Abstract
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 400–1400 μmol m−2 s−1 was estimated with a mean bias error = 5.01 μmol m−2 s−1 (R2 = 0.87), providing a source of accurate data for high resolution models of gross primary productivity.
Highlights
The amount of photosynthetically active radiation (PAR) reaching the Earth’s surface is important because it is one of the key factors driving plant productivity and the production and storage of organic carbon [1]
A review of the literature suggested that PAR in photosynthetic photon flux density (PPFD) units is typically twice that of solar irradiance measured in energy units (W m-2), and that this conversion factor could be sensitive to atmospheric conditions
Data from the PAR sensor and pyranometer co-located at the Chilbolton Facility for Atmospheric and Radio Research (CFARR) between April 2011 and February 2012 are shown in figure 2
Summary
The amount of photosynthetically active radiation (PAR) reaching the Earth’s surface is important because it is one of the key factors driving plant productivity and the production and storage of organic carbon [1]. Satellite remote sensing was identified as a possible method to measure downwelling irradiance in the 1960s [2], and various methods have been developed since [3]. The same approaches have been used to estimate downwelling PAR, taking into account the narrower range of wavelengths compared with broadband irradiance [46]. Most of these methods aim to estimate the average PAR over daily or monthly periods, but for many purposes, such as plant productivity modelling in environments with rapidly changing cloud cover, finer temporal resolution is required. Janjai and Wattan [7] developed such a method for Thailand, but applying their method to the UK is more challenging because mid-latitude
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: IOP Conference Series: Earth and Environmental Science
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
