High-resolution remote sensing of intertidal ecosystems: A low-cost technique to link scale-dependent patterns and processes

Guichard, Frédéric, Edwin Bourget, Jean-Paul Agnard

Limnol. Oceanogr., 45(2), 2000, 328-338 | DOI: 10.4319/lo.2000.45.2.0328

ABSTRACT: Linking experimentally tested local processes to natural patterns in intertidal ecosystems requires data-acquisition techniques that provide spatiotemporal data from the scale of local processes to the scale of patterns. We developed a low-cost, high-resolution remote-sensing technique based on the use of a 6-m helium-inflated blimp, a standard 35-mm camera, and photogrammetric numerical tools in order to acquire high-resolution data of environmental (i.e.,\ topographic) and biological (i.e., algal biomass) variables over intertidal landscapes. The camera was calibrated for photogrammetric analysis, and overlapping color aerial photographs were taken at an altitude of 80 and 50 m. We performed stereo analysis of digitized images and numeric topographic restitution over an 18 3 18 m area with an error of 0.02 m along the Z axis. A normalized vegetation index (NDVI) from color-infrared images at 0.02-m resolution over the same area was computed. Algal biomass sampled within the photographed area allowed us to calibrate NDVI with algal biomass (R2 = 0.73, p < 0.01). Aggregation analysis performed on a height above zero level, local topographic heterogeneity, and algal biomass confirmed, at the landscape level, previous local experi-mental evidence of a relationship between topographic heterogeneity and algal biomass increasing from scales of 0.5 to 2 m. Our method permits multiscale testing of local scale-dependent processes over a natural landscape.

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