About – Reach Hydrographic Tools

Apriori Total Propagated Uncertainty (TPU) calculator & visualizer for hydrographic survey planning.

What this app does

This application helps hydrographic surveyors assess whether a proposed survey configuration meets required vertical and horizontal uncertainty specifications before going offshore. It implements apriori Total Propagated Uncertainty (TPU) calculations and compares them with permitted limits from selected standards (e.g., IHO S‑44). Results are shown as clear tables and graphs to highlight pass/fail status and the dominant error sources.

Use the TPU calculator via Apriori Total Propagated Error Calculations in the top navigation.

How it works

  1. User inputs: You specify instrument/system errors (static & dynamic), survey parameters (e.g., altitude/depth), reduction method (ellipsoidal or tidal), and the target standard.
  2. Computation engine: The backend combines component uncertainties using propagation of uncertainty (root‑sum‑of‑squares) to compute 1‑sigma (68%) and 2‑sigma (95%) totals for TVU and THU.
  3. Standards check: Computed totals are compared against permitted uncertainty from the selected standard (static and/or depth‑dependent terms).
  4. Visualization: Tables show component contributions and pass/fail; plots compare computed vs permitted values across altitudes/depths and include coverage, density, swath width, feature detection, and more.

How to use

  1. Open the TPU calculator: Go to Apriori Total Propagated Error Calculations.
  2. Complete the form: Enter realistic static and dynamic error values for each component (e.g., GNSS, motion, sound velocity, tide/ellipsoid). Select survey parameters and the required standard.
  3. Submit: Run the calculation to generate tables and plots.
  4. Review results: Check 1‑sigma and 2‑sigma totals versus permitted limits. Use the percentage contribution to identify dominant error sources.
  5. Iterate: Adjust inputs (e.g., better sensor specs, different altitude) and re‑run until the configuration meets requirements.

Other tools in this suite

Where to start

  • Gather manufacturer specs and recent calibration data.
  • Choose the correct standard/order (e.g., IHO S‑44 Order 1a or Special Order).
  • Set realistic survey altitudes/depths and line spacing goals.

Outputs explained

Tables

  • TVU vs Permitted: Lists each component with static/dynamic errors, % contribution, and 1‑sigma values per altitude, plus 1‑sigma & 2‑sigma totals and pass/fail cells for both the 68% and 95% checks.
  • THU vs Permitted: Same structure for horizontal uncertainty.
  • Inputs Table: Echoes all configuration values used for the run, for auditability.

Plots

  • TVU/THU vs permitted uncertainty (by altitude/depth).
  • Coverage, per‑beam, swath width, sounding spacing, density.
  • Feature detection curves (min/mean/max altitude scenarios).

Practical tips

  • Prefer measured calibration data over brochure values for critical components.
  • Use ellipsoidal reduction when appropriate; otherwise ensure tide model uncertainties are realistic.
  • Focus on components with the highest % contribution to reduce total uncertainty efficiently.

FAQ

1‑sigma is the combined standard uncertainty (≈68% confidence). 2‑sigma is ≈95% confidence; the app reports these and checks them against permitted limits.

From the standard you select (e.g., IHO S‑44). Limits may be static and/or depth‑dependent depending on the selected order.

Use the % contribution column to find dominant sources, improve those inputs (e.g., motion sensor accuracy, sound velocity control, survey altitude), and re‑run the analysis.

References