SNRI: A Signed Normalized Range Index for Remote Sensing of Panax notoginseng Plantations

Panax notoginseng is a widely recognized medicinal herb in Chinese traditional medicine. Investigating the cultivation of P. notoginseng is crucial for ecological preservation and effective land management. In our study, we conducted an analysis of the spectral properties of P. notoginseng plantations along with various other land cover types. As a result, we have introduced a novel index called the signed normalized range index (SNRI), based on the maximum and minimum reflectance values across all bands of the multispectral imagery. Through experiments conducted on Landsat-8 operational land imager (OLI) images obtained from Yunnan, China, we performed quantitative assessments of separability measurements. SNRI has shown great potential in enhancing the identification of P. notoginseng, with an average Jeffries–Matusita (J–M) separability of 1.378 compared with other land covers. Furthermore, we conducted a comparative analysis of the support vector machine (SVM) classification results using several spectral indices for dark target extraction. The comparison affirmed the superior performance of SNRI in accurately distinguishing P. notoginseng plantations from other land cover types. It is promising to explore the application of SNRI in remote sensing estimation and change monitoring of the P. notoginseng planting area, as well as other land covers with similar lower reflectance ranges.