Forest stand biomass estimation using ALOS PALSAR data based on LiDAR-derived prior knowledge in the Qilian Mountain, western China

Abstract

Studies are needed to evaluate the ability of Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) for forest aboveground biomass (AGB) extraction in mountainous areas. In this article, forest biomass was estimated at plot and stand levels, and different biomass grades, respectively. Light detection and ranging (LiDAR) data with about one hit per m 2 were first used for forest biomass estimation at the plot level, with R 2 of 0.77. Then the LiDAR-derived biomass, as prior knowledge, was used to investigate the relationship between ALOS PALSAR data and biomass. The results showed that at each biomass level, the range of the back-scatter coefficient in HH and HV polarization (where H and V represent horizontal and vertical polarizations, respectively, and the first of the two letters refers to the transmission polarization and the second to the received polarization) was very large and there was no obvious relationship between the synthetic aperture radar (SAR) back-scatter coefficient and biomass at plot level. At stand level and in different biomass grades, the back-scatter coefficient increased with the increase of forest biomass, and a logarithm equation can be used to describe the relationship. The main reason may be that forest structure is complex at the plot level, while the average value could partly decrease the influence of forest structure at stand level. Meanwhile, terrain radiometric correction (TRC) was investigated and found effective for forest biomass estimation.

Mapping Canopy Height and Growing Stock Volume Using Airborne Lidar, ALOS PALSAR and Landsat ETM+

“…Such multi-annual SAR observations are of value for several reasons. In a series of publications, the benefit of using multi-temporal stacks of SAR intensity (in C-and L-band) for the retrieval of forest biophysical parameters has clearly been demonstrated [20,[30][31][32][33][34][35]. In addition, the multi-annual PALSAR acquisitions allowed for the computation of the interferometric repeat-pass coherence, which describes the temporal stability of scattering between two images and generally decreases with increasing forest density and height.…”

“…At a forest site in western Oregon, USA, Hudak et al [16] tested different spatial and aspatial methods for the extrapolation of small-footprint airborne Lidar estimates of canopy height by means of Landsat data. The synergy of Lidar and Synthetic Aperture Radar (SAR) has only been studied more recently [17][18][19][20]. The retrieval of forest aboveground biomass with multi-temporal and multi-polarization Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) L-band intensity and interferometric repeat-pass coherence data was tested by Sun et al [19] at a forested site in Maine using airborne large-footprint Lidar derived estimates of biomass for model calibration and validation.…”

“…Sun et al reported retrieval accuracies of 0.63 and 0.71 and 32.0 and 28.2 t/ha in terms of the R 2 and RMSE when using two polarimetric and dual-polarization PALSAR acquisitions, respectively. He et al [20] tested the retrieval of biomass at a mountainous forest site in southwestern China using three ALOS PALSAR dual-polarization acquisitions and airborne Lidar derived estimates of biomass for model calibration. At stand level, the retrieval accuracies for single images ranged from 0.67 to 0.79 in terms of the R 2 and improved further when using two PALSAR acquisitions jointly (R 2 of 0.84).…”

Improving the Estimation of Above Ground Biomass Using Dual Polarimetric PALSAR and ETM+ Data in the Hyrcanian Mountain Forest (Iran)

“…Thus, the joint usage of SAR and optical data for estimating AGB appears promising but still needs more investigation [6]. All of the mentioned studies were not in mountain forests probably because the estimation of forest structure parameters is strongly affected by the relief [5,[32][33][34][35]. Heterogeneous topography causes changes in backscattering mechanisms and induced large surface reflectance variations [5,36]; hence, topographic corrections are necessary for the minimization of such effects [6].…”

Characteristics of Decomposition Powers of L-Band Multi-Polarimetric SAR in Assessing Tree Growth of Industrial Plantation Forests in the Tropics

“…Polarimetric synthetic aperture radar (POLSAR) is an advanced technology that provides image data with phase (scattering matrix) information, which has made it a center of attention in recent years as an effective instrument for identifying land cover and estimating forest biomass [1][2][3][4][5][6][7].…”