The Earth as an extrasolar planet:thevegetation spectral signature today and during the last Quaternary climatic extrema

摘要

The so-called vegetation red-edge (VRE), a sharp increase in the reflectance around 700 nm, isa characteristic of vegetation spectra, and can therefore be used as a biomarker if it can be detected in anunresolved extrasolar Earth-like planet integrated reflectance spectrum. Here, we investigate the potentialfor the detection of vegetation spectra during the last Quaternary climatic extrema, the Last GlacialMaximum (LGM) and the Holocene optimum, for which past climatic simulations have been made.By testing the VRE detectability during these extrema, when Earth's climate and biomes maps weredifferent from today, we are able to test the vegetation detectability on a terrestrial planet different from ourmodern Earth. Data from the Biome3.5 model have been associated to visible Global Ozone MonitoringExperiment (GOME) spectra for each biome and cloud cover to derive Earth's integrated spectra forgiven Earth phases and observer positions. The VRE is then measured. Results show that the vegetationremains detectable during the last climatic extrema. Compared to the current Earth, the Holoceneoptimum, with a greener Sahara, slightly increases the mean VRE on one hand, while on the other hand,the large ice cap over the northern hemisphere during the LGM decreases vegetation detectability.We finally discuss the detectability of the VRE in the context of recently proposed space missions.