Via the reflection of incoming solar radiation and the creation of cloud droplets that act as cloud condensation nuclei, aerosols play a critical role in the Earth’s radiation budget. Aerosol optical properties in the troposphere, especially their behaviour near the ground level, are still poorly understood, making precise evaluation of their effect difficult. While a sunphotometer can measure aerosol optical thickness, it is only useful during the day and in near-cloudless conditions. A visibility metre, on the other hand, can have a value for visibility but can only work at a single wavelength, such as 875 nm. We suggest using a four-color light emitting diode (LED) source emitting at 455, 530, 590, and 625 nm as a light source for the long-path measurement of aerosol extinction to achieve multi-wavelength detection of aerosol extinction coefficient near the surface level. Within Chiba University’s campus, a near-horizontal light path with a round-trip distance of around 630 metres has been created. A 130 mm diameter telescope collimates the light beam, and a 200 mm diameter telescope attached to a photodiode detects the reflected beam from a retro-reflector. The LED source is modulated with a sinusoidal wave, and the modulated signal amplitude is detected and registered using a digital oscilloscope (Iwatsu, DS-5614A). The findings of the recent observation are compared to records from a visibility metre (Vaisala, PWD52) and a nephelometer (TSI3563) that can calculate the aerosol scattering coefficient.
Author (s) Details
Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Jenderal Soedirman, Jl. dr. Suparno 61, Grendeng-Purwokerto, Jawa Tengah, 53122, Indonesia.
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