Relative photosynthetic activity of agricultural lands from airborne carbon dioxide and satellite data

Abstract

The relative net photosynthetic activity of crop, grass and woodland areas was estimated from airborne eddy correlation carbon dioxide flux density measurements for various transects within a 100 km by 300 km agricultural region in southern Manitoba. Landsat Multispectral Scanner (MSS) data were used to estimate the density and vegetation class boundaries associated with these measurements. The airborne carbon dioxide flux measurements were made during good growing conditions, namely with soil moisture reserves (> 50 per cent field capacity), high radiation (950 W/m²), cloudless skies and warm air temperature (> 25°C). The carbon dioxide flux ranged from (a) -20 to -35 kg CO₂ ha⁻¹ h⁻¹ for the heavy crop canopies of the cereal and oilseed growing areas located on the clay and clay loam soils, (b) -12 to -25kg CO₂ ha⁻¹ h⁻¹ for the mixed crop grassland and dense woodlands on loam to sandy loam soils and (c) -8 to - 15 kg CO₂ ha⁻¹ h⁻¹ for the mixed grassland areas on sandy loam to sandy soils. Indices calculated from Landsat bands 5 and 6 (red and near-infrared) were used to quantify the distribution of green vegetation. A large area relative photosynthetic index (LARPS), which is a measure of the carbon dioxide flux per vegetative greenness unit, is proposed as a parameter which represents the effectiveness of chlorophyll's ability to absorb carbon dioxide.