Dimensions

Main dimensions

The following dimensions are present in every EBAS NetCDF file:

time: time dimension for measurement data

metadata_time: time dimension for metadata

tbnds: addirional dimension for :ref:time boundary variables<time_bnds>

For each data variable, there will be a dimension for the different flags used in the flag variable.

Additional dimensions for multidimensional variables

time

The time dimension represents the time ranges for all measurements in the time series of all data variables.

All data variables share the same time dimension and thus contain the same measurement intervals.

The time variable is, following the CF convention defined as follows:

standard_name: time
long_name: time of measurement
units: days since 1900-01-01 00:00:00 UTC
axis: T
calendar: gregorian
bounds: time_bnds

Following the CF convention the time variable is defined with the standard name time and uses a supported unit specification. CF also requires the calendar attribute and recommends the bounds attribute. More on the Time boundaries can be found below.

metadata_time

The dimension metadata_time is used for Time depenendent EBAS metadata.

Time boundaries

The variables time and metadata_time associated with the main dimensions of the EBAS NetCDF files contain only timestamps (point in time).

In reality, measurements are performed over a certain time range (e.g. one hour). Thus, each measurement has a start and an end time.

The CF convention defines for this problem the concept of boundary variables.

The time axis values (in the time variable) are set to the midpoint of the time ranges for all measuremnts. The additional variable time_bnds contains one more dimension (tbnds, length 2) an thus specifies starttime and endtime of each measurement.

In analogy, the dimension variabl metadata_time contains a single timestamp (midtime) for each time range with a distinct set of metadata. The associated boundary variable metadata_time_bnds contains an additional dimension tbnds (length 2), which contains start- and end times for each metadata validity period.

Additional dimensions

Some parameters in EBAS have additional dimensions, the most prominent are:

Dimension	Description, applies to, example
Wavelength	For variable which are measured in multiple wavelength, e.g. aerosol_light_scattering_coefficient (nepehlometer), aerosol_absorption_coefficient (filter_absorption_photometer), aerosol_optical_depth (sun_tracking_filter_radiometer).
Wavelength min, Wavelength max	Same as above, but the wavelengths are specified as max and min, thus adding two additional dimenstions.
Wavelength 1, Wavelength 2	For aerosol_absorption_angstrom_exponent calculated between two wavenelgths.
D	Particle diameter (size bins), e.g, for particle_number_size_distribution.
Dmin, Dmax	Same as above, but the size bins are defined with an upper and lower size, thus adding two additional dimenstions.
Tower inlet height	Tower measurements performed in different heights.
Profile height	aerosol_extinction_coefficient (maxdoas)
RH, RH base, RH base max, RH humidified	aerosol_light_(back)scattering_coefficient as a function of rH.
SS	Supersaturaion (%), for cloud_condensation_nuclei_number_concentration
Location	Location of measurements, used for auxiliary data. E.g. temperature, pressure or humidity measured at different points in the sample line. E.g. temperature, Location=inlet; temperature, Location=instrument inlet; temperature, Location=instrument internal; temperature, Location=sheath air loop

Flag dimensions

Each data variable is accompanied by a variable containing flag information. This flag variable has the same dimensions as the measurement variable, plus one additional dimension (<variable name>_qc_flags) for the flags which are associated with each single measurement. The length of this additional dimension is equal the maximum number of flags attached to a single measurement in the file. More information on this in Flag variable.