Radiolocation errors because of velocity variations
 | |
| Series | Geophysical References Series |
|---|---|
| Title | Problems in Exploration Seismology and their Solutions |
| Author | Lloyd P. Geldart and Robert E. Sheriff |
| Chapter | 7 |
| Pages | 221 - 252 |
| DOI | http://dx.doi.org/10.1190/1.9781560801733 |
| ISBN | ISBN 9781560801153 |
| Store | SEG Online Store |
Problem 7.1
Ground conductivity affects radio-wave velocity because of currents induced in the earth. Range calculations assuming that travel is over normal seawater thus may be in error if this is not true. What errors are involved for travelpaths over the terrains in Table 7.1a?
| Terrain | Velocity (km/s) |
|---|---|
| Seawater | 299 670 |
| Freshwater | 299 250 |
| Farmland | 299 400 |
| Dry sand | 299 900 |
| Mountains | 298 800 |
Background
Radio-navigation methods are used to determine distances in marine surveys and the velocity is generally assumed to be that over saltwater.
Solution
Let Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): V_{S} be velocity over normal seawater and Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): V_{T} velocity over other terrains. If we use Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): V_{S} to calculate ranges, the error in range calculations will be Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): \Delta x=t\left(V_{S} -V_{T} \right) and the relative error is Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): \Delta x/x=1000\left(1-V_{T} /V_{S} \right) m/km. When Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): V_{T} <V_{S} , the error will be positive, meaning that the calculated range is too great. The results are shown in Table 7.1b.
| Terrain | Velocity (km/s) | Error (m/km) |
|---|---|---|
| Seawater | 299 670 | 0.0 |
| Freshwater | 299 250 | 1.4 |
| Farmland | 299 400 | 0.9 |
| Dry sand | 299 900 | –0.8 |
| Mountains | 298 800 | 2.9 |
Continue reading
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|---|---|
| Improvement of signal/noise ratio by stacking | Effect of station angle on location errors |
| Previous chapter | Next chapter |
| Characteristics of seismic events | Reflection field methods |
Also in this chapter
- Radiolocation errors because of velocity variations
- Effect of station angle on location errors
- Transit satellite navigation
- Effective penetration of profiler sources
- Directivity of linear sources
- Sosie method
- Energy from an air-gun array
- Dominant frequencies of marine sources
- Effect of coil inductance on geophone equation
- Streamer feathering due to cross-currents
- Filtering effect of geophones and amplifiers
- Filter effects on waveshape
- Effect of filtering on event picking
- Binary numbers
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