Using Reflectance for Species Identification
Paired STS spectrometers (upwelling and downwelling orientation) were used to identify aquatic and shoreline plants for use in controlling invasive species like the Brazilian water weed Egeria densa.
The spectra of Egeria densa samples are shown below, along with other plants from a pond in Wesley Chapel, FL. The dip at 670nm is from chlorophyll. Accessory pigments and carotenoids influence the spectra below 670nm. High reflectance in the NIR is typical for most plants.The ratio of reluctance in the NIR compared to 670nm region is called NDVI.
Differences in NDVI (normalized difference vegetation index) are often used with remote sensing that use a few discrete wavelength bands. The use of full spectra though permits comparison of spectral shapes. Statistical analysis shows the similarity of shape among the Egeria spectra and the differences compared to the other plant species.
The significance is that calculation of the index is rapid and could be used for real time detection, guiding pilots to closer looks at suspicious patches of Egeria.
The STS spectrometers are very light – just 68g – and they can be run using a small SBC such as the raspberry Pi. STS spectrometers are low cost (just $1500) and are available online in UV, VIS and NIR versions. VIS STS units are also available for rent.