Data from different networks are heterogeneous, thus, the measurements are not standardized. Among other things, there are different soil moisture definitions (e.g. volumetric, water depth, mass, Soil Moisture Index, plant available water), different installation depths and different installation positions (vertical, horizontal), which specify if soil moisture is measured at a specific depth or over the interval. Therefore, datasets provided by participating networks are harmonized in time and with respect to the measurement units.
The ISMN harmonizes its data files into two standardized download formats (CEOP and "header+values"). More information about the formats could be found in Download formats section.
Observation datasets, which are available at sampling rates lower than hourly, have been thinned selecting the individual measurements at the hourly UTC reference time step or the one that is closest in time. No measurement available at this hourly sampling interval will get the value “NaN” (Not a Number). If the measurement value is outside a plausible range, its database entry will be labeled with a quality ﬂag.
All measurements provided to the ISMN concerning the soil moisture variable are stored in the database as fractional volumetric soil moisture (m³/m³) which is the most commonly used unit. Other variables' units are also harmonized to standard units.
All measurements are converted to Coordinated Universal Time (UTC).