Submitted to: International Journal of Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2006
Publication Date: 1/15/2007
Citation: Houberg, R., Henrik, S., Emmerich, W.E., Moran, M.S. 2007. Inferences of all-sky solar irradiance using Terra and Agua MODIS satellite data. International J. of Remote Sensing. 28(20): 4509-4535.
Interpretive Summary: Solar radiation is the driving force for the world energy and carbon dioxide budgets. Being able to estimate solar radiation continuously at all point on the earth surface will greatly increase our ability to understand climate and associated climate change. Presently we have estimates from individual measurement points. This work was able to take satellite remote sensing data that is available for entire earth surface and through modeling make close estimates to the actual measurements made for solar radiation at many locations in southern Arizona. This result will be of great benefit to scientist studying climate to allow for much better climatic models and to make better predictions of climate change. Society will benefit from knowing how climate is going to change and being able to make decisions on adjustments to coming climate change.
Technical Abstract: Solar irradiance is a key environmental control and accurate spatial and temporal solar irradiance data are important for a wide range of applications related to energy and carbon cycling, weather prediction and climate change. This study presents a satellite-based scheme for the retrieval of all-sky solar irradiance components that links a physically based clear-sky model with a neural network version of a rigorous radiative transfer model. The scheme exploits the improved cloud characterization and retrieval capabilities of the MODIS instrument onboard the Terra and satellites, and employs a cloud motion tracking scheme for the production of hourly solar irradiance data throughout the day. The scheme was implemented for the Island of Zealand, Denmark (56° N, 12° E) and Southern Arizona, USA (31° N, 110° W) permitting model evaluation for two highly contrasting climates and cloud environments. Information on the atmospheric state was provided by MODIS data products and verifications against Aerosol Robotic Network (AERONET) data demonstrated usefulness of MODIS aerosol optical depth and total precipitable water vapor retrievals for the delineation of spatial gradients. However aerosol retrievals were significantly biased for the semi-arid region and water vapor retrievals were characterized by systematic deviations from the measurements. Hourly global solar irradiance data were retrieved with overall root mean square deviations of 11.5 % (60 W m-2) and 26.6 % (72 W m-2) for Southern Arizona and the Island of Zealand, respectively and for both regions hourly satellite estimates were shown to be more reliable than pyranometer measurements from ground stations only 15 km away from the point of interest, which is comparable to the accuracy level obtainable from geostationary satellites with image acquisitions every 15 – 30 minute. The proposed scheme is particularly useful for solar irradiance mapping in high-latitude regions as data from geostationary satellites experience a gradual degradation in spatial resolution and overall quality with latitude and become unusable above approximately 60° latitude. However, in principle the scheme can be applied anywhere on the globe and a synergistic use of MODIS and geostationary satellite datasets may be envisaged for some applications.