Towards the Operational Use of Satellite Hyperspectral Image Data for Mapping Nutrient Status and Fertilizer Requirements in Australian Plantation Forests

Abstract

EO-1/Hyperion data can potentially reduce the cost of nutrition assessments in plantation forests, supplementing standard point-based measurements with comprehensive and repeated broad-acre coverage. We present a synopsis of studies using EO-1/Hyperion data for foliar nutrition assessments in Australia. The earliest study compared modeling methods and calculated models in the order of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.7 for Nitrogen, Phosphorus and Boron in Eucalyptus and Pinus species. Several recommendations of that work were adopted in a subsequent project which concluded that observing stand structure may improve nutrient prediction models calibrated from image data over those calibrated from laboratory spectra. The most recent study examined the range of age classes over which nutrients could be accurately predicted in P. radiata from Hyperion images. Canopy cover fraction, calculated using spectral mixture analysis, ranged from 69% in unthinned 5 year old stands to 43% and 41% in stands 10 to 20 years old that had been thinned once or twice respectively. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> value when predicting Nitrogen across all age classes was 0.45 increasing to 0.87 when calibrated on only the 5 year old trees. Collectively, these studies demonstrate that several important nutrients can be accurately mapped from Hyperion data at ages that are critical for the management of plantation forests. However, some of Hyperion's spatial and radiometric characteristics limit its practical operational application. This manuscript discusses potential improvements that might be provided by the HyspIRI mission, and the key challenges in developing hyperspectral image data as an operational tool for forest nutrition assessments in Australia.