Estimation of daily-integrated PAR from sparse satellite observations: comparison of temporal scaling methods

Abstract

Incident Photosynthetically Active Radiation (PAR) is a critical parameter for modelling ecosystem productivity. An algorithm for estimating instantaneous PAR from Moderate Resolution Imaging Spectroradiometer (MODIS) data was developed earlier; however, daily-integrated PAR is more meaningful than instantaneous PAR in many cases because many land surface models require a daily or coarser temporal resolution. This paper compares two different algorithms (adjusted sinusoidal interpolation and look-up table) for estimating daily-integrated PAR from instantaneous PAR values. Statistical analysis of the validation results indicates that the look-up table method more accurately estimates daily-integrated PAR than the use of adjusted sinusoidal interpolation. We also investigated how window size, daytime length and the number of overpass counts per day affect bias and the relative error of estimation. Validation using field measurements, and comparison with the Geostationary Operational Environmental Satellites PAR product, demonstrates that data collected by MODIS can be used to provide reliable estimates of daily-integrated PAR.

Acknowledgments

The authors thank the AmeriFlux network team and the investigators at the 11 stations used in this paper for providing in situ PAR measurements. The authors also thank two anonymous reviewers for their comments and suggestions. This work was financially supported by grants from the National Aeronautics and Space Administration (NAG512892 and NNG05GD10G). Ronggao Liu is supported in part by the National Natural Science Foundation from China (40471098).