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Separation of Overlapped Direct and Reflected Waveforms for Low-Altitude UAV-Based GNSS-R Altimetry.

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Title: Separation of Overlapped Direct and Reflected Waveforms for Low-Altitude UAV-Based GNSS-R Altimetry.
Authors: Xu, Ziyin1,2,3 (AUTHOR), Wang, Xianyi1,2,3 (AUTHOR) wxy@nssc.ac.cn, Xia, Junming1,2,3 (AUTHOR), Sun, Yueqiang1,2,3 (AUTHOR), Liu, Cheng1,2,3 (AUTHOR), Wang, Zhuoyan1,2,3 (AUTHOR), Tian, Yusen1,2,3 (AUTHOR), Qiu, Tongsheng1,2,3 (AUTHOR), Wang, Dongwei1,2,3 (AUTHOR)
Source: Remote Sensing. Mar2026, Vol. 18 Issue 6, p893. 25p.
Subjects: Signal separation, Altitude measurements, Global Positioning System, Interference (Telecommunication), Remote sensing
Abstract: Highlights: What are the main findings? A GNSS-R altimetry algorithm based on signal separation is proposed to address direct and reflected signal mixing in low-altitude UAV observations. The direct-signal-priority strategy suppresses the dominant direct signal and retrieves the geometric delay, enabling stable real-time height estimation. What are the implications of the main findings? The proposed method improves the robustness of GNSS-R altimetry under strong signal coupling conditions typical of low-altitude platforms. The results support the application of UAV-based GNSS-R for rapid surface elevation monitoring and inland water observation. GNSS reflectometry (GNSS-R) altimetry has been widely used for retrieving surface elevation over oceans, cryosphere, and land. Recently, UAV-borne GNSS-R systems have gained attention due to their flexibility for low-altitude and localized observations. However, lightweight UAV platforms impose strict payload and real-time processing constraints. At low altitudes, the small geometric delay between direct and reflected signals often leads to waveform overlap, degrading conventional altimetry algorithms. In this study, a lightweight UAV-borne GNSS-R receiver and a signal-separation-based altimetry method are proposed. Direct and reflected signals are separated using waveform characteristics without relying on external height information, mitigating the impact of waveform overlap. Simulations and experiments using a SPIRENT 9000 GNSS simulator demonstrate stable height retrieval under dynamic low-altitude conditions while maintaining real-time capability, confirming the feasibility of lightweight UAV GNSS-R altimetry for rapid elevation monitoring. [ABSTRACT FROM AUTHOR]
Copyright of Remote Sensing is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Separation of Overlapped Direct and Reflected Waveforms for Low-Altitude UAV-Based GNSS-R Altimetry.
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  Data: <searchLink fieldCode="AR" term="%22Xu%2C+Ziyin%22">Xu, Ziyin</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Wang%2C+Xianyi%22">Wang, Xianyi</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<i> wxy@nssc.ac.cn</i><br /><searchLink fieldCode="AR" term="%22Xia%2C+Junming%22">Xia, Junming</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Sun%2C+Yueqiang%22">Sun, Yueqiang</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Liu%2C+Cheng%22">Liu, Cheng</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Wang%2C+Zhuoyan%22">Wang, Zhuoyan</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Tian%2C+Yusen%22">Tian, Yusen</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Qiu%2C+Tongsheng%22">Qiu, Tongsheng</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Wang%2C+Dongwei%22">Wang, Dongwei</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Remote+Sensing%22">Remote Sensing</searchLink>. Mar2026, Vol. 18 Issue 6, p893. 25p.
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  Data: <searchLink fieldCode="DE" term="%22Signal+separation%22">Signal separation</searchLink><br /><searchLink fieldCode="DE" term="%22Altitude+measurements%22">Altitude measurements</searchLink><br /><searchLink fieldCode="DE" term="%22Global+Positioning+System%22">Global Positioning System</searchLink><br /><searchLink fieldCode="DE" term="%22Interference+%28Telecommunication%29%22">Interference (Telecommunication)</searchLink><br /><searchLink fieldCode="DE" term="%22Remote+sensing%22">Remote sensing</searchLink>
– Name: Abstract
  Label: Abstract
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  Data: Highlights: What are the main findings? A GNSS-R altimetry algorithm based on signal separation is proposed to address direct and reflected signal mixing in low-altitude UAV observations. The direct-signal-priority strategy suppresses the dominant direct signal and retrieves the geometric delay, enabling stable real-time height estimation. What are the implications of the main findings? The proposed method improves the robustness of GNSS-R altimetry under strong signal coupling conditions typical of low-altitude platforms. The results support the application of UAV-based GNSS-R for rapid surface elevation monitoring and inland water observation. GNSS reflectometry (GNSS-R) altimetry has been widely used for retrieving surface elevation over oceans, cryosphere, and land. Recently, UAV-borne GNSS-R systems have gained attention due to their flexibility for low-altitude and localized observations. However, lightweight UAV platforms impose strict payload and real-time processing constraints. At low altitudes, the small geometric delay between direct and reflected signals often leads to waveform overlap, degrading conventional altimetry algorithms. In this study, a lightweight UAV-borne GNSS-R receiver and a signal-separation-based altimetry method are proposed. Direct and reflected signals are separated using waveform characteristics without relying on external height information, mitigating the impact of waveform overlap. Simulations and experiments using a SPIRENT 9000 GNSS simulator demonstrate stable height retrieval under dynamic low-altitude conditions while maintaining real-time capability, confirming the feasibility of lightweight UAV GNSS-R altimetry for rapid elevation monitoring. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of Remote Sensing is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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      – SubjectFull: Altitude measurements
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              Text: Mar2026
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