**5. Conclusions**

In this paper, we demonstrated the ability to create an index from hyperspectral data to accurately identify cacti. We used a hand-held spectroradiometer and two imaging spectrometers to collect spectral information from cholla, barrel, and prickly pear cacti plants and other prevalent landscape features. Based on those collections, we identified three unique aspects in the spectral reflectance signatures for cacti at 862 nm, 972 nm, and 1072 nm bands of the electromagnetic spectrum. Using those three portions of the cacti spectral signatures, we calculated two normalized difference indices: Cacti 1 (862 nm and 972 nm) and Cacti 2 (972 nm and 1072 nm). We then used hyperspectral data captured by drone and airplane to show the applicability of the Cacti indices at various spatial resolutions. Cacti samples showed spectral uniqueness in both the 3 cm drone hyperspectral imagery and the 1 m aerial hyperspectral imagery using the cacti indices.

Whether for conservation or control applications, the cacti indices derived from aerial platforms can help identify cacti across larger landscapes than is possible with field-based measurements. Hyperspectral data provide more precise spectral observations of plant characteristics than multi-spectral imagery sources. Though hyperspectral imagery availability is currently limited, interest in the technology is strong across land management, agriculture, and mining industries. Availability of hyperspectral imagery at multiple airborne and spaceborne scales is likely to proliferate in the near future.

**Author Contributions:** Conceptualization, W.J.D.v.L. and C.C.; methodology, W.J.D.v.L., C.C. and K.H.; software, K.H., C.C. and J.K.G.; validation, W.J.D.v.L., C.L.N., C.C., K.H. and J.K.G.; formal analysis, W.J.D.v.L., C.L.N., C.C., K.H. and J.K.G.; investigation, W.J.D.v.L., C.L.N., C.C., K.H. and J.K.G.; resources, W.J.D.v.L.; data curation, C.L.N., K.H. and J.K.G.; writing—original draft preparation, K.H.; writing—review and editing, W.J.D.v.L., K.H. and J.K.G.; visualization, K.H. and J.K.G.; supervision, W.J.D.v.L.; project administration, W.J.D.v.L.; funding acquisition, W.J.D.v.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding. Technology and Research Initiative Fund (TRIF) funding was provided to purchase the hyperspectral drone.

**Data Availability Statement:** Data can be obtained by contacting the lead author.

**Acknowledgments:** The authors appreciate the research support provided by the Arizona Remote Sensing Center. We are thankful to Angela Chambers, who helped with data acquisition and image interpretation. We downloaded the NEON AVIRIS hyperspectral data from the NSF NEON Data Portal.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
