Spectral Characteristics of Greenland Lichens

Abstract

Spectral reflectance measurements conducted during two field campaigns in west Greenland, and in the laboratory using samples collected during those campaigns, are discussed to evaluate the spectral signature of lichens. Given the diversity in lichen species, colors, and appearance — ranging from crust-like (crustose) to almost like mini shrubs (fructicose) — it is not surprising that no single signature was found. Some of the brighter fructicose lichens have reflectance characteristics very similar to those of green vegetation, with a pronounced rise in reflectivity around 750 nm. However, the most abundant lichen species covering rocks in the ice-marginal zone of west Greenland are dark grey to black crustose and foliose ephilithic (rock-growing) lichens and the shape of the reflectance spectrum for these lichens is generally very different from that of other surface types and landcovers, with near-zero reflectance at visible wavelengths, and a maximum around 1 600 nm. This characteristic allows rock-covered lichen to be identified on multispectral satellite imagery.L’évaluation de la signature spectrale des lichens est effectuée à partir de mesures prises en laboratoire et sur le terrain, au Groenland occidental. Aucune signature spécifique ne peut être identifiée, en raison de la diversité des espèces quant à leur couleur et à leur port, allant de la croûte à l’arbuste nain. Les lichens arbustifs les plus brillants montrent une signature spectrale semblable à celle des plantes vertes, avec un pic très prononcé autour de 750 nm. Toutefois, les lichens les plus abondants sur les roches à proximité des glaces sont gris foncés à noirs et du type crustacé ou foliacé; leur spectre de réflectance montre une allure très différente de celle des autres types de surface et de couverture, et se rapproche de zéro dans le spectre visible avec un pic autour de 1 600 nm. Cette caractéristique permet l’identification des roches recouvertes de lichens par l’imagerie satellitaire multispectrale

Inhibition of Primary Photosynthesis in Desiccating Antarctic Lichens Differing in Their Photobionts, Thallus Morphology, and Spectral Properties

“…However, for both, a biphasic increase in the red-edge region was found as follows: there was a higher rate within the ranges of 680 nm to 710 nm and 710 nm to 800 nm, respectively. The presence of a red-edge increase in spectral reflectance is a characteristic of chlorolichens that has been reported and documented for many species that exhibit a large variety of thallus colors (see [ 71 , 72 ]). In general, hydrated chlorolichen samples, except for the black H. lugubris , showed lower reflectance values than in the dry state.…”

Spatial and Temporal Variability in the Onset of the Growing Season on Svalbard, Arctic Norway — Measured by MODIS-NDVI Satellite Data

“…The State QA flags often fail in detecting thin clouds, covering sparsely vegetated areas. In sparsely vegetated areas, where rocks or saxicolous lichens dominate, the reflectance might have the same signature as clouds in the short wave infrared parts [42], which could be the explanation. Some of these clouds could be seen by visual evaluation or by comparing with median values from the previous years of the same 8-day period.…”

Intermittent thinning of Jakobshavn Isbræ, West Greenland, since the Little Ice Age

“…1). This, Camp-2, was occupied for several days during July 2003, to establish a retreat sequence, to map fresh lateral moraines and to provide field-based validation for trimline mapping from multispectral satellite images (Csatho and others, 2005; Van der Veen and Csatho, 2005).…”