Add sensor height metadata
The height of measurement could be a useful information. This could be supported by adding for each MeteoData field a SensorHeight field: positive above ground, negative underground.
SMETIO could add a sensor_height vector in the header (like we already have units_offset). IMISIO could read this information from the database, GSNIO from the web service, SNIO would need it to be provided as an extra key in io.ini (key, vector pair).