Albedo Measurement System for UVA and the Visible Wavelength

Abstract

An instrument system to measure the UVA and visible albedo from the snow capped mountain ranges has been built. Albedo is the ratio between the incoming radiation and the reflected radiation for a given location. Measuring albedo of the UVA and the Photosynthetic Active Radiation (PAR) wavelength range involves measuring the global irradiance and the reflections from the slopes around the measuring location. This system can be installed in any mountain peak to measure the reflectivity around the snow covered slopes. Global irradiance is measured by a standard global sensor using a Gigahertz UVA head and a home built UVA head. The UVA reflection is measured by an 1° telescope fitted with a home built UVA head. The home built UVA detector systems have been built using Hamamatsu silicon UV diodes and temperature stabilized using Peltier elements driven by a closed loop feedback control system. Two such similar systems have been built and used for directional and global measurements for direct comparison. PAR reflection is measured by a standard area CCD camera fitted with a wide angle lens and an optical filter. Global PAR is measured by using LI-COR Quantum sensors. The telescope and the CCD camera have been mounted on an Alta-Azimuth mount for scanning the surface around the peak to measure the reflectivity. A set of reflection standards along with the global PAR sensor has been mounted on a boom and fixed with the azimuth table. These reflection standards are visible in the field of view of the CCD camera. This provides the reference pixels in every CCD image that can be used to calibrate the rest of the CCD pixels. This system has been used to make the albedo images at the Zugspitze for the CUVRA (Characteristic of Ultra Violet Radiation in the Alps) project. Preliminary results are shown here.