Retrieving data from remote archives#

This tutorial covers the retrieval of data from the ICOS Carbon Portal and the CEDA archives.

0. Using the tutorial object store#

To avoid adding the example data we use in this tutorial to your normal object store, we need to tell OpenGHG to use a separate sandboxed object store that we’ll call the tutorial store. To do this we use the use_tutorial_store function from openghg.tutorial. This sets the OPENGHG_TUT_STORE environment variable for this session and won’t affect your use of OpenGHG outside of this tutorial.

In [1]: from openghg.tutorial import use_tutorial_store

In [1]: use_tutorial_store()

1. ICOS#

It’s easy to retrieve atmospheric gas measurements from the ICOS Carbon Portal using OpenGHG. To do so we’ll use the retrieve_atmospheric function from openghg.retrieve.icos.

Checking available data#

You can find the stations available in ICOS using their map interface. Click on a site to see it’s information, then use it’s three letter site code to retrieve data. You can also use the search page to find available data at a given site.

Using `retrieve_atmospheric`#

First we’ll import retrieve_atmospheric from the retrieve submodule, then we’ll retrieve some data from Saclay (SAC). The function will first check for any data from SAC already stored in the object store, if any is found it is returned, otherwise it’ll retrieve the data from the ICOS Carbon Portal, this may take a bit longer.

In [1]: from openghg.retrieve.icos import retrieve_atmospheric

In [2]: sac_data = retrieve_atmospheric(site="SAC", species="ch4", sampling_height="100m")

In [3]: len(sac_data)

Here sac_data is a list of two ObsData objects, each one containing differing amounts of data. We can have a look at the reason for their being two versions of data by checking the dataset_source key in the attached metadata.

In [7]: dataset_sources = [obs.metadata["dataset_source"] for obs in sac_data]

In [8]: dataset_sources

Let’s say we want to look at the ICOS dataset, we can select that first dataset

In [9]: sac_data_icos = sac_data[0]

In [11]: sac_data_icos

We can see that we’ve retrieved ch4 data that covers 2021-07-01 - 2022-02-28. A lot of metadata is stored during the retrieval process, including where the data was retrieved from (dobj_pid in the metadata), the instruments, their associated metadata and a citation string.

You can see more information about the instruments by going to the link in the instrument_data section of the metadata

In [14]: metadata = sac_data_icos.metadata

In [15]: metadata["instrument_data"]

In [16]: metadata["citation_string"]

Here we get the instrument name and a link to the instrument data on the ICOS Carbon Portal.

Viewing the data#

As with any ObsData object we can quickly plot it to have a look.

NOTE: the plot created below may not show up on the online documentation. If you’re using an ipython console to run through the tutorial, the plot will open in a new browser window.

In [17]:  sac_data_icos.plot_timeseries()

Data levels#

Data available on the ICOS Carbon Portal is made available under three different levels (see docs).

- Data level 1: Near Real Time Data (NRT) or Internal Work data (IW).
- Data level 2: The final quality checked ICOS RI data set, published by the CFs,
                to be distributed through the Carbon Portal.
                This level is the ICOS-data product and free available for users.
- Data level 3: All kinds of elaborated products by scientific communities
                that rely on ICOS data products are called Level 3 data.

By default level 2 data is retrieved but this can be changed by passing data_level to retrieve_icos. Below we’ll retrieve some more recent data from SAC.

In [2]: sac_data_level1 = retrieve_atmospheric(site="SAC", species="CH4", sampling_height="100m", data_level=1, dataset_source="icos")

In [4]: sac_data_level1.data.time[0]

In [7]: sac_data_level1.data.time[-1]

You can see that we’ve now got quite recent data, usually up until a day or so before these docs were built. The ability to retrieve different level data has been added for convenience, choose the best option for your workflow.

NOTE: level 1 data may not have been quality checked.

In [10]: sac_data_level1.plot_timeseries(title="SAC - Level 1 data")

Forcing retrieval#

As ICOS data is cached by OpenGHG you may sometimes need to force a retrieval from the ICOS Carbon Portal.

If you retrieve data using retrieve_icos and notice that it does not return the most up to date data (compare the dates with those on the portal) you can force a retrieval using force_retrieval.

In [11]: new_data = retrieve_atmospheric(site="SAC", species="CH4", data_level=1, force_retrieval=True)

Here we get a message telling us there is no new data to process, this will depend on the rate at which datasets are updated on the ICOS Carbon Portal.

2. CEDA#

To retrieve data from CEDA you can use the retrieve_surface function from openghg.retrieve.ceda. This lets you pull down data from CEDA, process it and store it in the object store. Once the data has been stored successive calls will retrieve the data from the object store.

NOTE: For the moment only surface observations can be retrieved and it is expected that these are already in a NetCDF file. If you find a file that can’t be processed by the function please open an issue on GitHub and we’ll do our best to add support that file type.

To pull data from CEDA you’ll first need to find the URL of the data. To do this use the CEDA data browser and copy the link to the file (right click on the download button and click copy link / copy link address). You can then pass that URL to retrieve_surface, it will then download the data, do some standardisation and checks and store it in the object store.

We don’t currently support downloading restricted data that requires a login to access. If you’d find this useful please open an issue at the link given above.

Now we’re ready to retrieve the data.

In [1]: from openghg.retrieve.ceda import retrieve_surface

In [2]: url = "https://dap.ceda.ac.uk/badc/gauge/data/tower/heathfield/co2/100m/bristol-crds_heathfield_20130101_co2-100m.nc?download=1"

In [3]: hfd_data = retrieve_surface(url=url)

In [3]: hfd_data

Now we’ve got the data, we can use it as any other ObsData object, using data and metadata.

In [4]: hfd_data.plot_timeseries()

Within an ipython session the plot will be opened in a new window, in a notebook it will appear in the cell below.

Retrieving a second time#

The second time we (or another user) retrieves the data it will be pulled from the object store, this should be faster than retrieving from CEDA. To get the same data again use the site, species and inlet arguments.

In [6]: hfd_data_ceda = retrieve_surface(site="hfd", species="co2")

In [7]: hfd_data_ceda

3. Cleanup#

If you’re finished with the data in this tutorial you can cleanup the tutorial object store using the clear_tutorial_store function.

In [8]: from openghg.tutorial import clear_tutorial_store

In [9]: clear_tutorial_store()
INFO:openghg.tutorial:Tutorial store at /home/gareth/openghg_store/tutorial_store cleared.