Using digital image processing to characterize the Campbell–Stokes sunshine recorder and to derive high-temporal resolution direct solar irradiance

Abstract

Abstract. The Campbell-Stokes sunshine recorder (CSSR) has been one of the most commonly used instruments for measuring sunshine duration (SD) through the burn length of a given CSSR card. Many authors have used SD to obtain information about cloudiness and solar radiation (by using Ångström-Prescott type formulas), but the burn width has not been used systematically. In principle, the burn width increases for increasing direct beam irradiance. The aim of this research is to show the relationship between burn width and direct solar irradiance (DSI) and to prove whether this relationship depends on the type of CSSR and burning card. A method of analysis based on image processing of digital scanned images of burned cards is used. With this method, the temporal evolution of the burn width with 1 min resolution can be obtained. From this, SD is easily calculated and compared with the traditional (i.e., visual) determination. The method tends to slightly overestimate SD, but the thresholds that are used in the image processing could be adjusted to obtain an improved estimation. Regarding the burn width, experimental results show that there is a high correlation between two different models of CSSRs, as well as a strong relationship between burn widths and DSI at a hightemporal resolution. Thus, for example, hourly DSI may be estimated from the burn width with higher accuracy than based on burn length (for one of the CSSR, relative root mean squared error is 24 and 30 %, respectively; mean bias error is −0.6 and −30.0 W m −2 , respectively). The method offers a practical way to exploit long-term sets of CSSR cards to create long time series of DSI. Since DSI is affected by atmospheric aerosol content, CSSR records may also become a proxy measurement for turbidity and atmospheric aerosol loading.

Relationship between sunshine duration and temperature trends across Europe since the second half of the twentieth century

“…As we also use country averages which might dim possible problems in one station, we decided to take all available series. Some countries have changed from traditional manual instruments (such as Campbell-Stokes and Jordan heliographs) to automatic electronic recorders since the 1980s, which produce readings that are not identical and can introduce inhomogeneities in the time series [e.g., Kerr and Tabony, 2004;Legg, 2014;Matuszko, 2015;Sanchez-Romero et al, 2015;Stanhill and Cohen, 2008]. Over Europe, the Campbell-Stokes recorders still dominate in the climatological network [e.g., Sanchez-Lorenzo et al, 2007Legg, 2014], and in some of the countries with documented changes in the instruments, such as Switzerland (at the end of the 1970s and early 1980s) and the Netherlands (early 1990s), the influence of it are reported to be minor [Sanchez-Lorenzo and Wild, 2012;Hinssen and Knap, 2007].…”

Is the summer season losing potential for solar energy applications in South Africa?

“…The long-term SD dataset is required for trend analysis studies. The Campbell-Stokes sunshine recorder, invented in the late nineteenth century (Sanchez-Romero et al, 2015), was the only instrument that SAWS used to measure the sunshine.…”

“…The network for measuring the duration of sunshine is, however, dense compared with GHI, DNI and DHI. There are long established sunshine duration (SD) measurement activities across the world (Sanchez-Romero et al, 2015). The data availability for SD is also better than for GHI, DNI and DHI in South Africa because simpler and less expensive instruments are used for measuring it.…”

A Deep Learning Model for Striae Identification in End Images of Float Glass

“…Thus, the logarithmic loss function, i.e. binary cross entropy function, was adopted as the objective function [30]. For the binary classification problem, there are two possible categories for each image.…”