Moisture Content Assessment in the Hudson Bay Lowlands Through Remote Sensing Technology
Assessing moisture contents of lichens and mosses using ground-based high spectral resolution spectrometers (400-2500 nm) offers immense opportunities for a comprehensive monitoring of northern peatland moisture status by satellite/airborne imagery. This study investigates the impact of various moisture conditions of the lichens Cladina stellaris and Cladina rangiferina, and the mosses Dicranum elongatum and Tomenthypnum nitens upon the spectral signatures obtained. Reflectance and moisture content measurements (using weighing lysimeters) of the above species were made in a laboratory setting, while maintaining the natural moisture conditions of the samples; once the moisture and spectral measurements were complete, the samples were returned to the field and placed in their natural setting, continuously receiving moisture from precipitation and groundwater and losing water through evaporation and drainage. The spectral indices MSI (Moisture Stress Index), Simple ratio, WBI (Water Band Index), NDII (Normalized Difference Infrared Index), and NDWI (Normalized Difference Water Index), were correlated with the moisture contents of the above species. The NDII was most successful in detecting moisture contents for all species, with R2 between 0.44 and 0.67. This study developed species specific indices to improve the detection of the above lichens and mosses moisture conditions. These species specific indices use normalized ratios between the near-infrared (NIR) and shortwave-infrared (SWIR). The improvement of these indices versus the spectral index NDII is significant (10-70%). The relationship between the plants' moisture content and the water table position was examined as well. It was found that the lichens are not responsive to variations in the water table position, while the mosses, specifically D. elongatum, are quite sensitive to changes in the water table position (with R2 0.78, and 0.38 for D. elongatum, and T. nitens, respectively). Thus, the use of the mosses spectral indices, specifically, the D. elongatum index, may contribute to an indirect evaluation of the water table position. Overall, the results of this study suggest that the unique spectral signatures of C. stellaris, C. rangiferina, D. elongatum, and T. nitens allow these species to be detected by satellite and airborne imagery, while the mosses, can be used as indicators of peatlands moisture status.