Ping Sonar Altimeter used for measuring wave height

Blue Robotics Products Ping Sonar Devices
1

Hi there! I have a question about the “Ping Sonar Altimeter and Echosounder”, and its range. We are working on a rig that will be placed underwater at 30-40 m depth. This rig will be used to collect data from a range of sensors in order to measure the wave height above. As such, it will be stationary, and the Ping Sonar will point upwards to the water surface.

I have seen that the Ping Sonar has been used to measure tidal water level, but we want to use it to measure wave height at any given time. Anyone have experience with this? How about doing this at 30 m depth versus 40 m, is the written max range of 30 m a hard cut-off? Any advice here is greatly appreciated!

Thanks!

2

Hi Fred, welcome to the forum :slight_smile:

I don’t personally have experience doing this, but I imagine the main concern is the precision of the reading you get out. The ping sonar has a beam spread angle of 30 degrees, and a range resolution of 0.5% of the operating range (as per the product page technical details).

I’ve drawn up a quick sketch for roughly what this looks like:

image
image736×988 111 KB

The width of the beam at a target distance d is given by

w = 2d\cdot\tan{\left(\frac{\theta_b}{2}\right)}

where \theta_b = 30^{\text{o}}

For a depth of 30m the beam hits the surface as a roughly 16m diameter circle, with an intensity reading for every 15cm of depth. For 40m depth that diameter is 21.4m, with 20cm steps. Note also that most of the sound that the Ping emits doesn’t bounce back to where the device is, which is exacerbated by distance, and some sound is absorbed on the way to and from the target, so the returned sound reading is much less intense than the emitted sound.

The max range isn’t so much a hard cutoff as the furthest range we’re currently happy to stand behind in terms of expected result quality. Further distances are possible, but the low range resolution and the signal degradation due to noise, spread, and absorption means we can’t guarantee the sensor will perform as outstandingly as it does within the specified range limits.

The PingViewer application, which we provide as a way of viewing and interacting with the Ping devices, by default only allows reading the sonar at up to 30m of range, but it has a debug mode you can turn on which allows specifying up to 70m if you really want to.

Hope this is a useful explanation/clarification, and feel free to ask any follow-up questions if you’ve got them :slight_smile:

1 Like