Chapter 8 Accessing meteorological data

Objectives:

  • This tutorial will walk through the steps required to access meteorological data from the Maricopa Agricultural Center.

Pre-requisites:

  • Need to have R packages tidyverse, jsonlite, and convertr installed.
  • Need to have an internet connection.

8.1 The Maricopa Weather Station

8.1.1 Meteorological data formats

8.1.1.1 Dimensions:

CF standard-name units
time days since 1970-01-01 00:00:00 UTC
longitude degrees_east
latitude degrees_north

8.1.1.2 Variable names and units

CF standard-name units bety isimip cruncep narr ameriflux
air_temperature K airT tasAdjust tair air TA (C)
air_pressure Pa air_pressure PRESS (KPa)
mole_fraction_of_carbon_dioxide_in_air mol/mol CO2
relative_humidity % relative_humidity rhurs NA rhum RH
surface_downwelling_photosynthetic_photon_flux_in_air mol m-2 s-1 PAR PAR (NOT DONE)
precipitation_flux kg m-2 s-1 cccc prAdjust rain acpc PREC (mm/s)
degrees wind_direction WD
wind_speed m/s Wspd WS
  • variable names are from MsTMIP.
  • standard_name is CF-convention standard names
  • units can be converted by udunits, so these can vary (e.g. the time denominator may change with time frequency of inputs)
  • soil moisture for the full column, rather than a layer, is soil_moisture_content

For example, in the MsTMIP-CRUNCEP data, the variable rain should be precipitation_rate. We want to standardize the units as well as part of the met2CF.<product> step. I believe we want to use the CF “canonical” units but retain the MsTMIP units any time CF is ambiguous about the units.

The key is to process each type of met data (site, reanalysis, forecast, climate scenario, etc) to the exact same standard. This way every operation after that (extract, gap fill, downscale, convert to a model, etc) will always have the exact same inputs. This will make everything else much simpler to code and allow us to avoid a lot of unnecessary data checking, tests, etc being repeated in every downstream function.

8.1.2 Using the API to get data

In order to access the data, we need to contruct a URL that links to where the data is located on Clowder. The data is then pulled down using the API, which “receives requests and sends responses” , for Clowder.

8.1.3 The structure of the Geostreams database

The meteorological data that is collected for the TERRA REF project is contained in multiple related tables, also know as a relational database. The first table contains data about the sensor that is collecting data. This is then linked to a stream table, which contains information about a datastream from the sensor. Sensors can have multiple datastreams. The actual weather data is in the third table, the datapoint table. A visual representation of this structure is shown below.

In this vignette, we will be using data from a weather station at the Maricopa Agricultural Center, with datapoints for the month of January 2017 from a certain sensor. These data are five minute summaries aggregated from observations taken every second.

8.1.4 Creating the URLs for all data table types

All URLs have the same beginning (https://terraref.ncsa.illinois.edu/clowder/api/geostreams), then additional information is added for each type of data table as shown below.

  • Station: /sensors/sensor_name=[name]
  • Sensor: /sensors/[sensor number]/streams
  • Datapoints: /datapoints?stream_id=[datapoints number]&since=[start date]&until=[end date]

A certain time period can be specified for the datapoints.

For example, below are the URLs for the particular data being used in this vignette. These can be pasted into a browser to see how the data is stored as text using JSON.

Possible sensor numbers for a station are found on the page for that station under “id:”, and then datapoints numbers are found on the sensor page under “stream_id:”.

The table belows lists the names of some stations that have available meteorological data and associated stream ids.

stream id name
3211 UA-MAC AZMET Weather Station - weather
3212 UA-MAC AZMET Weather Station - irrigation
46431 UA-MAC AZMET Weather Station - weather (5 min)
3208 EnvironmentLogger sensor_weather_station
3207 EnvironmentLogger sensor_par
748 EnvironmentLogger sensor_spectrum
3210 EnvironmentLogger sensor_co2
4806 UIUC Energy Farm SE
4807 UIUC Energy Farm CEN
4805 UIUC Energy Farm NE

Here is the json representation of a single five-minute observation:

[
   {
      "geometry":{
         "type":"Point",
         "coordinates":[
            33.0745666667,
            -111.9750833333,
            0
         ]
      },
      "start_time":"2016-08-30T00:06:24-07:00",
      "type":"Feature",
      "end_time":"2016-08-30T00:10:00-07:00",
      "properties":{
         "precipitation_rate":0.0,
         "wind_speed":1.6207870370370374,
         "surface_downwelling_shortwave_flux_in_air":0.0,
         "northward_wind":0.07488770951583902,
         "relative_humidity":26.18560185185185,
         "air_temperature":300.17606481481516,
         "eastward_wind":1.571286062845733,
         "surface_downwelling_photosynthetic_photon_flux_in_air":0.0
      }
   },

8.1.5 Querying weather sensor data stream

The data represent 5 minute summaries aggregated from 1/s observations.

8.1.6 Download data using the command line

Data can be downloaded from Clowder using the command line program Curl. If the following is typed into the commmand line, it will download the datapoints data that we’re interested in as a file which we have chosen to call spectra.json.

8.1.6.1 Using R

The following code sets the defaults for showing R code.

And this is how you can access the same data in R. This uses the jsonlite R package and desired URL to pull the data in. The data is in a dataframe with two nested dataframes, called properties and geometries.

The geometries dataframe is then pulled out from these data, which contains the datapoints from this stream. This is combined with a transformed version of the end of the time period from the stream.

8.2 Weather Plots

Create time series plot for one of the eight variables, wind speed, in the newly created dataframe.

8.2.1 High resolution data (1/s) + spectroradiometer

This higher resolution weather data can be used for VNIR calibration, for example. But at 1/s it is very large!

8.2.1.2 Download netCDF 1/s data from Clowder