RUSLE calculation: LS factor data loss

Question

I am using Arc Hyrdo for the first time in order to create a map using the Revised Universal Soil Loss Equation. I am using hydro to create a flow accumulation raster which I will later use in the raster calculator with a slope layer to determine an LS factor for the area I'm working on. I am following the following sources in doing so:

http://bss.sfsu.edu/jdavis/geog621/projects%20and%20data/Smulyan_Final%20Paper.pdf
http://www.utexas.edu/depts/grg/hudson/grg360g/EGIS/labs_04/Lab9/lab9_soil_erosion_05.htm
http://www.utexas.edu/depts/grg/hudson/grg360g/EGIS/labs_04/Lab6/lab6_spring05.htm

My accumulation raster appears to be correct according to the pictures they have in one of the sources. I believe my slope calc is also right but im not as sure. When i follow the calculation shown in both the sfsu and utexas sources (1.6 * Pow(([flowacc] * resolution) / 22.1, 0.6) * Pow(Sin([tempoal_slope] * 0.01745) / 0.09, 1.3)) my LS calc becomes very pixelated and there are many pixels with "no data," despite the fact that there is no missing data in the slope or accum rasters.

Has anybody encountered this problem before or have any advice from a similar problem with the raster calculator in the past? Any help would be awesome!

Kyle

LS Calc.JPG

Accum.JPG

Slope.JPG

Munuvelu_vese · Answer

hello, can you please tell me in SAGA Gis, which options should I select under Type of slope, specific catchment area. It would be of great help. Thank you.

HowardSchulz · Answer

Hi, the "no-data" pixels are, presumably, because you have your slope raster in degrees, convert it to radians. There is actually a ready script awailable: LSscript for ArcGIS by van Remortel v30-09-11.zip just Google it. You might also find it useful to check the following articles out:

Boehner, J., Selige, T. (2006):
Spatial Prediction of Soil Attributes Using Terrain Analysis and Climate Regionalisation'
In: Boehner, J., McCloy, K.R., Strobl, J.: 'SAGA �?? Analysis and Modelling Applications', Goettinger Geographische Abhandlungen, Vol.115, p.13-27

Desmet & Govers (1996):
'A GIS Procedure for Automatically Calculating the USLE LS Factor on Topographically Complex Landscape Units'
Journal of Soil and Water Conservation, 51(5):427.433

Kinnell, P.I.A. (2005):
'Alternative Approaches for Determining the USLE-M Slope Length Factor for Grid Cells.'

Moore, I.D., Grayson, R.B., Ladson, A.R. (1991):
'Digital terrain modelling: a review of hydrogical, geomorphological, and biological applications'
Hydrological Processes, Vol.5, No.1

And I don't want to scare you:)))), but there is a whole bunch of different algorithms of LS-factor calculation out there, they produce the same data distribution, but absolute values are up to 4-5 times different %), check out which works best for your terrain. And the last but the most important, no offence to ESRI and ArcGIS, but check SAGA GIS out, it's free and open, runs both in Windows and Linux and has already many of such functions (LS-factor calculation as well) built in, that can be with just a couple of clicks right from DEM calculated.

Good Luck!