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Title: INFLUENCE OF INCIDENCE ANGLE ON DETECTING FLOODED FORESTS USING C-BAND SAR

Author
item Lang, Megan
item TOWNSEND, P - UNIV OF WI-MADISON
item KASISCHKE, E - UNIV OF MD

Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2008
Publication Date: 8/26/2008
Citation: Lang, M.W., Townsend, P.A., Kasischke, E.S. 2008. Influence of incidence angle on detecting flooded forests using C-band SAR. Remote Sensing of Environment. 112:3898-3907.

Interpretive Summary: Wetland hydropattern, or spatial and temporal variations in inundation and saturation, is the single most important factor in the formation and functioning of a wetland. Although the importance of hydropattern is widely understood, knowledge is still lacking due to the large amount of resources needed to accurately collect this information on the ground, the inability to use aerial photography during much of the year, and the lack of high spatial resolution topographic maps. Fortunately, imaging radars are emerging as a viable alternative. The goal of this research was to investigate the influence of data collection angle on the ability of C-HH SAR to detect flooding in three forest types (open tupelo-cypress, tupelo-cypress, and deciduous bottomland hardwood forests) during the winter and summer. The influence of data collection angle varies between forest types, especially under flooded conditions, underlining the need to quantify the impact of collection angle on the ability to detect flooding in different forest types. Although previous research suggests that flooding should be easier to detect in forests using smaller angle, winter SAR data, this research did not support these findings. Instead it demonstrated that larger angles can be used to detect flooded forests during the winter and summer. Based on these results, a wider variety of angles and times of the year should be considered when using C-band SAR to monitor inundation beneath the forest canopy. The ability to use a wider range of angles will increase the potential frequency of studies dependent on accurate information regarding flooding beneath trees.

Technical Abstract: Wetland hydropattern, or spatial and temporal variations in inundation and saturation, is the single most important factor in the formation and functioning of a wetland. Although the importance of hydropattern is widely understood, knowledge is still lacking due to the large amount of resources needed to accurately collect this information on the ground, the inability to use conventional, optical remote sensing methods during much of the year, and the lack of high spatial resolution digital elevation models. Fortunately, imaging radars are emerging as a viable alternative. The goal of this research was to investigate the influence of incidence angle on the ability of C-HH SAR to detect flooding in three forest types (open tupelo-cypress, tupelo-cypress, and deciduous bottomland hardwood forests) during the leaf-off and leaf-on seasons. Angular signatures vary between forest types, especially under flooded conditions, underlining the need to quantify the impact of incidence angle on the ability to detect flooding in different forest types. Although previous research suggests that flooding should be easier to detect in forests using smaller incidence angle, leaf-off SAR data, this research did not support these findings. Data collected at an incidence angle of 23.5o exhibited a 2.14 dB leaf-off and 1.34 dB leaf-on difference between flooded and non-flooded forests, demonstrating a lower ability to detect flooding than data collected at incidence angles between 27.5o and 43.5o. Instead it demonstrated that larger incidence angles can be used to detect flooded forests during the leaf-off and leaf-on seasons. Based on these results, a wider variety of incidence angles and times of the year should be considered when using C-band SAR to monitor inundation beneath the forest canopy. The ability to use a wider range of incidence angles will increase the temporal resolution of studies dependent on accurate information regarding inundation beneath forest canopies.