Welcome to the list. The R package Distance will allow you to examine
the effect of features like NDVI upon "detectability", rather than the effect upon density itself. Alternatives for you to examine the effect of environmental covariates upon density itself can be examined via use of the `dsm` package,see Miller et al. (2013)
Another alternative for examining the effect of environmental covariates upon density can be found in these papers.
Buckland, Stephen & Russell, Robin & Dickson, Brett & Saab, Victoria & Gorman, Donal & Block, William. (2009). Analyzing Designed Experiments in Distance Sampling. Journal of Agricultural Biological and Environmental Statistics. 14. 432-442. 10.1198/jabes.2009.08030.
Evans, Kristine & Burger, L. & Oedekoven, Cornelia & Smith, Mark & Riffell, Sam & Martin, James & Buckland, Stephen. (2013). Multi-region response to conservation buffers targeted for Northern bobwhite. Journal of Wildlife Management. 77. 716-725. 10.1002/jwmg.502.
Analyses for these two approaches do not live as yet in R packages. Let us know if you have further questions.