1. Wind-Noise Abatement for 3-C Geophones
Henry Bland and Eric Gallant
Photo: National Weather Service Office Cheyenne, Wyoming. wy.skywarn.net

2. The Problem Noisy seismic on windy days
Geophone arrays are rare for 3-C seismic surveys
Good SNR: Vertical data Bad SNR: Horizontal data

3. Henry with anemometers
An experiment was performed in which geophones were placed in a windy field. We monitored the noise from the geophones with a small portable seismic recorder. Geophones were grouped in a 20m x 12m patch. The patch extends from the truck to where I am kneeling. Three anemometers were spread around the edges of the patch. A computer records the wind speed from the anemometers and correlates it to the shot records.
Henry with anemometers

4. Geophones were buried in holes. This one was 45cm deep
Geophones were buried in holes. This one was 45cm deep. It took about 8-10 minutes to dig by hand.
Digging a hole

5. Without using a planting pole, it’s difficult to plant a geophone in a deep hole. Here Eric Gallant is planting and leveling a 3-C geophone in a 45cm deep hole.
Planting a geophone

6. Apparatus Digital Anemometer Notebook computer Weather data network
Trigger
signal
Test patch of geophones
Seismic data recorder
(Geometrics Strataview R60)
Apparatus

7. Flow chart Fold low? Find m, s, Speed 1 bin = m/(0.5km/h) Speed 2 No
Wind Noise Experiment
Find m, s,
bin = m/(0.5km/h)
Speed 1
Speed 2
Fold low? No
Speed 3
Yes
Wind constant? No No
This is a flowchart showing the PC acquisition program’s logic.
Yes
Got fold
for all values of m?
Trigger
& Log m, s
Yes
Finish
Flow chart

8. Wind noise appears to increase from left to right
Wind noise appears to increase from left to right. Wind speed increases from left to right.
Raw record

9. If we look at a number of traces from a single geophone in the frequency domain, we see that wind noise (areas of darkness) increases consistently as the wind speed increases. We also get a sense of the signal band of the wind noise from this spectrograph.
Spectrograph

10. Data shown are from a vertical element at a single geophone
Data shown are from a vertical element at a single geophone. Note that SNR decreases by about 1dB per 1hm/h of wind speed.
SNR vs Speed

11. Geophones at different depths
Geophones were buried at different depths. Some were left uncovered, while others were covered with soil.
Geophones at different depths

12. Vertical Component
Depth (cm) 5 10 13 19 20 23 24 26 48

13. In-line Component
Depth (cm) 5 10 13 19 20 23 24 26 48

14. Cross-line Component
Depth (cm) 5 10 13 19 20 23 24 26 48

15. Signal to noise ratio (dB)
Results: Vertical
3 dB
10 cm
Signal to noise ratio (dB)
The line shows the fit of the covered geophones. SNR improves by 3dB for every 10cm of burial depth.
Geophone depth (cm)

16. Signal to noise ratio (dB)
Results: Horizontal
3 dB
10 cm
Signal to noise ratio (dB)
Same trend for horizontal elements, though the intercept is 3dB down. This means that horizontal elements are more susceptible to wind noise.
Geophone depth (cm)

17. Conclusions We can measure wind noise and relate it to wind speed
Wind noise increases by 1 db per km/h (wind speed 30cm above ground level)
Wind noise decreases by 3 db per 10 cm of geophone depth
For each 3 km/h of additional wind speed, bury geophones 10cm deeper to maintain the same SNR

18. Acknowledgements Anemometer and cows Malcolm Bertram Peter Cary
Kevin Hall
Don Lawton
Robert Stewart
Our valued CREWES sponsors
Anemometer and cows