Seasonal and altitude dependence of thermospheric metastable helium densities measured by fluorescence lidar: lidar dataset

These are NetCDF files containing lidar return data from the helium fluorescence lidar described in the referenced paper (doi to be added). The data contain the following variables:

The data have one of two possible formats. For files beginning '2023', the instrument was operated in single frequency mode, and the files contain the following fields:

 'photons_chX' with X between 0 and 11 - A Nx3000 array of detected photon counts binned into N 10-second intervals in time and 3000 2-km bins in altitude. Note that only the first 1000 bins in the second axis contain data, up to an altitude of 2000 km; the arrays are then padded with zeros.

 'shots_chX' with X between 0 and 11 - An array of length N with the number of laser pulses fired during the corresponding interval.

 'time_offset' - A single value, giving the unix timestamp relative to which the 'time' variable is measured.

'time' - An array of length N with the midpoint time in milliseconds of the corresponding interval, measured relative to the 'time_offset'.

'altitude' - An array of length 3000 with the lower edges of the corresponding altitude bins, in meters.

For files beginning '2024', the instrument was operated in multi-frequency mode, and the files contain the following fields:

'photons_chX' with X between 0 and 11 - A 41xNx3000 array of detected photon counts binned into 41 1-pm bins in wavelength, N 10-s intervals in time, and 3000 2-km bins in altitude. Note that only the first 600 bins in the third axis contain data, up to an altitude of 1200 km; the arrays are then padded with zeros.

 'shots_chX' with X between 0 and 11 - A 41xN array with the number of laser pulses fired with the corresponding wavelength during the corresponding interval.

'wavelength' - An array of length 41 giving the central wavelength of each wavelength bin.

 'time_offset' - A single value, giving the unix timestamp relative to which the 'time' variable is measured.

'time' - An array of length N with the midpoint time in milliseconds of the corresponding interval, measured relative to the 'time_offset'.

'altitude' - An array of length 3000 with the lower edges of the corresponding altitude bins, in meters.

Note that this is a standardized data format used by many instruments; it contains several other variable fields that are not used by the present instrument and are therefore omitted from this description.