Block matching algorithms: Their applications and limitations in solar irradiance forecasting

Block matching algorithms (BMAs) are widely used in motion analyses of 2D image data. Comparisons are made between one subregion and all adjacent subregions at consecutive timesteps to seek the the most likely 2D evolution of the subregion using the minimisation of various cost functions such as cross-correlation coefficient, sum of the absolute value of difference and sum of squared difference. BMAs are based on the assumption that the inter-frame motion is small. Therefore, in situations where high spatial and temporal resolution irradiance data is used, the algorithms can generate motion vectors describing the changes in irradiance maps and cloud images. We demonstrate the application of BMAs to irradiance map forecasting using global horizontal irradiance data collected from 10 Singapore meteorological stations. We then discuss the application of BMAs in cloud forecasts, which can as well be used for radiation assessment. We also propose a cloud boundary tracking method used in situations where the cloud image has low spatial resolution. The proposed algorithms act as a preliminary step to achieve high-accuracy 2D solar irradiance forecasts.