COMPARISON OF IMAGE-DERIVED SOIL LICHEN MAPS WITH FIELD DATA AND MAPPED GEOLOGIC UNIT

We are testing the use of three-band Color Infrared (CIR) imagery to map soil lichen cover. The image-derived soil lichen maps will be used in the analysis of soil lichen relationships with geomorphic features and geologic units. The field area for this study is the Hayden piedmont in the eastern Mojave Desert, California. The CIR imagery has high spatial resolution (7 cm pixels) and was collected by low-altitude helicopter flights. The imagery has been georeferenced so that we can compare it in a GIS with data collected in the field and other spatially referenced data, such as geologic mapping. In order to focus on the soil lichen, we first masked out the plants, producing an image of just the inter-plant space. The plant mask was created using band ratios of the original three-band CIR imagery; this plant mask removes both photosynthetic and non-photosynthetic vegetation. We then explored contrast enhancements and additional band ratios to create an index sensitive to the amount of soil lichen cover in the inter-plant space. After determining cutoff values for this index associated with the presence or absence of soil lichen, we can create a map of soil lichen cover. In order to assess the accuracy of this map, we are comparing the image-derived map to maps created from field work. Field data will be recorded on georeferenced balloon imagery (pixel size of 4 cm.) Using the balloon imagery as base data allows us to create georeferenced field maps of the soil lichen cover instead of traditional point transects. Both the image-derived map and the georeferenced field map can be compared in a GIS. The field maps are the ground truth against which we are comparing derived soil lichen maps from the imagery. To assess the relationship between soil lichen cover and geologic unit, we are comparing the image-derived soil lichen map with detailed (1:10000) geologic mapping. In addition, the soil lichen maps will be compared with plant and channel locations to assess the spatial relationship between soil lichen cover and geomorphic features.