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.

from openghg.tutorial import 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 Weybourne (WAO). The function will first check for any data from WAO 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.

from openghg.retrieve.icos import retrieve_atmospheric
wao_data = retrieve_atmospheric(site="WAO", species="ch4")

Now we can inspect wao_data, an ObsData object to see what was retrieved.


We can see that we’ve retrieved ch4 data that covers 2013-04-01 - 2015-07-31. Quite a lot of metadata is saved during the retrieval process, including where the data was retrieved from (dobj_pid in the metadata), the instruments and 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

metadata = wao_data.metadata
instrument_data = metadata["instrument_data"]
citation_string = metadata["citation_string"]

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


And we can easily get the citation string for the data


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 version of this notebook.


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 WAO.

wao_data_level1 = retrieve_atmospheric(site="WAO", species="CH4", data_level=1)

You can see that we’ve now got data from 2021-07-01 - 2022-04-24. The ability to retrieve different level data has been added for convenienve, choose the best option for your workflow.

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

wao_data_level1.plot_timeseries(title="WAO - 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.

new_data = retrieve_atmospheric(site="WAO", species="CH4", data_level=1, force_retrieval=True)

Here you may notice we get a message telling us there is no new data to process, if you force a retrieval and there is no newer data you’ll see this message.

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.

from openghg.retrieve.ceda import retrieve_surface
url = ""
hfd_data = retrieve_surface(url=url)

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


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.

hfd_data2 = retrieve_surface(site="hfd", species="co2")

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.

from openghg.tutorial import clear_tutorial_store