# Difference between revisions of "Radiolocation errors because of velocity variations"

(added page) |
(→Problem: add) |
||

Line 14: | Line 14: | ||

| isbn = ISBN 9781560801153 | | isbn = ISBN 9781560801153 | ||

}} | }} | ||

− | == Problem == | + | == 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? | 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? | ||

## Latest revision as of 15:36, 8 November 2019

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 |

## Contents

## 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 (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle V_{S}}**
be velocity over normal seawater and **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle V_{T}}**
velocity over other terrains. If we use **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle V_{S}}**
to calculate ranges, the error in range calculations will be **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \Delta x=t\left(V_{S} -V_{T} \right)}**
and the relative error is **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle \Delta x/x=1000\left(1-V_{T} /V_{S} \right)}**
m/km. When **Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle 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

Previous section | Next section |
---|---|

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