How can I calibrate my instrument?
Read the calibration discussion.
What sampling rate should I use?
The maximum frequency you can hope to record is limited by a chain with 3 links: the maximum frequency of your seismic source, the maximum frequency your transmission channel (the earth) will carry, and the limits of your receiver. Let’s look at those 3:
- the seismic source may be band limited. An example is the vibroseis, as used by seismic prospection crews. For a vibroseis, the maximum frequency is defined by the sweep design. For example a typical modern sweep may vary between 4 and 80 Hz. On the other hand, an impulsive source (fracture mechanism like an earth quake), an airgun, dynamite or more simply a sledge hammer hitting the ground are broadband sources. An impulse (Dirac distribution) is supposed to carry all frequencies, from 0 to infinity. Real impulsive sources are indeed considered broadband.
- The earth acts as a low pass filter. Typically after 10s of travel through the earth, the highest frequency still available is less than 60 Hz, after 15s of travel less than 40Hz. Higher frequencies have been absorbed along the way. Geophysicist call this attenuation or Q, for quality factor. Since earthquakes are usually very distant events, they can be recorded with using relatively low frequencies.
- Electromagnetic geophones are limited on the high side by their spurious frequency (160Hz for the LF geophones, around 240Hz for the standard 10Hz phones). The recording system also has a maximum sampling frequency, defined by the electronic.
To decide on your sampling frequency find the weakest of the 3 links in the chain above, and let that define the maximum frequency you may be able to record. Then, the Nyquist theorem tells you your sampling frequency needs to be at least twice the maximum frequency you wish to record without aliasing. Practitioners usually choose a value about 20% higher than the Nyquist limit, to give themselves a bit of breathing room. Example, if you believe you may record events up to 60Hz of maximum frequency, Nyquist is 120 Hz for the sample rate, and you may settle on 150Hz of sample rate for your instrument.
How to find the polarity of a geophone?
Most geophones have the top plate clearly marked with a + and -. If not there is usually a 2mm diameter 1mm high cylindrical bump in the plastic on the side of the – contact. Last resort, connect to an oscilloscope (or to a functioning seisberry) and do a tap test.
How to format an SD card in ext4 (Linux partition) from a Raspebrry Pi?
The lsblk command lists information about all available or the specified block devices. It reads the sysfs filesystem and udev db to gather information.
Assuming the sd card is identified as /dev/sda, do the following. Please note that Linux partitions like ext4 need to be labeled msdos (weird and confusing). Also replace 64GB by the actual size of your card.
sudo parted /dev/sda mklabel msdos print free mkpart primary 0 64GB Ignore
Format, assuming a 64G card:
mkfs.ext4 -L 64G /dev/sda1
remove and put back to mount.
It is possible that you have to sudo the mkfs command. In that case, make sure user pi is the owner of the external media. If not:
sudo chown -R pi /media/pi/64G
What is a simple way to copy files to/from the Seisberry?
From a Windows, Mac or linux machine, open a terminal (called “command prompt” or simply “dos” in Windows). Then type:
and enter your password. Navigate your directories with cd and download files with “get”, upload files with “put”. Nothing to install, works on any computer, any OS. You may prefer to install an sftp client on your desktop.
Make the seisberry start recording at boot:
You can edit your crontab with:
Then add the following line to your crontab:
@reboot sleep 60 && cd /home/pi/Desktop/DIYSeis/C/ && ./ads1256_test param
I just made a new cool modification. How do I create and distribute an image?
I use some scripts called image-utils to create images of the Seisberry OS from the Seisberry itself, to a Micro-SD memory card plugged-in (which needs to be Linux formatted). For convenience the scrips are readily available in the “backup” directory on the desktop of the Seisberry. Read the read-me.txt in that directory then use the image-backup script to create an image of your OS in its current state. This image can be distributed, burnt to a new SD with Etcher and it will auto-expand to the new host Micro SD card size. This is how I clone my own Seisberries. If you do so, make sure your Seisberry “forgets” any WIFI password and reset your main password before and after cloning.
I recommand installing the Seisberry in a Pelicase, along with some desiccant beads (silica gel). It is possible to remove the valve of a pelicase and use the hole to run a power cable.
What are can I use my Seisberry for?
- Earthquake monitoring.
- Traffic count, discriminating between cars, heavy trucks, etc… without running any obstruction across the road.
- Train detection and count.
- Volcanology, volcanic tremor recording.
- Glacier movement recording.
- Rock fall monitoring and recording in mountainous area.
- Home monitoring.