Optical remote sensing of forest leaf area index and biomass

Abstract

Forests are the most complex terrestrial ecosystem on Earth’s land surface, providing vital goods and services upon which the welfare of humanity depends. The quantification of leaves and biomass in forests is critical for understanding the ecological role of forests in the terrestrial ecosystem. Great effort has been dedicated to the mapping of leaf area and biomass using remotely sensed data. This review focuses on the use of optical remote sensing in mapping leaf area index (LAI) and aboveground biomass for forests. Significant progress has been made in mapping LAI in the past few decades. Mapping of LAI started with location-specific empirical approaches and evolved to semi-empirical and biophysical approaches, which can be applied globally. Although there are some biases in the current LAI products, it can be expected that better-quality LAI products will be delivered in the future. At present, mapping biomass remains predominantly empirical because there is no direct physical relationship between reflected energy in visible, near or mid infrared wavelengths and biomass. Mapping biomass relies on the explicit or implicit mapping of forest structural parameters that are related to biomass allometrically. Although optical images have been successfully used in mapping biomass in low biomass areas, it remains a challenge to map biomass in forested areas with high biomass density due to signal saturation.