Remote Detection of Red-Edge Spectral Characteristics in Floating Aquatic Vegetation

Abstract

The vegetation red-edge of terrestrial plants is a key biosignature for detecting Earth-like habitable exoplanets. Although water is essential for plants, an excess of water can limit the distribution of terrestrial vegetation. On planets with extensive water coverage and limited land, floating vegetation on the water's surface could serve as a crucial indicator of life. This study examined the spectral reflectance of floating plants across various scales, from individual leaves to lake-wide vegetation coverage. Our comparisons between individual leaves revealed that the red-edge of floating plants was equivalent to or even more pronounced than that of terrestrial plants. Although water can reduce plant reflectance, the naturally low reflectance of water enhances the detection sensitivity for floating vegetation. Seasonal changes, such as the proliferation of floating plants in summer and their decline in winter, lead to significant variations in lake reflectance. By analyzing satellite images of lakes and marshes over a five-year period, we confirmed that these seasonal variations in reflectance reliably indicate the presence of floating vegetation. The seasonal signal showed robustness to the effects of clouds, which pose another challenge on water-rich planets. We propose that floating vegetation be considered alongside, or even in place of, terrestrial vegetation in the search for extraterrestrial life.