# Reflected GNSS signals gave aircraft height above ground within 4 m over flat terrain in a 288 km test flight

- Published: 2026-11-05 08:07 UTC
- Section: Sky & Space › Aviation
- Tags: GNSS reflectometry, height above ground level, aircraft altimetry, reflected satellite signals, Short-Time Shortest-Path, software-defined receiver, BeiDou Galileo GPS, Aurora SA60L, flight test Shandong, digital elevation model
- URL: https://realtech.media/news/rt-2d61762877c1601af0fb4602_reflected_gnss_signals/

**A Chinese team measured aircraft height above ground from reflected satellite signals on a 288 km flight, with accuracy better than 4 m over flat terrain and about 15 m in mountains.**

![Reflected GNSS signals gave aircraft height above ground within 4 m over flat terrain in a 288 km test flight](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/47bcfef2263716f6.jpg)
*European Space Agency, Wikimedia Commons, CC BY-SA 3.0 igo*

A joint team led by Professor Qin Weiwei of Rocket Force University of Engineering and Professor Xu Tianhe of Shandong University tested a way to measure aircraft altitude above ground level (AGL) with reflected satellite navigation signals. The study was published on 27 October 2026 in Satellite Navigation. The authors report accuracy better than 4 m over flat terrain and about 15 m in mountainous areas [1].

AGL is an important parameter for flight operations and safety. According to the paper, conventional measurement techniques depend on active signal transmission, are sensitive to environmental conditions, have limited coverage and use single-point geometry. The authors propose Global Navigation Satellite System Reflectometry (GNSS-R) as a complementary solution, based on comparing direct and surface-reflected signals [1].

## Flight test and equipment

The system used an upward-looking right-hand circular polarization antenna, a downward-looking left-hand circular polarization antenna and an intermediate-frequency collector for raw data. The data were processed offline with a software-defined receiver. The system was installed on an Aurora SA60L aircraft, which flew about 288 km from Dongying to Tai'an in Shandong Province, China [1].

Dual-frequency data were collected over rural, urban, suburban and mountainous terrain. The team used BeiDou B1C/B2a, GPS/QZSS L1 C/A/L5 and Galileo E1C/E5a signals to compute code-level path-delay differences between direct and reflected signals. According to the publisher's summary, the campaign gathered about 1.7 hours of raw data and tens of thousands of valid path-delay observations across 31 signal types [1].

## Short-Time Shortest-Path method

The authors propose the Short-Time Shortest-Path (STSP) method. It uses only 25 incoherent accumulations and selects the shortest path delay when the reflected waveform shows several peaks. Heavy averaging, by contrast, can smooth or distort waveforms reflected from land [1].

The GNSS-R results were compared with a reference built from precise GNSS positioning, a digital elevation model and a geoid model. Data availability was highest over flat rural areas, followed by undulating rural, urban/suburban and mountainous terrain. Wideband civil signals from BeiDou, Galileo and GPS/QZSS generally performed better than older or narrower-band ones, and Galileo E1C was the weakest. A higher cutoff elevation angle improved accuracy, especially in mountains, but reduced the number of usable observations. The authors say multipath and surface roughness dominate the remaining error [1].

The authors describe the system as an offline proof-of-concept platform. They say that before operational use, receivers must become smaller, lighter and capable of real-time processing, for example on GPU-based software-defined receivers [1].

## Sources

1. [Satellite Navigation](https://doi.org/10.1186/s43020-026-00228-6)
2. [EurekAlert](https://www.eurekalert.org/news-releases/1150278)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-2d61762877c1601af0fb4602_reflected_gnss_signals/