| Popis: |
Now, active research is being carried out to separate direct and diffuse solar irradiance from the global horizontal irradiance. To fully determine these components, it is necessary to simultaneously use several instruments in such measurements, which include unshaded and shaded pyranometers, and an actinometer. One solution for these measurements is to eliminate the shaded pyranometer and actinometer. In this case, only an unshaded pyranometer will be involved in the measurements, and cumulus clouds will act as a natural shading screen. One important feature of cumulus clouds is their high optical density, as well as the presence of clear sky patches between individual clouds. This feature makes it possible to determine both a completely open solar disk and a completely closed one during the movement of clouds. An unshaded pyranometer receives a time series consisting mainly of measured Q of diffuse and direct radiation. With this time series of global horizontal irradiance, a variational analysis is carried out, according to the results of which Q are determined, at which the moment of the presence of cumulus clouds is detected, and the stability of the state of such points is additionally assessed. The presence of cumulus clouds leads to the formation of a very heterogeneous time series. We will use this feature in the analysis of a series of global horizontal irradiance, which will allow us to determine the presence of cumulus clouds automatically almost in real time. In the proposed method for detecting cumulus clouds, the previously proposed approach is used, which makes it possible to abandon the use of the clear-sky model. This approach makes it possible to reduce the length of the series for analysis to a 21-minute moving window, in which a search is made for inhomogeneous intervals in the global horizontal irradiance time series with V21≥0.33. Also, differences can be found by analyzing the series for a 3-minute window (±1 minute near the analyzed point), which moves within a 21-minute sample, according to the condition V3≥0.33. To check the facts of the presence of cumulus cloudiness, the results of the described detection algorithm were compared according to the global horizontal irradiance data for the warm period (May–September 2020). As a series of global horizontal irradiance, we took a continuous series of measurements from the CM-11 pyranometer (Kipp & Zonen, Netherlands) of the geophysical observatory of the IMCES SB RAS (Tomsk). The detection results were verified using visual control by color panoramic images of the All sky camera close to the pyranometer. In addition, one-hour visual observations of the state of the sky were used. |
