Question How Does Magnetometer Noise Vary with Sample Rate?
Topic starter 31/08/2023 8:59 am
Sensitivity is given as a frequency bandwidth product or nT/rt Hz RMS. This value is valid for ALL sample frequencies or sample rates.
Noise levels can also be given as Peak-to-Peak numbers at certain sample rates. For instance at 10 Hz.
- RMS value at 1 Hz for either instrument is approximately equal to the sensitivity
- P-P value at 1 Hz is roughly equal to 3x or 4x the RMS value. Remember that the Root Mean Square is not operating on a sine wave but on some random noise components as well and thus the actual Root Mean Square would be about 0.024nT for the 858 and 0.012 for the 882 at 1 Hz.
- For higher frequencies, we basically take the square root of the sample rate and multiply that times the P-P at 1 Hz. So for 10 Hz we have 0.075nT for the 858 and 0.036 for the 882. This is approximately what we see in the field and that can be verified (looking at the noise on an 882 in very quiet area, deep water, we see less than 0.050nT P-P.)
- So for 20 Hz the multiplier is 4.5 and for 40 Hz the multiplier is 6.3. So 882 noise at 40 Hz would be 6.3 x 0.012 = .075 nT P-P.