Curvature, the second derivative of elevation, is a very useful terrain derivative. It describes how convex or concave a surface is, which helps predict soil moisture (among other things). The basic terrain analysis feature in SAGA calculates plan curvature and profile curvature. Profile curvature goes with the direction of maximum slope, which helps estimate acceleration of water across a surface. Picture a contour line, which goes against the direction of slope. This is where plan curvature is measured.
Some other important types of curvature are general curvature, or the difference between plan and profile curvatures, and tangential curvature, which is exactly perpendicular to profile curvature. SAGA can calculate many more curvature types, but those are the four I use most often.
Like I mentioned previously, plan and profile curvature are part of the basic terrain analysis procedure in SAGA. The Slope, Aspect, and Curvature procedure can calculate plan, profile, general, tangential, and other types of curvature. To get started, open your elevation file. If you need a reminder for how to import a DEM in SAGA, check out the intro to SAGA post here.
Once you have your elevation model opened, go to “Geoprocessing” on the main menu tab, then “Terrain Analysis” and “Mophometry.” When you select “Slope, Aspect, and Curvature,” the following pop up will appear. Select your grid system and elevation file, and then select “create” for any types of curvature you want SAGA to calculate. From there, select “Okay” and all the files you requested will be calculated.
SAGA makes calculating curvature very efficient. I use curvature in my research because identifying concave parts of the landscape helps me predict where water will be more available for plants. How do you use curvature?
Spatially Challenged 