Vegetation height estimates for a mixed temperate forest using satellite laser altimetry

Abstract

Data from the Geoscience Laser Altimeter System (GLAS) aboard the Ice Cloud and land Elevation Satellite (ICESat) offer an unprecedented opportunity for canopy height retrieval at a regional to global scale. The data also provide useful information for forest stand level assessment at coincident locations. In this study height indices from light detection and ranging (LiDAR) waveforms were explored as a means of extracting canopy height; these were examined with reference to a mixed temperate forest in Gloucestershire, UK, containing planted stands with a mean age of 51 years and mean maximum height of 26.6 m. A method based on using a terrain index (TI; maximum minus minimum elevations from a 767 subset 10-m resolution digital terrain model (DTM)) to adjust the waveform extent (WE; signal begin minus signal end) produced an R 2 value of 0.89 when regressed against field measurements of maximum canopy height at footprint locations (field height50.91(WE2TI) + 4.86; root mean squared error (RMSE)52.99 m, coefficient significance p,0.001, intercept significance p.0.01). Multiple regression performed on both WE and TI with field measurements produced an R 2 of 0.90 and an RMSE of 2.86 m (field height51.0208WE20.7310TI; coefficient significance p,0.001, intercept not significant). Maximum canopy height estimates using an automated approach to ground return identification based on iterative fitting of Gaussian peaks (GP1_2 MAXAMP ) to the waveform explained 74% of variance when compared to field measurements (field height51.05(GP1_2 MAXAMP ); RMSE54.53 m, coefficient significance p,0.001, intercept not significant). The ability of satellite LiDAR to retrieve data for such a complex and diverse area further indicates the potential of this technique for both carbon accounting and forest management.

Model effects on GLAS-based regional estimates of forest biomass and carbon

“…This apparent increase in area-based volume estimates suggests that steeper slopes broaden the waveform response, increasing apparent canopy height and inflating the volume estimates. Slopes, as noted by Lefsky et al (2005Lefsky et al ( , 2007 and Rosette et al (2008), negatively affect the height accuracy of the largefootprint GLAS waveform data, convolving forest-canopy architecture with topography, and increasing the vertical extent of the waveform. The tangent of the actual topographic slope multiplied by the GLAS footprint diameter provides an upper limit to the vertical pulse broadening expected due to slope (Lefsky et al 2007;A.…”

“…Sun et al (2008) compare various GLAS height metrics to coincident airborne LiDAR estimates and report RMSEs of 3-5.5 m (their table 2) in the temperate forests of the eastern US. Rosette et al (2008) report ground-GLAS height RMSEs of 2.86 m after correcting for topography. Lefsky et al (2005) report RMSEs associated with ground-GLAS maximum canopy-height comparisons of ,4.5 m, and Lefsky et al (2007), after correcting for local topography using trailing-edge measures, illustrate an RMSE of 5 m across diverse study sites in their figure 3.…”

Forest Canopy Height Estimation from Calipso Lidar Measurement

“…Several canopy height models from GLAS waveforms have been developed in recent years depending on different parameters retrieved from full waveforms and ancillary DEM data [8][9][10][11]. The GLAS-derived canopy height within each footprint has a precision between 2 and 13 m depending on forest types and characteristics of the study site.…”

“…Many researchers have studied the forest canopy height globally from large footprint spaceborne lidars [3][4][5][6][7]. For example, the Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (ICESat) provides forest canopy height from the full waveform data [8][9][10][11].…”

Estimating Canopy Gap Fraction Using ICESat GLAS within Australian Forest Ecosystems

“…This becomes particularly challenging when attempting analyses over complex terrain [33]. In an attempt to mitigate the influence of complex terrain, we employ the method of Rosette et al [34] to locate the 'ground' in returned GLAS waveforms. This method makes use of the (up to 6) fitted Gaussians that form the model alternate return pulse, where the ground is considered to correspond to the centre of the Gaussian that exhibits the greatest amplitude of the two that are least elevated within the waveform (Figure 2b).…”