Remote Sensing of Explosives-Induced Stress in Plants: Hyperspectral Imaging Analysis for Remote Detection of Unexploded Threats

Abstract

Explosives contaminate millions of hectares from various sources (partial detonations, improper storage, and release from production and transport) that can be life-threatening, e.g., landmines and unexploded ordnance. Exposure to and uptake of explosives can also negatively impact plant health, and these factors can be can be remotely sensed. Stress induction was remotely sensed via a whole-plant hyperspectral imaging system as two genotypes of Zea mays, a drought-susceptible hybrid and a drought-tolerant hybrid, and a forage Sorghum bicolor were grown in a greenhouse with one control group, one group maintained at 60% soil field capacity, and a third exposed to 250 mg kg −1 Royal Demolition Explosive (RDX). Green-Red Vegetation Index (GRVI), Photochemical Reflectance Index (PRI), Modified Red Edge Simple Ratio (MRESR), and Vogelmann Red Edge Index 1 (VREI1) were reduced due to presence of explosives. Principal component analyses of reflectance indices separated plants exposed to RDX from control and drought plants. Reflectance of Z. mays hybrids was increased from RDX in green and red wavelengths, while reduced in near-infrared wavelengths. Drought Z. mays reflectance was lower in green, red, and NIR regions. S. bicolor grown with RDX reflected more in green, red, and NIR wavelengths. The spectra and their derivatives will be beneficial for developing explosive-specific indices to accurately identify plants in contaminated soil. This study is the first to demonstrate potential to delineate subsurface explosives over large areas using remote sensing of vegetation with aerial-based hyperspectral systems.in soil and is highly mobile unlike TNT and has entered groundwater sources of some communities around military bases [5]. With almost 2000 sites at closed military bases contaminated with UXO, explosives contamination at military testing sites also complicate base conversions after closure [6,7]. Over the course of years of being in soil, ordnance casings containing RDX degrade from contact with water in the form of rain and soil moisture [8]. The sheer volume and diversity of fugitive compounds in the subsurface drives the need for a novel technique that accurately locates contaminants and will allow for safe and rapid remediation.Plants can be used as sentinels to discover what lies in soil beneath the surface. Roots spread out in the subsurface and acquire water, nutrients, and many chemicals present in subsurface soil and groundwater, thereby acting as an in-situ sampling tool. Chemical testing of plant tissues has shown that plants can act as chemical samplers [9] and that uptake is predicted by physio-chemical properties [10]. Compounds that can cross root membranes may cause stress by altering physiological and morphological characteristics, e.g., chlorophyll reductions, decreased stomatal conductance, increased fluorescence, and reduced biomass. Explosives enter plants by crossing root membranes via bulk water transport and are either stored in roots or translocated to leaves where they accumulate [11][12...

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