Discussion

Wooden walkways provide good access to some portions of the study bogs, but wading through soft peat and knee-deep water is necessary to reach many areas. In this regard, the high portability of equipment is critical for successful KAP in the bog environment. The combination of late summer

FIGURE 14-10 Oblique overview of Nigula bog looking toward the west. Narrow wooden footpath (~40 cm wide) is visible in lower left portion, and a mineral island appears in the right background. Kite aerial photo by SWA and JSA, September 2001.

FIGURE 14-11 Vertical view in eastern portion of Nigula bog. Sphagnum cuspidatum forms a silvery green "mat" floating in parts of some pools. The reddish-brown zones include Sphagnum magellanicum and S. rubellum. Heather covers much of the mottled green surface along with a few small pines (note shadows). A portion of the footpath is visible in lower left corner. Taken from Aber et al. (2002, fig. 3).

FIGURE 14-11 Vertical view in eastern portion of Nigula bog. Sphagnum cuspidatum forms a silvery green "mat" floating in parts of some pools. The reddish-brown zones include Sphagnum magellanicum and S. rubellum. Heather covers much of the mottled green surface along with a few small pines (note shadows). A portion of the footpath is visible in lower left corner. Taken from Aber et al. (2002, fig. 3).

weather and early autumn vegetation color makes for excellent results in September. However, widespread burning of agricultural waste renders October photographs hazy (see Fig. 4-28), and low sun angle (at 58°N latitude) creates excessive shadowing after fall equinox.

High-resolution SFAP may be applied for microstructural investigations and analysis of mires at scales of 1:100-1:1000 (Masing, 1998). The civilian imagery interpretability rating scale has 10 rating levels (0-9; see Table 10-1 and Chapter 10.2). The resolution of vertical digital kite aerial photographs (2-5 cm) provides for interpretability ratings of 7-8 (Leach-tenauer et al., 1997). This ground resolution is an order of

FIGURE 14-12 Low-oblique view over Salupeaksi, a tree-covered mineral island (a drumlin), in the middle of Nigula bog. Notice the marked forest zones of the island. A, pine; B, birch (partly bare); C, ash, elm, maple, and other deciduous hardwoods, some of which are displaying fall colors. Kite line crosses the lower right corner of photograph. Taken from Aber et al. (2002, fig. 4).

FIGURE 14-12 Low-oblique view over Salupeaksi, a tree-covered mineral island (a drumlin), in the middle of Nigula bog. Notice the marked forest zones of the island. A, pine; B, birch (partly bare); C, ash, elm, maple, and other deciduous hardwoods, some of which are displaying fall colors. Kite line crosses the lower right corner of photograph. Taken from Aber et al. (2002, fig. 4).

magnitude more detailed than conventional airphotos. The Estonian examples demonstrate remarkably intricate and complex spatial patterns and depict abundant open water (pools) developed within bogs at the microstructural level (see Fig. 5-21). On this basis, the areas shown by vertical SFAP (~1 ha) could be used as training sites for improved interpretation and classification of land cover depicted in conventional airphotos and satellite images.

A direct comparison of color-visible and color-infrared images favors the visible portion of the spectrum for revealing overall variations and details for all types of land cover in bogs. The natural colors and relative ease of interpretation are advantages for color-visible imagery in both vertical and oblique views. Photosynthetically active green plants strongly absorb red (0.6-0.7 mm) light and strongly reflect near-infrared (NIR, 0.7-1.0 mm) energy (Colwell, 1974; Tucker, 1979), which is shown vividly in color-infrared photographs. Moss (Sphagnum sp.), however, has a considerably lower NIR reflectivity, in general, compared to trees and grass. The seasonal peak of NIR reflectivity for moss occurs in late summer, whereas most deciduous trees and grass have their peaks in late spring and early summer (Peterson and Aunap, 1998). Thus, interpretation of bog vegetation takes some care in terms of spectral characteristics and seasonal conditions.

Mires are normally rather dark features in most conventional airphotos and satellite images. The reason for this is apparent from examination of the color-infrared image (Fig. 14-8). The zone of active photosynthesis is distributed in narrow strips or clumps, no more than 1-2 m wide, at the margins of pools and hollows. Recognition of these patterns and photosynthetic activity requires submeter spatial resolution. In lower-resolution imagery, however, strong near-infrared reflections from such narrow moss zones are blended with weak reflections from adjacent water, mud, and hummocks to create an average low value for each pixel in the image. These results suggest that while plant activity is low overall in late summer, bogs contain narrow zones within and around pools that support a high level of photosynthesis. This finding may have significant implications for accumulation of peat biomass, growth of bog microtopography, methane flux, and related environmental factors.

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