Submitted as: model description paper
08 Apr 2022
Submitted as: model description paper | 08 Apr 2022
Status: this preprint is currently under review for the journal GMD.

HORAYZON v1.1: An efficient and flexible ray-tracing algorithm to compute horizon and sky view factor

Christian R. Steger1, Benjamin Steger2, and Christoph Schär1 Christian R. Steger et al.
  • 1Institute for Atmospheric and Climate Sciences, ETH Zürich, Zürich, Switzerland
  • 2ESRI Research & Development Center Zürich, Zürich, Switzerland

Abstract. Terrain parameters like topographic horizon and sky view factor (SVF) are used in numerous fields and applications. In atmospheric and climate modelling, such parameters are utilized to parameterise the effect of terrain geometry on radiation exchanges between the surface and the atmosphere. Ideally, these parameters are derived from a high-resolution digital elevation model (DEM), because inferring them from coarser elevation data induces a smoothing effect. Computing topographic horizon with conventional algorithms is however slow, because large amounts of non-local terrain data have to be processes. We propose a new and more efficient method, which is based on a high-performance ray tracing library. By applying terrain simplification to remote topography, this allows the application of the new algorithms also with very high-resolution (< 5 m) DEM data, which otherwise would induce an excessive memory footprint. The topographic horizon algorithm is accompanied by a SVF algorithm, which was verified to work accurately for all terrain – even very steep and complex one. We compare the computational performance and accuracy of the new horizon algorithm with two reference methods from literature and illustrate its benefits. Finally, we illustrate how sub-grid SVF values can be efficiently computed with the newly derived horizon algorithm for a wide range of target grid resolutions (1–25 km).

Christian R. Steger et al.

Status: open (until 03 Jun 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2022-58', Laura Rontu, 01 May 2022 reply

Christian R. Steger et al.

Christian R. Steger et al.


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Short summary
Terrain horizon and sky view factor are crucial quantities for many geoscientific applications. E.g., they are used to account for effects of terrain on surface radiation in climate and land surface models. Because typical terrain horizon algorithms are inefficient for high-resolution (< 30 m) elevation data, we developed a new algorithm based on a ray-tracing library. A comparison with two conventional methods revealed both its high performance as well as its accuracy for complex terrain.