Unité de mesure et interprétation

Is there anybody who can provide me and perhaps other user with a unit conversion table, explanation, etc… What is the difference between “EHZ” and “HDF” ? How can i know what my RS&B is measuring. What can i see in swarm, how to interpret graphics …
I see graph which says me micro/m/s and other one with frequencies (Hz). What are waves P and S. RS&B for dummy would be a great book for beginner like me.

Thanks a lot for your help

I had pretty much the same questions. There is a lot of answers to a lot of your questions on this website, but you do have to poke around to find it. I will give you what I know - if any of it is wrong, I am sure someone will be along to correct me.

Your RS&B has two transducers (measuring devices), one measures “infrasound”, that is, sound below the normal hearing range of humans. That is the HDF channel data. The other is the seismometer transducer, it measures movement in the vertical direction (the ‘Z’ axis), that is the EHZ channel data.

Both of these are sampled 100 times per second, the “count” data you see is the raw numbers from each of these. The device has some calibration data that can be downloaded. When you look at the data on the DataView web page that has used the calibration data to convert the count data to units appropriate to what is being measured (Air pressure for the infrasound channel, and micro-meters per second acceleration for the ground movement). In many ways, the units displayed are not very important for casual use. The graphs are the same, only the labeling changes.

For most things, the infrasound and accelerometer readings are independent, they are different things. However, there are some things that get picked up by both. The most common one you will probably see is a helicopter passing overhead. As you would expect, these usually give a very strong signal on the HDF channel. But most often, you will also see them register on the EHZ channe - yes, you were right in thinking that when one flys over your house, that it shakes the ground - it does!.

Look at the frequency graph of a helicopter pass, and you will see a quite distinctive ‘S’ curve, which is the doppler effect as it approaches and leaves. You can use the frequencies to determine the speed, if that is of interest to you.

If your location is like most, when you look at 24h of data, you will probably see a big difference between night and day. Look at the HDF data when there is a storm, or just wind blowing, and it will likely look very jagged as it picks up the air pressure differences caused by the wind gusts. It can also pick up remote thunder storms, windmills, and if you are lucky, and look carefully meteors passing overhead.

If you see an earthquake, it will probably have two signals separated by anything from a few seconds to minutes, depending on how far away it is. Those are the P and S waves. The P wave travels across the surface of the earth and arrives first (it is faster). The S wave travels through the earth, taking a longer route, and is slower. Knowing (roughly) the speed of each, you can use the gap between them to calculate how far away the earthquake was. Plot that as a circle on a map, then look at the same data on a different seismograph, same calculation but because it is likely a different distance away, the circle will be a different size and of course, a different origin when plotted. Use a third and where the three circles intersect is the location. Use more data from devices further around the earth, plot in 3-D and you get the depth of the event. Of course, computers do all the hard work for you, and you see the data on the StationView web page - your device is contributing to detection and locating those earthquakes.

Depending on how deep you want to get into P and S waves, there are some good articles available with a Google search.


A great thank for your explanation about the two mode of the RS&B, also taking your time to answer me with my questions. I understand a little bit more now. And I’ll be able to interpret with more accuracy what i see. But as i said, a complete “yellow for dummies” book could be a great idea for all users like me (Also RS&B pour les nuls… in french). I’m sure i’m not the only one who want to understand more that what we see. Not just only looking, but to be able to interpret, and perhaps help in case of catastrophe, I’m member of B-Ears network,“which is a HAM (radio amateur) alerting, helping, etc …(I’m only ONL)” in case of all other technology are down. I think that this kind of device could help us to be much more proactive. A collaboration with HAM radio amateur should be a good subject to discuss. Interface, automatic alerting, etc…

Sorry for my “brainstorming” on a Sunday afternoon on this subject, but i was thinking about all the advantage this kind of device could have and help people. Sieste maintenant, in french

Again thanks a lot for all


No problem. I had the same sort of experience, finding that this whole subject (well, set of subjects) is quite deep, and the more you learn, the more there is to learn. Like a lot of other subjects.

J’ai pense si je peux essayer de répondre en français (au moins 2 seconds…), mais ça fait 30 ans depuis que je vis en France…

Philip / K7UF


Vous avez raison, le sujet est vaste, et plus vaste est le sujet au fur et à mesure que l’on s’y plonge. J’espère que mes publications ne vont pas exaspérer la communauté des utilisateurs de RS, RS&B, etc. Je suis partant pour participer avec mes petits moyens intellectuel. Je crois qu’il ne s’agit pas uniquement de vendre. Il faut aussi fournir un soutien à la communauté. Voila, ce projet pourrais être fantastique. Partage d’info, techniques , scientifiques etc.


30 years in France and no word en français, that’s bad bro. Anyway, we have to do something to build a community for all owner of RS, RS&B , etc…

See you

Let’s re-phrase that … 30 SINCE I lived in France. That was for 10 years.
See how rusty my French has become :slight_smile:

I can’t (of course) speak for the RS team, but I do have the impression that they see the website a more than just a sales (and necessary tech support) site. The community has a complete range of expertise, from raw beginner to accomplished professional. The problem of trying to bring those together is that what is a new exciting discovery to someone like me is something that the professionals just see as very basic, and something that excites the professional may be way outside the capability of the new guy (me, for example) to understand without a lot of background research. The same problem occurs in all sorts of different areas.

Not that any of that should stop efforts to build/maintain the community that you envisage and share knowledge/experience – although that would mostly be in one direction. But not uniquely.