Simulation of short-wave solar radiative transfer across a roadway embankment

Abstract

Permafrost under a roadway embankment is sensitive to temperature increments. Thermal stability of the underlying permafrost is mainly regulated by the solar absorption at the embankment surface. Multiple reflections between the embankment’s side slope and its adjacent ground surface may increase the solar absorption of the embankment but have not been studied. Here we model the short-wave radiative transfer across an embankment and then compare the simulated reflectivity against the measured reflectivity of an embankment prototype at a clear weather. It is found that the solar absorption of the embankment is complexly and simultaneously influenced by the solar position, the embankment configuration, the sky clearness factors, and others. We do not exhaust these influences but focus on the absorptivity of the ground and of the side slope due to the solar trapping effect. It is found that the solar trapping effect increases the absorptivity of the side slope about 0–0.03 for a common embankment with a typical surface absorptivity of 0.80. This small difference implies that despite the solar trapping effect of the side slope, increasing the side slope reflectivity reduces the slope’s solar absorption effectively.Permafrost under a roadway embankment is sensitive to temperature increments. Thermal stability of the underlying permafrost is mainly regulated by the solar absorption at the embankment surface. Multiple reflections between the embankment’s side slope and its adjacent ground surface may increase the solar absorption of the embankment but have not been studied. Here we model the short-wave radiative transfer across an embankment and then compare the simulated reflectivity against the measured reflectivity of an embankment prototype at a clear weather. It is found that the solar absorption of the embankment is complexly and simultaneously influenced by the solar position, the embankment configuration, the sky clearness factors, and others. We do not exhaust these influences but focus on the absorptivity of the ground and of the side slope due to the solar trapping effect. It is found that the solar trapping effect increases the absorptivity of the side slope about 0–0.03 for a common embankment with a typical surface absorptivity of 0.80. This small difference implies that despite the solar trapping effect of the side slope, increasing the side slope reflectivity reduces the slope’s solar absorption effectively.