Sub-Canopy Topography Estimation from TanDEM-X DEM by Fusing ALOS-2 PARSAR-2 InSAR Coherence and GEDI Data

Zhiwei Liu,Haiqiang Fu,Jianjun Zhu,Changcheng Wang,Pengyuan Tan,Chen Zhang

doi:10.3390/s20247304

Abstract

This paper develops a framework for extracting sub-canopy topography from the TanDEM-X digital elevation model (DEM) by fusing ALOS-2 PARSAR-2 interferometric synthetic aperture radar (InSAR) coherence and Global Ecosystem Dynamics Investigation (GEDI) data. The main idea of this method is to estimate the forest height signals caused by the limited penetration of the X-band into the canopy from the TanDEM-X DEM. To achieve this goal, a spaceborne repeat-pass InSAR coherent scattering model is first used to estimate the forest height by the ALOS-2 PARSAR-2 InSAR coherence (APIC), taking the GEDI canopy height as the reference. Then, a linear regression model of the TanDEM-X DEM Vegetation Bias (TDVB) depending on the forest height and the fraction of vegetation cover (FVC) is established and used to estimate the sub-canopy topography. The proposed method was validated by the data of the Amazon rainforest and a boreal forest in Canada. The results showed that the proposed method extracted the sub-canopy topography at the study sites in the tropical forest and boreal forest with the root mean square error of 4.0 m and 6.33 m, respectively, and improved the TanDEM-X DEM accuracy by 75.7% and 39.7%, respectively.

Highlights

Digital Elevation Model (DEM) describing the shape of “bare-earth” plays an important role in various applications, such as hazard monitoring, flooding prediction, resource management [1,2,3].Interferometric synthetic aperture radar (InSAR), an active remote sensing technology, has been demonstrated to be a powerful tool for mapping large-scale, high-resolution, and high-precision topography [4,5,6,7]
The ALOS-2 PARSAR-2 InSAR coherence (APIC) data was collected by the Japan Aerospace Exploration Agency (JAXA) in dual polarization (HV and HH) on 12 March and 26 March 2015
We have demonstrated that the TanDEM-X DEM contains non-negligible forest height signals that contaminate real terrain information in forest areas, especially tropical rainforests

Summary

Introduction

Digital Elevation Model (DEM) describing the shape of “bare-earth” plays an important role in various applications, such as hazard monitoring, flooding prediction, resource management [1,2,3].Interferometric synthetic aperture radar (InSAR), an active remote sensing technology, has been demonstrated to be a powerful tool for mapping large-scale, high-resolution, and high-precision topography [4,5,6,7]. InSAR system TerraSAR-X/TanDEM-X with X-band, and it has high accuracy and good global consistency [8,9,10]. It cannot reflect the sub-canopy topography because the X-band SAR signal has poor penetration in the forest layer, resulting in the TerraSAR-X/TanDEM-X InSAR (TSX/TDXI). The TanDEM-X DEM over forests cannot be used directly in many applications. The TSX/TDXI system mainly works with single-baseline and single-polarization configurations, so it cannot separate the volume scattering and ground scattering contributions [14,15].

Objectives

Methods

Results

Discussion

Conclusion