Estimating hourly variation in photosynthetically active radiation across the UK using MSG SEVIRI data

The amount of photosynthetically active radiation (PAR) reaching the Earth’s surface is a key input variable in most gross primary productivity models. However, poor representation of PAR due to large pixel size or limited temporal sampling is one of the main sources of uncertainty in such models. This paper presents a method to estimate PAR at up to 1 km spatial resolution at a regional to global scale. The method uses broadband radiance data (400-1100nm) and per-pixel estimates of relative cloud cover from a geostationary satellite to estimate the amount of PAR reaching the Earth’s surface at high spatial and temporal resolution (1-2 km and hourly). The method was validated using data from 54 pyranometers located at sites across the UK. Hourly averaged PAR over the range 400-1400µmol m-2s-1 was estimated with a mean bias error = 5.01 µmol m-2s-1(R2= 0.87), providing a source of accurate data for high resolution models of gross primary productivity.