ALOS PALSAR L-band polarimetric SAR data and in situ measurements for leaf area index assessment

Leaf area index (LAI), a key parameter controlling crop growth and yield models, has been widely estimated using optical satellite measurements. The estimation of LAI from high-resolution optical satellite data is limited by cloudy conditions and this may be a problem when systematic monitoring during the growing season is required. Synthetic Aperture Radar data are less susceptible to atmospheric effects than optical data and have been related to standing biomass over a number of landscapes. Here we quantify the relationship between LAI and both Advanced Land Observing Satellite (ALOS) Phased Array Synthetic Aperture Radar (PALSAR) L-band data and ENVISAT Advanced Synthetic Aperture Radar C-band data under relatively uniform soil moisture conditions. Digital hemispherical photographs were taken from large corn, soybean and pasture fields and forest plots on 4-5 July 2006 and processed using the CANEYE software to estimate in situ LAI. Estimates derived from PALSAR L-band polarimetric radar backscatter of crop (corn and soybean) fields and forest plots were in good agreement with measured LAI values, but the C-band Advanced Synthetic Aperture Radar imagery showed weak relationships. The study shows that PALSAR L-band polarimetric data have the potential to provide useful estimates of LAI, providing a possible alternative when optical data are limited by cloud cover. However, additional work is required to characterize the temporal variability of the relationship between PALSAR backscatter and LAI over varying soil moisture and soil surface conditions.