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Total Propagated Uncertainty (TPU) in Bathymetric Lidar

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dmariamp edited this page Jan 21, 2025 · 7 revisions

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Understanding Total Propagated Uncertainty (TPU)

Total Propagated Uncertainty (TPU) is critical in bathymetric lidar and remote sensing, especially in hydrographic surveying and mapping underwater terrains. This summary provides an overview of TPU, its importance, and applications, based on a presentation by Chris Parrish.

What is TPU?

TPU refers to the combined uncertainty from all sources in the measurement process and data processing workflow, including sensor parameters, environmental factors, and processing techniques. In the context of bathymetric lidar, which uses laser scanning to measure underwater topography, primary TPU component uncertainties include:

  • Subaerial Component: Sensor positioning, orientation, and in-air ranging (above water).
  • Subaqueous Component: Laser beam refraction at the air-water interface and scattering in the water column (below water).

Insert- TPU Components Diagram

Why is TPU Important?

Accurate measurement of underwater features is crucial for navigation, coastal management, and environmental monitoring. Understanding and minimizing TPU ensures the reliability and safety of these applications by:

  • Enhancing navigational safety through accurate depth measurements with robust uncertainty metadata.
  • Satisfying International Hydrographic Organization (IHO) requirements.
  • Supporting coastal zone management and decision-making (e.g., policy decisions related to modeled storm surge inundation).
  • Assessing the suitability of bathymetric data for various purposes.
  • Aiding environmental monitoring and assessment.
  • Enabling the comparison or combination of data from different technologies, systems, and/or epochs.

Components of TPU

  1. Subaerial Component (Analytical Uncertainty Propagation):

    • Involves uncertainties related to sensor parameters, scan angles, position and orientation (from post-processed GNSS/INS trajectory), and range measurements.
    • Analytical methods are used to propagate uncertainties from the airborne sensor to the water surface.
    • Formula for Subaerial Component: Includes the uncertainty in sensor positioning (e.g., roll, pitch, yaw uncertainties) and trajectory positional uncertainties.

  2. Subaqueous Component (Monte Carlo Ray Tracing):

    • Involves simulating the path of laser rays as they pass through the water column, considering refraction and scattering.
    • Monte Carlo simulations model the behavior of thousands of laser rays, providing a detailed uncertainty analysis.
    • Monte Carlo Simulation: Manages uncertainties due to water surface conditions (e.g., turbidity, wind speed) and laser beam scattering in the water.

Applications of TPU

TPU is applied in various domains, including:

  • Hydrographic Surveying: Accurate mapping of seafloor features to support marine navigation.
  • Coastal Mapping: Monitoring changes in shoreline and underwater topography.
  • Environmental Monitoring: Assessing habitats, sediment transport, and water quality.

Tools and Software

For practical tools, the cBLUE software provides a comprehensive solution for computing TPU in bathymetric lidar systems. It supports multiple lidar systems and offers features such as CSV export options, VDatum uncertainties, and a user-friendly interface for one-click processing.

Link to cBLUE GitHub Repository

Watch the Full Presentation

For a more detailed understanding, you can watch the full presentation by Chris Parrish on TPU in bathymetric lidar. The video covers in-depth explanations, visualizations, and real-world examples to help you grasp the concepts effectively.

Watch the Full Presentation on TPU

References

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