Interesting paper. However, in regard to geostatistical approach, it should be worth to mention and eventually test the family of roughness indices based on an robust version of variogram presented in the paper Trevisani and Rocca (2015). There, you will find also a more extended reference to applications of geostatistics for geomorphometry and remote sensing.

1. Trevisani, M. Rocca,

MAD: robust image texture analysis for applications in high resolution geomorphometry,

Computers & Geosciences,

Volume 81,

2015,

Pages 78-92,

ISSN 0098-3004,

https://doi.org/10.1016/j.cageo.2015.04.003.