt[1:1840], format: "1981-06-01" "1981-06-02" "1981-06-03" "1981-06-04" ...
  ..$ End  : POSIXlt[1:1840], format: "1981-06-02" "1981-06-03" "1981-06-04" "1981-06-05" ...
 $ metadata    :List of 4
  ..$ altitude    : int [1:6] 251 4 790 1894 704 90
  ..$ location    : chr [1:6] "SAN SEBASTIAN - IGUELDO" "BARCELONA/AEROPUERTO" "SALAMANCA AEROPUERTO" "NAVACERRADA" ...
  ..$ WMO_Id      : int [1:6] 8027 8181 8202 8215 8280 8410
  ..$ Koppen.class: chr [1:6] "Cfb" "Csa" "BSk" "Csb" ...
 $ Data        :'data.frame':	1840 obs. of  6 variables:
  ..$ SP000008027: num [1:1840] 29 22.4 15.2 18.2 23 20 27.4 28.8 17.6 16.8 ...
  ..$ SP000008181: num [1:1840] 23.6 23.4 26 22.2 23.4 24.4 24.8 26.8 28 27.4 ...
  ..$ SP000008202: num [1:1840] 22.6 19 18 22.4 25.7 28.4 29 29 26.7 29.8 ...
  ..$ SP000008215: num [1:1840] 12.6 11.8 7.4 14.6 18.2 19.4 21.6 21.4 19.8 23.2 ...
  ..$ SP000008280: num [1:1840] 27.4 26.6 23.2 26.4 30.2 33.6 34.6 35.6 35 32.4 ...
  ..$ SP000008410: num [1:1840] 26.8 26.8 26.4 31 33.6 35.6 37.4 37 36.6 39.6 ...

The same behaviour can be expected with the time definition of the query. For instance, when season and/or years are left to their default value NULL, all months and/or years within the dataset will be returned.

Plotting example

The next example plots the time series retrieved in the example 1:

> plot(example1$time$Start, example1$Data$SP000008410, ty = 'l', col = "blue", xlab = "time", ylab = "T (ºC)")
> lines(example1$time$Start, example1$Data$SP000008280, ty = 'l', col = "red")
> legend("bottomright", c("Albacete", "Cordoba"), col = c("red", "blue"), lty = 1)
> title("Tmax - JJA (1981-2000)")