I am using SAGA - Universal Kriging (Global) for this, but I am stucked. I have grid (.tif) for Serbia with elevation values, and .shp file with points that have mean yearly temperature. I want to create a map using these two files and to take in to the account that Temperature gradient in Serbia is 0.6°C. Temperature gradient means that for every 100m temperature is changed for 0.6°C Also i have the elevation for the .shp file with points, but i don't know how to combine all this. So I want to display a map of the temperature, extrapolated around the known points according to the DEM. Is that possible?
Let me try to summarize the workflow you have taken to obtain a trend surface to be an input grid to the UK algorithm.
Background of this topic would have been like this: (A) There is DEM and measured temperature data available. It is given the temperature generally follow the
-0.6 deg-C per 100m trend. (B) In perfect world the temperature curve should be like the gray curve, but the recorded temperature show certain deviation.
So a workflow (detailed below) taken was, create a surface first by Multiple Regression Analysis considering both measured temperature and elevation, and then removing residual errors.
- Create a "pseudo- temperature grid" by multiplying temperature gradient with DEM. [Grid calculator] Recommended equation was
20 - 0.006 * g1where 20 was notional (intercept) temperature. (It would have been trial and error to find best intercept value).
- Create a Regression grid from measured temperature data and pseudo-temperature grid. [Multiple Regression Analysis Tool]
- Create a residual grid by (a) Calculate difference between measured temperature and the regression grid. [Subtract] and store the difference into the attribute table of the measured point shapefile. (b) Interpolate the difference. Recommended tool was [Multilevel B-Spline] but any gridding tool does this job. (c) Subtract this residual grid from the regression grid. [Grid calculator]
Final output is a temperature trend surface (red dots; above picture), conditioned at the measured locations.
Markoneo, please edit as you think necessary. I likely have missed some steps you have taken.