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The Vertical Challenge of Low-Altitude Economy: Why We Need a Unified Height System?

Shuaichen Yan, Xiao Hu, Jiayang Sun, Zeyuan Yang, Shipeng Li, Heung-Yeung Shum, Shijun Yin, Yuqing Tang

Abstract

The explosive growth of the low-altitude economy, driven by eVTOLs and UAVs, demands a unified digital infrastructure to ensure safety and scalability. However, the current aviation vertical references are dangerously fragmented: manned aviation relies on barometric pressure, cartography uses Mean Sea Level (MSL), and obstacle avoidance depends on Above Ground Level (AGL). This fragmentation creates significant ambiguity for autonomous systems and hinders cross-stakeholder interoperability. In this article, we propose Height Above Ellipsoid (HAE) as the standardized vertical reference for lower airspace. Unlike legacy systems prone to environmental drift and inconsistent datums, HAE provides a globally consistent, GNSS-native, and mathematically stable reference. We present a pragmatic bidirectional transformation framework to bridge HAE with legacy systems and demonstrate its efficacy through (1) real-world implementation in Shenzhen's partitioned airspace management, and (2) a probabilistic risk assessment driven by empirical flight logs from the PX4 ecosystem. Results show that transitioning to HAE reduces the required vertical separation minimum, effectively increasing dynamic airspace capacity while maintaining a target safety level. This work offers a roadmap for transitioning from analog height keeping to a digital-native vertical standard.

The Vertical Challenge of Low-Altitude Economy: Why We Need a Unified Height System?

Abstract

The explosive growth of the low-altitude economy, driven by eVTOLs and UAVs, demands a unified digital infrastructure to ensure safety and scalability. However, the current aviation vertical references are dangerously fragmented: manned aviation relies on barometric pressure, cartography uses Mean Sea Level (MSL), and obstacle avoidance depends on Above Ground Level (AGL). This fragmentation creates significant ambiguity for autonomous systems and hinders cross-stakeholder interoperability. In this article, we propose Height Above Ellipsoid (HAE) as the standardized vertical reference for lower airspace. Unlike legacy systems prone to environmental drift and inconsistent datums, HAE provides a globally consistent, GNSS-native, and mathematically stable reference. We present a pragmatic bidirectional transformation framework to bridge HAE with legacy systems and demonstrate its efficacy through (1) real-world implementation in Shenzhen's partitioned airspace management, and (2) a probabilistic risk assessment driven by empirical flight logs from the PX4 ecosystem. Results show that transitioning to HAE reduces the required vertical separation minimum, effectively increasing dynamic airspace capacity while maintaining a target safety level. This work offers a roadmap for transitioning from analog height keeping to a digital-native vertical standard.
Paper Structure (30 sections, 5 equations, 13 figures, 4 tables)

This paper contains 30 sections, 5 equations, 13 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Preliminaries
  3. Height Above Ellipsoid
  4. Height Above Mean Sea Level and Orthometric Height
  5. Height Above Ground Level
  6. Q-codes: QFE, QNH, and QNE
  7. Comparison of Height Systems
  8. The Fragmentation Problem: Why Current Systems Fail UAM?
  9. Multiple Stakeholders in Lower Airspace
  10. Challenges of Inconsistent Height Description and Missing Conversion Framework
  11. HAE: The Digital-Native Vertical Reference
  12. Criteria for an Ideal Lower Airspace Height System
  13. HAE: the Optimal Choice
  14. Digital Compatibility
  15. Reference Stability
  16. ...and 15 more sections

Figures (13)

  • Figure 1: Comparative Evaluation of Height Systems: Scale: 1 (lowest) to 4 (highest). Abbreviations: Ease for Conceptual simplicity, Stab. for Reference stability, Meas. Ease for Measurement practicality, Acc. for Measurement accuracy, and Appl. for Practical applications.
  • Figure 2: Illustration of de-facto height systems for LAE.
  • Figure 3: Atmospheric pressure obtained at Hong Kong International Airport from 1997 to 2024.
  • Figure 4: Height differences between various DEM datasets.
  • Figure 5: An overview of height system transformation framework.
  • ...and 8 more figures