A personal RP-33 teaching aid

Not PC-IMAT

Tap the map to choose a water point You’ll confirm the point before the profile loads.
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Three short lessons · about 8 minutes total

See the profile, then follow the sound.

Start with the water column, connect its shape to the path families, then compare how location and time of year reshape the upper ocean.

Lesson 01

Read the sound-speed profile

About this project

Built to make one difficult idea visible.

Not PC-IMAT is an independent teaching aid that connects a public-climatology sound-speed profile at a selected map point to an idealized, range-independent acoustic ray picture.

Creators

LT Sean Egan, PhD United States Navy · Created for fellow METOC officers and Aerographer’s Mates.

sean@theinformed.org

How it was made

Python processes and packages the environmental data; FastAPI serves compact profile requests; Leaflet displays self-hosted terrain tiles; browser-native SVG and Canvas draw the teaching views; and Manim renders the narrated lessons.

WOA23 supplies temperature and practical salinity. Pressure and sound speed are calculated from depth and latitude with TEOS-10/GSW.

Sources and methods

RP-33 library record Navy underwater acoustics · Chapter 8 Urick · Sound Propagation in the Sea WOA23 climatology GEBCO_2026 terrain Seafloor sediments

Terrain: GEBCO Bathymetric Compilation Group 2026 (2026), The GEBCO_2026 Grid, doi:10.5285/4f68d5c7-45eb-f999-e063-7086abc036fa.

Independent educational project, built by us on our own time. The views expressed here are ours alone and do not reflect the official policy or position of the U.S. Navy, the Department of War / Department of Defense, or the U.S. Government, nor do we represent them. This site is intended for learning, not operations—do not use it for operational decisions; use it at your own risk. Not an acoustic prediction or navigation aid.

Display aid · not predicted received level

Ray-display fading—not a propagation-loss prediction

Opacity uses a fixed spherical-spreading proxy based on horizontal range, simplified absorption along the traced path, and fixed penalties at surface and ocean-floor contacts.

TLrel = 20 ⁢ log10 ( RR0 ) + α ⁢ s + ∑i Li

Current trace settings will appear after a point is plotted.

TLrel
A relative display value, in decibels. A larger value draws the ray more faintly; it is not predicted transmission loss at a receiver.
R
Horizontal range from the source—not distance traveled along the ray.
R0
The 1 m reference range.
s
Cumulative distance traveled along the ray path, in kilometers.
α
Absorption in dB/km at the current frequency.
∑i Li
The sum of the fixed surface and ocean-floor contact-loss presets. Real boundary loss depends on frequency, grazing angle, roughness, sediment, and sub-bottom structure.

This display omits focusing, interference, diffraction, scattering, duct leakage, and received level. A ray disappearing at the drawing cutoff does not mean the physical sound stops there. It is not detection probability or an operational sonar equation.