Global Mapping of Forest Vertical Structure with DQ-1 Multi-Wavelength LiDAR: Focus on Boreal Forests

Canopy percentile height is a critical parameter for describing forest vertical structure and assessing terrestrial carbon sequestration. At large scales, it is typically measured using spaceborne LiDAR systems. The DQ-1 satellite differs from conventional spaceborne LiDAR systems by employing a multi-band, single-footprint design with full-waveform reception, similar to ICESat-1 and GEDI. However, DQ-1 canopy height inversion is limited by 1064 nm waveform saturation and cross-band differences in shape and resolution. To overcome these issues, we propose a multi-band fusion algorithm (MBFA-F), whose resulting products serve as ancillary outputs of the DQ-1 satellite. Multi-source validation shows that with Finnish ALS data, MAE and RMSE remain small and stable in the RH20–RH40 range (MAE: 3.05–2.46 m; RMSE: 2.84–1.99 m). The errors increase with higher percentiles (RH41–RH100), reaching maximum values at RH100, where the MAE is 6.30 m and the RMSE is 4.89 m. With the combined use of ICESat-2 and GEDI data, RH98 yields an MAE of 6.27 m and an RMSE of 8.51 m, while RH90 yields an MAE of 6.40 m and an RMSE of 8.49 m. Although the accuracy may have some limitations, they effectively fill the data gap in high-latitude boreal forests, offering useful supplementary information for related research. Compared to the canopy percentile height products of GEDI and ICESat-2, statistical analysis of boreal forest regions shows that DQ-1 provides additional pixel coverage ranging from 0.05% to 3.06% in various countries. The above results demonstrate that the DQ-1 satellite has significant potential for dynamic monitoring of forest canopies.