GNSS Positioning Environment Assessment in Urban Rivers for Autonomous Boats using Polarimetric SAR data
Takuto Nagaoka(a*), Kyogo Noda(a), Tetsu Yamaguchi(a), Nobuaki Kudo(b), Etsuro Shimizu(b), Masahumi Nakagawa(a)

a) Shibaura Institute of Technology, Japan
*ah22021[at]shibaura-it.ac.jp
b) Tokyo University of Marine Science and Technology, Japan

Abstract

The increasing growing need for autonomous boat navigation on urban rivers has revealed a major challenge: the substantial reduction in Global Navigation Satellite System (GNSS) accuracy caused by surrounding high-rise buildings and bridges. To ensure safe autonomous navigation requires, identifying non-GNSS areas by assessing the positioning environment over a wide area, however, conventional methods lack efficiency and spatial coverage. This study proposes a novel method of estimating the GNSS positioning environment over a wide area using full-polarimetric synthetic aperture radar (SAR) data. We validated its effectiveness using in-situ data from a waterborne mobile mapping system (MMS). We used ALOS-2/PALSAR-2 data and applied, Pauli decomposition to classify microwave scattering mechanisms as surface, double-bounce, or volume scattering. We hypothesized that surface scattering would correspond to favorable GNSS conditions, while double-bounce and volume scattering would indicate poor environments prone to multipath and signal blockage. To validate the estimation, we conducted a qualitative analysis by comparing the Pauli decomposition results with three data sources: 1) 3D point clouds acquired by the waterborne MMS, 2) the 3D city model(Project PLATEAU), and 3) the measured GNSS positioning solutions (RTK-FIX/FLOAT). The analysis revealed a strong correlation between the SAR-derived scattering map and the actual GNSS performance. Specifically, open sky areas such as the Shiomi canal exhibited surface scattering and stable RTK-FIX solutions. In contrast, the sections of the Nihonbashi River under the expressway were dominated by double-bounce and volume scattering, resulting in unstable RTK-FLOAT solutions. This study demonstrates that Pauli decomposition of polarimetric SAR data can effectively evaluate the GNSS positioning environment across an entire area. These results can be applied to optimize navigation routes and generate positioning environment maps to enable seamless switching between GNSS and non-GNSS positioning.

Keywords: SAR, ALOS, RTK-GNSS, waterborne MMS

Topic: Topic B: Applications of Remote Sensing