Satellite-based estimates of photosynthetically active radiation for tropical ecosystems in Ghana-West Africa

Photosynthetically active radiation (PAR; 0.40-0.70 mu m) is a key driver in ecosystem biochemical processes, and thus a critical factor in agriculture productivity, ecosystem-atmosphere energy, and CO2 fluxes. There is however a dearth of PAR measurements in many regions. Therefore, this paper proposed to estimate and analyze the spatiotemporal distribution characteristics of PAR on zonal and seasonal scales at 22 sites representing four different tropical ecosystems (savannah, transition, forest, and coastal) in Ghana, using long-term sunshine duration measurements and satellite-based climatological reanalysis datasets spanning 1981-2010. It is shown that a generalized factor of 0.45, which varies between 0.40 and 0.60 annually, estimated PAR to a good approximation for all selected sites, with indices of agreement between 0.94 and 0.99. The satellite and estimated PAR have a mean low of 7.90 +/- 0.50 and 7.37 +/- 0.70 MJm(-2) day(-1) during the June-July-August season respectively, and a mean high of 8.90 +/- 0.43 and 9.10 +/- 0.40 MJm(-2) day(-1) during the March-April-May season respectively, largely associated with seasonal atmospheric conditions owing to dust and water vapor. The mean residual error in PAR estimation is 0.01 +/- 0.36 with the most seasonal variations in the dry and wet seasons. The study provides theoretical and practical insights for forest management and ecosystem preservation over the sub-region.

Automated summary

This study proposed a method to estimate and analyze the spatiotemporal distribution characteristics of PAR in different tropical ecosystems in Ghana, showing good approximation for all selected sites. The study also analyzed the seasonal variations of PAR, providing theoretical and practical insights for forest management and ecosystem preservation.