Design of a Solar Scintillometer

A solar scintillometer is an effective instrument to estimate seeing values of near-ground atmosphere. Measuring the scintillation effect of sunlight reaching ground can be used to estimate the size of near-ground turbulence elements in the light path. A solar scintillometer is just based on this principle. This paper describes hardwares and softwares of a solar scintillometer made by us, and presents preliminary observational results.Measurement of night seeing can use the scintillation effect of stars. But the sun which is observed in a daytime seeing measurement is an extended source and the scintillation effect of sunlight is an averaged result of many independent sub-sources. It is generally acknowledged that the scintillation effect of the sun is smoothed by the atmosphere at all heights and is not easy to be measured. Professor J.Beckers and his colleagues of the U.S.National Solar Observatory used a simple device to achieve the measurement of the solar scintillation effect. Having understood the working principle of their device and using references abroad, we modified their design and made a solar scintillometer. We have some preliminary experimental results for this device.Our design approach is based on using a photodiode and a current-voltage conversion circuit to receive sunlight signals as voltage signals. An active filter subsequently separates AC component and DC component from the voltage signals. Through a channel selector these two components are output to an analog-to-digital convertor. The results are collected by a microcontroller and sent to the host computer via a serial port. Using the output we can make appropriate data processing to achieve the measurment. A prototype designed according to this principle has been experimented in the Fuxian solar observing station of the Yunan Observatory. The experiments show that our design meets the requirement for estimating near-ground atmospheric seeing.Solar scintillometers are commonly used in solar site surveys. Based on actual usage in the coming days, our design can be improved and perfected.