Optical wireless sensor networks observe leaf phenology and photosynthetic radiation interception in a Brazilian tropical dry forest

Seasonally Dry Tropical Forest (SDTF) ecosystems are of great interest to earth observation sciences due to their strong influence over land-atmosphere exchange of carbon and water in semi-arid environments. Current space and airborne earth observation remote sensing platforms provide coarse temporal resolution and low signal to noise ratios in SDTF canopy phenology time series. In order to obtain hyper-temporal phenology information we present here a ground-based optical wireless sensor network (WSN) to monitor in-situ the seasonality of the forest canopy in a tropical dry forest reserve located in the Sao Francisco river basin in southeastern Brazil. In 2007 a network of hemispherical photosynthetically active radiation (PAR) sensors was deployed in the understory of a mature secondary SDTF to capture intercepted light at sub-hourly intervals and wirelessly transmit data to a central data aggregator. The resulting time series provides detailed information on the vegetative phenology, spatial variation of intercepted PAR (FIPAR), and growing season parameters.