Revised Calculations Optimal Image Resolution

These initial calculations revealed that the idea of covering the whole area of interest in a single shot had to be abandoned because the GSD was larger than desired for detailed gully monitoring. Therefore, the survey design was recalculated learbeitsn Ansicht Chronik {gleichen E*l/« Hffe learbeitsn Ansicht Chronik {gleichen E*l/« Hffe

FIGURE 9-15 Orthophoto of the Gully Belerda area in the SIGPAC viewer (eMinisterio de Agricultura, Pesca y Alimentation de España, 2008). The screenshot was used in graphic software for compiling a flight-planning map. Minimum area of interest for monitoring indicated in red, corresponding ideal image footprint in green. Exemplary footprint for optimal image resolution (GSD = 2 cm) in yellow. White arrow shows position and viewing direction of Figure 9-14.

FIGURE 9-15 Orthophoto of the Gully Belerda area in the SIGPAC viewer (eMinisterio de Agricultura, Pesca y Alimentation de España, 2008). The screenshot was used in graphic software for compiling a flight-planning map. Minimum area of interest for monitoring indicated in red, corresponding ideal image footprint in green. Exemplary footprint for optimal image resolution (GSD = 2 cm) in yellow. White arrow shows position and viewing direction of Figure 9-14.

for a target GSD of 2 cm using Equation 3-4 (resolved for Hg) and Equation 3-1 (resolved for D):

= 20 mm x 2 cm/(14.8 mm/2304) = 62.27 m which resulted in a much smaller area coverage of approximately 69 m by 46 m (see Fig. 9-15, yellow outline):

Dl = s x dL = (62.27 m/20 mm) x 22.2 mm = 69.12 m and

DW = s x dW = (62.27 m/20 mm)x 14.8 mm = 46.08 m navigation tolerance and space for covering the surrounding surface.

• Due to the elongated shape of the gully, an easily navigable platform (i.e., model airplane) for following the gully course is preferable to a more static tethered system.

• GCPs would have to be installed rather close to the gully edges to ensure their appearance on the photographs.

• As the gully is surrounded by arable land, GCPs cannot be expected to stay put for years, so we need to be prepared for renewing them for future surveys. At least four GCPs should be placed in potentially permanent positions to allow for restoring the reference system.

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