<center>Tutorial for merging a WRF output (maximum temperature) with ground observations using `VARMER`</center>

In VARMER: Variational Merging

knitr::opts_chunk$set(echo = TRUE)

About

This vignette describes a basic application of the VARMER library, which provides methods to combine satellite-based or model-based gridded images with ground-based observed time-series [1].

Installation

Install the latest stable version (from CRAN):

install.packages("VARMER")

Setting up the environment

1. Load other packages that will be used in this analysis and VARMER:

library(zoo)
library(sf)
library(raster)
library(tictoc)
library(cluster)
library(parallel)
#library(ggplot2)
library(VARMER)

Loading input data

First, daily time series of maximum temperature observations in 34 stations located in Ecuador will be used for this example, from 2004-01-01 to 2004-01-10, which are available in the ecuador.tmax.zoo dataset provided in the VARMER package (for your own application, this dataset might be read from a CSV file or a zoo file). In addition, the ecuador.tmax.stations.df dataset contains information about the IDs and spatial coordinates of each station (for your own application, this dataset might be read from a CSV file).

data(ecuador.tmax.zoo)
data(ecuador.tmax.stations.df)

Secondly, we need to load the WRF output. For this example, the model-data was obtained from a WRF v3.6.1 simulation at 10Km spatial resolution and at daily temporal resolution.

data(ecuador.tmax.wrf.out)

Basic exploratory data analysis

First, we would like to visualize the first six rows of the spatial metadata:

head(ecuador.tmax.stations.df)

Plotting the daily precipitation time series for the first station (code: M0001).

main <- paste("Daily maximum temperature for the station", ecuador.tmax.stations.df$CODIGO[1])
ylab <- "Maximum temperature [°C]"
x.ts <- ecuador.tmax.zoo[,1]

plot(x.ts, main=main, ylab= ylab, col="blue")
grid()

Plotting the average maximum temperature from WRF output, and overlying the boundaries of the study area (only its first attribute):

wrfout.total <- mean(ecuador.tmax.wrf.out, na.rm=FALSE)

plot(wrfout.total, main = "WRF output [Jan-2004] ", xlab = "Longitude", ylab = "Latitude")

Running VARMER

Setup

Finally, you need to define the output directory (drty.out) before running VARMER. Then, you can run the varmer.ts function as follows:

varmer.ts(x=ecuador.tmax.zoo, x.metadata=ecuador.tmax.stations.df,
          v=ecuador.tmax.wrf.out, lat='LAT', lon='LON',
          drty.out="~/Documentos/dataset_ecuador")

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Expected outputs

If VARMER runs without problems, the final merged product (individual GeoTiff files) will be stored in your user-defined drty.out directory.

Software details

This tutorial was built under:

sessionInfo()$platform
sessionInfo()$R.version$version.string 
paste("VARMER", sessionInfo()$otherPkgs$VARMER$Version)

References

1. Ulloa, J., Samaniego, E., Campozano, L., & Ballari, D. (2018). A variational merging approach to the spatial description of environmental variables. Journal of Geophysical Research: Atmospheres, 123. https://doi.org/10.1002/2017JD027982.

VARMER documentation built on Feb. 8, 2021, 1:07 a.m.