In GISus-M system, the calculation of C factor grid is based on NDVI data. We developed a interface that is easy to operate which the user can create NDVI data or to use an existing NDVI image. The cover management factor can be determined in two ways in GISus-M, a method proposed by Van der Knijff et al. (1999) and another by Durigon et al. (2014).

One approach to determine the C-factor from remotely sensed data is by Normalized Difference Vegetation Index (NDVI):

where NIR is surface spectral reflectance in the near-infrared band and RED surface spectral in the infrared band. Van der Knijff et al. (1999) proposed a exponential function, after some experimentation, which was investigated whether the NDVI-images could be 'scaled' to approximate C factor values in some alternative way:

where α and β are parameters that determine the shape of the NDVI-C curve. An α-value of 2 and a β-value of 1 seem to give reasonable results for Europe climate conditions (Van der Knijff et al., 1999).

As C factor tends to be higher than calculated by equation above, under tropical climate conditions for same vegetation cover, a new methods was proposed by Durigon et al., (2014) for region with more intense rainfall.

According to same authors, for areas with higher vegetation cover, NDVIs tend towards +1 and C-factors are close to 0. Moreover, The application of equation in a watershed of Atlantic Forest biome and the methods was more accurate in calculating the C factor than that proposed by Van der Knijff et al. (1999).