SMITH, B. J.; YAN, J.; COWLES, M. K. Unified Geostatistical Modeling for Data Fusion and Spatial Heteroskedasticity with R Package ramps. Journal of Statistical Software, [S. l.], v. 25, n. 10, p. 1–21, 2008. DOI: 10.18637/jss.v025.i10. Disponível em: https://www.jstatsoft.org/index.php/jss/article/view/v025i10. Acesso em: 5 oct. 2022.