Forest height is an important indicator for the quality and quantity of forest resource. Polarimetric interferometric synthetic aperture radar (PolInSAR) technology has been demonstrated and validated as a potential way for forest height inversion and mapping in the last years. Indeed, air and spaceborne PolInSAR data has been applied in a variety of temperate, boreal, and tropical forest. However, since the effects of different microwave frequencies on forest scattering mechanisms and the different theory base of each estimation algorithm, uncertainties are obvious in forest height estimation and mapping using PolInSAR data. In order to clarify the uncertainties resulted from different microwave frequencies and selected algorithms in the procedure of forest height inversion, this paper discusses critical effects of the selected 4 inversion algorithms and 4 typical microwave length, using a simulated forest scene, on the performance of forest height estimation in a comprehensive way. The 4 inversion algorithms include Polarimetric phase center height estimation method (PPC), complex coherence phase center differencing algorithm (CCPCD), Coherence amplitude inversion method (CAI) and Hybrid inversion method. The involved microwave length are P, L, C and X band. The results demonstrate that the effects of the wavelength and estimation algorithm are obvious on the performance of forest height estimation using PolInSAR data. First, the selected estimation algorithm directly affects the accuracy of forest height estimation results when the microwave wavelength is same. The estimated results from CAI and Hybrid inversion methods agree well with the average forest height in the simulate forest scene at the 4 selected microwave bands, but values of the latter are slightly lower than the former. In addition, the estimated result of the former algorithm is more discrete with the maximum standard deviation value of 7.64 m, while the maximum standard deviation of the latter is 5.02 m. The uncertainty ratios of P、L、C and X are 0.918, 0.134, 0.293 and 0.278, respectively. The results reveal great underestimation of CCPCD method, especially HV channel phase was selected as the canopy scattering phase center and HH-VV phase was selected as the surface scattering phase center to retrieve the forest height. Second, the wavelength effects depend on the selected estimation algorithms. It shows no obvious effect on CAI method. However, it shows great effects on the performance of Hybrid inversion method. The estimation results from Hybrid inversion method show a better performance at long wavelength (P- and L- band), but a worse performance at short wave length (C- and X- band). HV PPC method show great underestimation on forest height at P-band, but it performs well in forest height estimation in other bands, notwithstanding a slightly underestimation. The uncertainties of estimation results depend on wavelength and algorithm selections. Short wavelength with CCPCD method and long wavelength with PPC method show better performance and the lowest uncertainties on forest height estimation. While CAI method shows the highest uncertainties in forest height estimation at P、C and X band. The conclusions demonstrated in the manuscript are obtained through a study of simulation data, where the forest scene is homogeneous and ideal, since the real forest has strong heterogeneity due to the influence of environment, forest type, structure, etc., it is necessary to further consider the effects on the selected estimation algorithms and wavelength resulted from the different forest scattering mechanisms affected by forest type, structure and so on. We will consider the related effects in the future research. © 2022 National Remote Sensing Bulletin. All rights reserved.
