Hello everyone,
I’m currently working with the SDR and NDR models using a 30m × 30m SRTM DEM. I have a question about interpreting and converting the output units.
According to the InVEST User Guide, the model outputs are in metric tons/hectare/year. My outputs maintain the same 30m × 30m resolution as my input DEM
Since each pixel represents 900 m² (30m × 30m = 0.09 hectares), and the outputs are already given in tons/hectare/year, do I need to convert these values to get the total sediment/nutrient load per pixel? How can i do such conversion?
I want to ensure I’m correctly interpreting the outputs before proceeding with my analysis.
Thank you in advance for your help!
Hi @tharindu_bawantha,
Since the raster results are given in metric tons/hectare/year, to convert the per hectare values to per pixel values, you need to adjust by the size of your pixels relative to one hectare. For example: If 1 pixel = 900 m2 (as yours do, with a 30m x 30m resolution), then the conversion from metric tons per hectare (t/ha) to metric tons per pixel (t/pixel) would be: (t/ha x 1/10000 ha/m2 x 900 m2/pixel) or (the per hectare value x (900/10000)). The number will get smaller when the pixel size is smaller than a hectare.
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Thank you for your valuble solution.
So, After this conversion, the final units of the soil erosion came as t/pixel/year or t/ha/year?
I need the data as in the t/ha/yr units.
As long as you’re using a version of InVEST >= 3.15.0, the SDR and NDR raster outputs are already given in t/ha/year. The conversion is only necessary if you want to instead get values in t/pixel/year.