An improved GUI software for light obscuration sensors.

Light obscuration sensors are widely used for measuring the size distribution of insoluble mineral dust particles in ice core samples. They work on a flow-through basis: the sample is melted and pumped through a small cell transilluminated by a laser beam. When a microparticle intercepts the beam, a photodiode measures a decrease in the transmitted power and the optical extinction cross-section is obtained, thus the particle size retrieved. Such instruments are calibrated by means of reference spherical particles with refractive index 1.58, which leads to unavoidable systematic errors when determining the size of particles of different materials. In this contribution, we propose a reliable and consistent method to overcome this limitation by leaving the refractive index as a parameter to be set according to the sample composition. An ad hoc graphical interface has been developed to this purpose to drive an in-line instrument. We present results obtained from spheres of reference materials and compare them with an independent optical method. This method will improve the accuracy in ice core record characterization and reduce discrepancies between data obtained with different methods.