Remote Sensing for Identification and Classification of Wetland Vegetation

Abstract

Multispectral photography and ground truth were obtained on an area 12 miles (19.3 km) east of Bemidji, Minnesota, to identify and map wetlands less than 2 acres (0.8 hectare) in size, to map emergent vegetation in lakes, and to explore the feasibility of classifying vegetation from aerial photographs. Wetlands less than 2 acres in size were identified on photography taken in May 1971, and emergent vegetation was recorded on purposely overexposed infrared black and white photography from a flight in September 1971. Several vegetation types and species groups were recognizable with the aid of color, color infrared, and black and white infrared photography. Proper timing of flights, use of multispectral photography, and knowledge of the ecology of the area are considered essential for wetland mapping by remote sensing. J. WILDL. MANAGE. 38(2):308-314 Investigations of the ecology of birds and other wildlife usually require data on the area of and types of habitat available to the animals. Measurements of habitat made from ground surveys are often time-consuming and, therefore, must be restricted to relatively small areas. Remote sensing is a relatively new tool, which, when used in conjunction with ground surveys, enables the ecologist to rapidly survey large areas of land and water, and discover details that are not readily apparent from ground surveys (Colwell 1967). For years, foresters have made extensive use of remote sensing for timber management and inventory (Avery 1968), but work on aquatic habitats has been more restricted. Studies by Kelly and Conrod (1969), Lukens (1968), Cameron (1950), Zohari et al. (1955), Mathisen (1966), Olson (1964), Nelson et al. (1970), and Work and Gilmer (1973) have demonstrated that remote sensing has great promise for wetland mapping and inventory. Recently many investigators have had considerable success in recognizing wetland plant communities and even plant species with the aid of color and color infrared films (Anderson 1968, Anderson 1969, Thompson 1972, Russell and Wobber 1972, Reimold et al. 1973, Seher and Tueller 1973). We required detailed habitat maps for a long-term investigation of waterfowl ecology in Minnesota (Gilmer et al. 1973). Preliminary maps were prepared from ground surveys and from 1:15,840 infrared summer photography obtained from the U.S. Forest Service, but difficulty was experienced in distinguishing small wetlands under the canopy of a hardwood forest. Vegetation in lakes was difficult to map either from a boat or with the aid of aerial photographs. This report considers the use of multispectral photography: (1) to find and map wetlands less than 2 acres in size (minimum size mapped by Mathisen [1966]) under a forest canopy, (2) to accurately map stands of emergent vegetation in lakes, and (3) to explore the feasibility of using multispectral photography to classify wetlands.