Statically mounted polarsondes at Davis Station 2018/19

Full description

This dataset comprises measurements of backscatter intensity from two polarimetric backscatter sondes mounted statically at Davis Station, between December 2018 and October 2019.
One is located on a platform, about 1.8 m above ground, 15 m to the north of the Meteorology building, and facing approximately south west. The platform is the same as that on which many instruments associated with project AAS 4292 were mounted.
The other is mounted on a rail on the edge of the roof of the Climate Processes and Change building, near the eastern corner, facing southeast at about 6 m above ground.

The instruments emit polarised light (470 nm wavelength) horizontally into the atmosphere.

Each has two channels, with different polarisations. Each channel has two photodetectors, one with the analyser polariser oriented parallel to the emitted polarisation, and the other with analyser oriented perpendicular.

Meteorology building: Channel 1, vertically polarised light emitted; Channel 2, emitted light polarised 45 degrees to horizontal. Scattering plane horizontal.

Climate Processes and Change building: Channel 1, horizontally polarised light emitted; Channel 2, emitted light polarised 45 degrees to horizontal. Scattering plane vertical.

The data are in ASCII text format, recorded once per second and written to hourly log files. Each day at 0000Z these are archived to a compressed file (tar + gzip), with the date (UTC) of the compressed file creation being included in the filename of the gz file. A quirk of the timing is that a second or two of data from the start of the day are included with the data for the previous day. Also a few seconds of data are generally not recorded at the start of each day due to the computational overhead of the archiving process. An example line is 2017/03/05 01:59:46 t, 4598358, L, 0.12814012, 0.05185896, 0.40470508, 99.6, C, 0.08772506, 0.06333281, 1.38514388, 99.0, B, 9.0 The data are as follows; Date and time (UTC), "t", seconds elapsed, "L" (channel 1), co-polarised signal, cross-polarised signal, channel 1 depol, LED current (mA), "C" (channel 2), co-polarised signal, cross-polarised signal, channel 1 depol, LED current (mA), "B" (power supply), supply voltage. (Co- and cross-polarised are with respect to the emitted polarisation, not horizontal or vertical orientations.)

Lineage

Progress Code: completed

Statement: The presence of windows on the instruments, with varying levels of cleanliness, means that there is a variable background which must be judged on the basis of separate evidence of a precipitation event (incl. blizzards).

Notes

Purpose
The data were collected to give information on the shape of atmospheric scatterers in the emitted beam. If the emitted polarisation is perpendicular to the scattering plane, spherical scatterers give very little signal in the cross-polarised signal compared to the co-polarised, whereas nonspherical scatterers give substantial cross-polarised signal to varying degrees, depending on the details of the shape. If the emitted polarisation is oriented at 45° to the scattering plane all shapes of scatterers give substantial co- and cross-polarised signals.