Calculating Topographic Exposure with ArcGIS Raster Calculator?

Decoding the Landscape: Calculating Topographic Exposure with ArcGIS Raster Calculator

Ever wonder why certain spots feel more exposed to the elements than others? It’s all about topographic exposure, or TOPEX as some folks call it. Think of it as a measure of how sheltered a location is, based on the lay of the land around it. Turns out, this seemingly simple idea has some pretty powerful applications.

So, what exactly is topographic exposure? Well, in a nutshell, it tells you how protected a site is by the surrounding hills and valleys. It’s not just about how high those hills are, but also how far away they are. Imagine standing in a valley; the higher and closer the surrounding peaks, the more sheltered you feel, right? Those higher angles where the land meets the sky? Those angles actually tell you how protected you are.

And why should you care? Turns out, knowing the topographic exposure of a place is super useful in a bunch of different fields.

• For foresters, it’s key to figuring out which trees are most at risk from wind damage.
• Meteorologists use it to model weather patterns.
• Wind energy companies use it to find the best spots for wind turbines.
• Even folks studying snow care about it, because it affects how snow accumulates.
• Pilots can use it to determine the potential availability of GNSS signal.

Okay, so how do you actually calculate this thing? Well, while there isn’t a single “topographic exposure” button in ArcGIS, you can definitely figure it out using the Raster Calculator. Think of it as your digital terrain analysis playground.

Here’s the general idea, borrowing a bit from how it’s done in other software like GRASS GIS:

A few tips for success:

• Pay attention to syntax. The Raster Calculator is a bit picky about how you write your formulas.
• Get friendly with the functions. Atan, Max, and the basic math operators are your friends here.
• Think about cell size. If each cell in your DEM is 25 meters wide, then a spot four cells away is 100 meters distant.
• Handle those “NoData” values carefully. You don’t want them messing up your calculations.
• Be patient! Raster calculations can take a while, especially with big datasets.

Now, the Raster Calculator isn’t the only way to tackle this problem. Here are a few other tricks you can use in ArcGIS:

• Viewshed analysis: This shows you what areas are visible from a specific point. It’s not exactly topographic exposure, but it gives you a sense of how exposed a spot is.
• Terrain analysis tools: ArcGIS has tools for calculating slope, aspect (the direction a slope faces), and hillshade. You can use these as ingredients in your topographic exposure recipe.
• Spatial Analyst and 3D Analyst extensions: These add-ons give you even more tools for playing with terrain data.

In conclusion, figuring out topographic exposure with the ArcGIS Raster Calculator is a bit like detective work. You’re using the tools at your disposal to uncover hidden information about the landscape. By understanding how sheltered a location is, you can gain valuable insights for all sorts of applications. So go ahead, fire up ArcGIS, and start exploring!