V factor should be accumulated by median

Question

V factor should be accumulated by median

shahab271069 opened this issue 3 years ago · comments

shahab271069 commented 3 years ago

Hey

I checked your code and the V factor in Rusle.Sfactor calculation should be accumulated by median.

Please check it. It should be median because the Sfactor are extremely underestimated.

Best
Shahab

William Ouellette · Answer 1 · Thu Oct 21 2021 04:32:23 GMT+0800 (China Standard Time)

Hi Shahab,

The V factor is a model of a natural phenomenon, which is the impact of annual vegetation cover on soil erosion. The more often and more dense vegetation is, the higher the L*V factor should be.

In order to truly embody the temporal dynamics of vegetation cover on soil erosion, calculating the integral of the FCover curve would probably be the most accurate way to model it, and taking the mean of that sequence may be an over-simplification (so would taking the median in that sense).

What we could do is use a trapezoidal approximation to calculate the area under the curve and better model the temporal character of the V factor, similar to what is done here for the AUC:
https://gis.stackexchange.com/questions/265623/how-to-access-accuracy-of-binary-probability-in-google-earth-engine
If you agree, I can create a pull request to update it.

Regards,

William

shahab271069 · Answer 2 · Thu Oct 21 2021 17:53:49 GMT+0800 (China Standard Time)

Hi William

Thank you for your answer. Yes, you are right, It should be calculated by integral form. I agree, because this may provide more realistic V factor. Please create a pull request to elevate this part.

Thanks
Shahab

William Ouellette · Answer 3 · Sat Oct 23 2021 05:17:35 GMT+0800 (China Standard Time)

The pull request for review:
#3

shahab271069 · Answer 4 · Sat Oct 23 2021 05:59:33 GMT+0800 (China Standard Time)

Hi William

Thank you for your pull. I checked the values, which I think are comparable with median. However, I will check the results deeply and inform you ASAP.

Regards
Shahab

shahab271069 · Answer 5 · Sat Oct 23 2021 06:41:58 GMT+0800 (China Standard Time)

Hi William

I checked the new version. It has improved the V factor calculation. Therefore, I want to thank you for your magnificent work. I checked it with other available datasets. If you prefer, later I can provide some validation sets of this work.

Best
Shahab

William Ouellette · Answer 6 · Sat Oct 23 2021 16:07:01 GMT+0800 (China Standard Time)

With pleasure! In the meantime, I will proceed with the merge.