SEIS Seismometer Print

SEIS is a (very) broadband, very high resolution seismometer package, developed under PI-ship of Professor Philippe Lognonné at IPGP Paris.  It is based on a hybrid 4 axis instrument, composed of :

  • Two Very Broad Band (VBB) seismometers, in opposite sensing directions. These seismometers are based on an analog  feedback mass-spring mechanism; position of a capacitor sensor system is transferred back to the system via an (analog) Proportional Integrator system, passed to coils which re-centre the system to maintain a null position. The VBB seismometers are placed under vacuum in a titanium sphere to damp the daily temperature variations. The output of the seismometer is:
    • Seismometer  VBB “Velocity”, proportional to ground speed
    • Seismometer VBB “Position”, proportional to ground acceleration    
  • Two Short Period (SP) Micro Machined Electro-Mechanical System seismometers.  These seismometers are also based on feedback, but realized in an ultra-light, ultra-compact solution. The SP is sensitive to higher frequencies than the VBB. Output is “SP Velocity”.
  • A so-called “Scientific Temperature” sensor registers the outside temperature. This temperature recording is used in a correction procedure to re-centre the seismometers to compensate for to large diurnal temperature variations. 
  • Environmental sensors; temperature, pressure.
  • Deployment mechanism
  • SEIS Electronic “E-Box”, comprising
  • SEIS Acquisition and Control electronics including two SHAMROC ASICs and SEIS DC to DC converter electronics.
  • The E-Box is outside the titanium enclosure of the VBB seismometers and is thus exposed to the daily temperature variations on Mars. Inside the E-Box, temperature is regulated and therefore the electronics inside the box, including the SHAMROC ASICs, will in operation not experience temperatures beyond the range of -55 to +100 ˚C. 
  • Main performances requirements of the SEIS system are specified as follows:
  • VBB  noise <10-9 m.s-² Hz-½ from 10-3 up to 10 Hz
  • SP  noise < 5 10-8 m.s-² Hz-½ from 10-2 up to ~50 Hz

The measurement bandwidth of the VBB extends down to 10μHz in order to enable capturing the Phobos tide. Even though noise requirements are more relaxed at these low frequencies, it is the domain where electronic noise tends to rise rapidly, and design of the ASIC acquisition channels must be sufficiently “ smart”  in order to overcome the omnipresent “ 1/f noise”.