Global Mapper, excel spreadsheets, and HSQI
Updated: Feb 8, 2019
Today we continued working on our detailed excel spreadsheets by using global mapper to identify slope angles of the areas that we marked. Last week we were using surfer to do this but because the program works with very large files getting through all of Ruta 27 would’ve taken a ridiculous amount of time. The computers at Lanamme can handle very large files because they have servers but because we’re working on laptops we had to think of another solution. We switched over to global mapper by converting all the slope files we had made on surfer to something that global mapper can read instead. We translated the slope key as well and then we were able to continue adding to the excel spreadsheets this way. In addition to recording slope angles we also have to use the LiDAR images to explain why we marked that particular area and what kind of landslide or characteristics that area has. In the beginning we were flying through the work but now we have to slow down and carefully look at the topography in order to record useful and accurate data.
Towards the end of the day Paulo met up with both of us to discuss what we’re going to be doing this upcoming week and what the fall and spring semester will look like. Paulo also took the time to explain the theory behind what the surfer software does automatically and how finding slope calculations would’ve looked like 20 years ago without the surfer software. Geographers would have had to make several different cuts along the route, get a profile view of the terrain, and use Pythagorean theorem find the angles of the slopes. Surfer does this instantly and pixel by pixel which makes it able to deliver highly detailed and accurate slope maps. It’s fascinating to see how rapidly technology has been able to evolve and advance, possibly in the span of a person’s career, and how it has been able to improve the efficiency of tasks in the workplace.
After we finalize our spreadsheets it will be possible to then start creating density maps that show which kilometer blocks along the route have the most landslides, characteristics of a landslide already underway, or indicate the potential for a landslide to occur. The density map will be able to help us direct our attention to places along the route that need priority. Another way that we will create density maps is by applying the Hill Slope Quality Index (HSQI) method. This method is very helpful and has been utilized by a handful of people. We personally know of 2 people who are currently using the HSQI method to create density maps for their thesis. The reason we are making density maps 2 different ways is to prove that the HSQI is a better method by comparing it to the old way of creating them. For the HSQI method we will be using different formulas depending on the topographical analysis and we’ll need geotechnical information about particular regions along the route because different materials have different stabilization angles. Hydrological information, friction angles, slope angles, and other information will all be used in conjunction to create a HSQI along the whole route.
The HSQI data becomes useful in terms of making corrections to problem areas. Factor of safety graphs are then used to develop correction factors, Fc. Fc helps you obtain a value called HC which stands for height correction for a slope.
Picture 1: My landslide notes that I reference when working on excel.
Picture 2: Manually finding slope angles using Pythagorean theorem and terrain profile pictures
Picture 3: Different situations need different formulas. Ex) slope angles, type of slide, whether there's water present, etc.
Picture 4: Formulas
Picture 5: The different values that are needed to make a HSQI
Picture 6: An example of a completed HSQI spreadsheet.
Picture 7: Formula for height correction. ActualHeight/CorrectionFactor = HeightCorrection
Picture 8: Cuts made along a route with their respective terrain profiles.
Picture 9: Using HSQI to make a density map. Red meaning: an area with a lot landslides and/or high risk. Green meaning low risk.