The gradient calculation calculates the devrivative of the data in the azimuth specified.
Options
Azimuth - This is the direction of the derivative, in the plane of the data.
Order - This is the order of the derivative.
References
Cooper,G.R.J., Cowan, D.R. 2007. Enhancing linear features in image data using horizontal orthogonal gradient ratios. Computers and Geosciences, 33, p.981-984