# Advances in Simulating Radiative Transfer in Complex Environments
## 3 Results and Discussion  
To give an overview on the differences between AVF and IVS, visualizations of the case study simulation results are presented. Radiation patterns as well as temperature distributions and impacts on thermal comfort are compared using absolute value maps of both scenarios to evaluate the advancements provided by the new IVS scheme. After the theoretical explanations in Section 2.2, principles in IVS modeling are visually demonstrated by the 3D view of the model area. Figure 4 shows the rays that were traced for one specific grid cell at 138, 150, 6 amid the center of Columbus Circle. Each ray represents a view sphere segment of the grid cell to be analyzed. It is emitted from the grid cell center and searches for objects in each view sphere direction. When a building or soil surface is hit, the raytracing is aborted, and the object information is stored. With increasing height angle and especially above the highest object height, the length of each raytracing segment is, to save computational time, drastically increased as the probability of hitting an object is diminishing. \begin{table}
\begin{tabular}{c c} \hline \hline
**General Properties of Both Simulations** & \\ \hline Start Date and Time (Local) & 21.07.2017 05:00 \\ Duration [h] & 24 \\ Wind Speed [m s\({}^{-1}\)] & 2 \\ Wind Direction [\({}^{\circ}\)] & 325 \\ Meteorological Boundary Conditions & Full Forcing \\ Location Lat (Lower Left Corner) & 40.76\({}^{\circ}\) N \\ Location Lon (Lower Left Corner) & \(-\)73.98\({}^{\circ}\) E \\ Dimensions & 360 \(\times\) 260 \(\times\) 52 \\ Resolutions (X, Y, Z) [m] & 2.5 \(\times\) 2.5 \(\times\) 5 \\ Lowest Grid Cell Split & Yes \\ Telescoping: Factor and Starting Height & 30\% above 180 m \\ Height of 3D Model Domain [m] & 1434 m \\ Building Indoor Temperature Held Constant at & 20 \({}^{\circ}\)C \\ View Factor Update Interval & 30 days \\ \hline
**Specific Radiation Scheme Settings for IVS Simulation** & \\ \hline Height Angle High Resolution Near Ground & 15\({}^{\circ}\) \\ Azimuthal Angle High Resolution Near Ground & 15\({}^{\circ}\) \\ Height Angle Low Resolution Above Height Boundary & 30\({}^{\circ}\) \\ Azimuthal Angle Low Above Height Boundary & 30\({}^{\circ}\) \\ Height Boundary between High and Low Resolution & 8 m \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of the proof-of-concept simulations. Figure 4: This specifically generated simulation output depicts the length of raytracing segments for one observed grid cell above the center of Columbus Circle. The 3D output view shows these raytracing lengths from a far perspective demonstrating the long ray distance and the length increase with height in (**a**) and from a nearby perspective with a 50 % decreased data cube size, 50 % data cube transparency, and data being filtered for height levels below k = 13 to visualize the high view sphere resolution and the resulting rays near the observed cell in (**b**). ENVI-met provides multiple output variables to allow the analysis of radiation patterns. Variables containing shortwave or longwave radiation values are distinguished between the upper and lower hemispheres to allow for a specification from which direction the radiation is received. Analyzing, for example, longwave radiation distribution received from the lower hemisphere in a horizontal cut at 1.5 m height, most radiation input probably originates from soil surfaces, ground vegetation, and nearby facade elements. Figure 5a demonstrates that longwave radiation values cover a wider range and more distinct differences over the model at 13:00 in the IVS scenario compared against the AVF scenario. Especially the pattern of park streets can be recognized, as they emit more longwave radiation than their surroundings. That is caused by their low-albedo surfaces that heated up more during the morning hours in contrast to the street canyons, which have been shaded by buildings.