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This will copy all the examples into your metview home folder. Soon you will see a folder called 'odb_seminar_2017' appear on your main Metview desktop. Double-click to enter it. You should see the following contents:
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ODB
This exercise shows how to retrieve ODB data from MARS, examine its structure, compute the differences between fields and visualise the data in various ways.
Enter folder 'basic'.
Retrieving the ODB data from MARS
The 'ret_temp' MARS Retrieval icon is already prepared for you to fetch Land TEMP ODB data from MARS fro a given date. Edit the icon (right-click & edit) and see what parameters are set. The most important ones are as follows:
| Parameter | Value | Notes |
|---|---|---|
| Type | MFB | Mondb feedback |
| Obsgroup | 17 | Conventional |
| Reportype | 16022 | land TEMP |
Close the icon editor and perform the data retrieval by choosing execute from the icon's context menu. The icon name should turn orange whilst the retrieval takes place, then green to indicate success. The data is now cached locally. To see what was retrieved, right-click examine the icon. This brings up Metview's ODB Examiner tool. Here we can see the metadata (Columns tab) and the actual data values themselves as well (Data tab). Close the ODB Examiner.
To save the ODB data from the cache to disk, right-click Save result on the Mars Retrieval icon and save as 'temp.odb'. A few seconds later an ODB Database icon with the given name will appear in your folder.
Using the ODB Visualiser
We will visualise the 500 hPa temperature values from this ODB using the 'vis_temp' ODB Visualiser icon. The query we need to perform is as follows:
| Code Block | ||
|---|---|---|
| ||
select
lat@hdr,
lon@hd,
obsvalue@body
where
varno = 2 and vertco_reference_1=50000 |
Now edit the 'vis_temp' icon.
First, drop your ODB Database icon into the ODB Data field.
Next, specify the where statement of the query in the ODB Where parameter as:
| Code Block |
|---|
varno = 2 and vertco_reference_1=50000 |
Save these settings by clicking the Save button at the bottom-right of the icon editor (or click Ok to save and close the editor).
Right-click visualise the icon to generate the plot. Then drag the the provided Symbol Plotting, Coastlines, Legend and Text Plotting icons into the plot. Having done so you should see something like this.
Inspecting the Data Values in the Plot
Data values at the cursor position can be inspected with the Cursor Data Tool, which can be activated by pressing on the gun-sight icon in the toolbar of the Display Window. The Cursor Data Tool displays the co-ordinates of the current cursor position and the information for the nearest data point to this position.
You may find hard to use the Cursor Data Tool for ODB since it is complicated to properly position the cursor in data dense regions in the plot. To overcome this difficulty you need to launch the Magnifier by pressing on the magnifier icon in the toolbar and navigate it to your area of interest in the plot.
Now if you move the cursor inside the magnifying glass it is significantly easier to distinguish the individual data points since you navigate the cursor inside a closed-up region.
Explore the the plot
In the plot window activate the cursor data and try to inspect the actual data values. Next, enable the sidebar and select the Data tab. Here you have metadat
data:
This panel shows all the plotted data values in a list. In the bottom-left corner click on the button to activate the data probe. The probe is synchronised with the list. Try to drag it around in the plot, or change its position through the list.
Using marcro.
Enter folder 'radiance_map'. The ODB database "ASMUA.odb" stores AMSU-A brightness temperature observations. Right-click examine to start up the ODB examiner and study the Columns and Data tabs in it.
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