Point Observations¶

METplus can work with point observations in several formats, with converters available to MET’s internal netcdf based format.

Point observation conversion happens in the metplus_prep_obs and metplus_ascii2nc tasks. After point observations have been converted they are used by metplus_point_stat to create statistics.

ODB2¶

ODB2 format data is first converted to MET ASCII format and then to MET point nc format. The pyodc library is required to do this.

To enable generic ODB2 format conversion add the opt flag odb2 to the task metplus_prep_obs.

ODB2 data will be read from files matching $CUSTOM_ODB2_PATTERN. This pattern can contain strftime-style placeholders, which are replaced with the observation valid time, and shell globs. ODB2 data with .gz, .bz2 or .zst extensions will be automatically decompressed before reading.

Valid times to read data can be set in $OBS_TIMES. This should be an ISO time recurrence pattern, e.g. R12/$CYLC_TASK_CYCLE_POINT/PT1H to read 12 times one hour apart starting from the current cycle point. The Jinja2 filter duration_as is useful when creating the recurrence.

The ODB2 fields are mapped to MET ASCII columns like:

ASCII Columns¶
Index	Field	Description	point_stat config
0	Message_Type	uses PrepBUFR names where known, otherwise the ODB `reportype@hdr` value.	`POINT_STAT_MESSAGE_TYPE`
1	Station_ID	`statid@hdr`
2	Valid_Time	`date@hdr_time@hdr`
3	Lat	`lat@hdr`
4	Lon	`lon@hdr`
5	Elevation	`stalt@hdr`
6	Variable_Name	uses ODB variable names from https://codes.ecmwf.int/odb/varno/	`OBS_VAR<n>_NAME`
7	Level	is the observation pressure level (where available).	`OBS_VAR<n>_LEVELS=P<level>`
8	Height	is 0 for surface observations.	`OBS_VAR<n>_LEVELS=Z0`
9	QC_String	not currently used	`POINT_STAT_OBS_QUALITY_EXC`, `POINT_STAT_OBS_QUALITY_INC`
10	Observation_Value	`obsvalue@body`

Basic QC is done on the ODB2 data before the conversion by checking that report_status@hdr and datum_status@body are both 1.

A sample runtime for reading ODB2 format data is:

[runtime]
    [[metplus_prep_fcst]]
        [[[environment]]]
            ROSE_APP_OPT_CONF_KEYS = "odb2"
            CUSTOM_ODB2_PATTERN = "/path/%Y%m%dT%H%MZ/obs.odb2.gz"
            {# Time separation between ODB2 files #}
            {% set ODB2_OBS_FREQ = "PT3H" %}
            {# Calculate the number of observations to read #}
            {% set ODB2_OBS_R = (
                    (ANALYSIS_LENGTH | duration_as('h')) /
                    (ODB2_OBS_FREQ | duration_as('h'))
                ) | int
            %}
            OBS_TIMES = R{{ODB2_OBS_R}}/$CYLC_TASK_CYCLE_POINT/{{ODB2_OBS_FREQ}}

Customising ODB2 data at different sites¶

If sites have a consistent path for their ODB2 data they can set up preset patterns, see app/metplus_prep_fcst/bin/prepBureauNCI.py for an example.