Radiolocation errors because of velocity variations

**Problems in Exploration Seismology and their Solutions**
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?

**Table 7.1a. Radio-wave velocities over various terrains.**
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 $V_{S}$ be velocity over normal seawater and $V_{T}$ velocity over other terrains. If we use $V_{S}$ to calculate ranges, the error in range calculations will be $\Delta x=t\left(V_{S}-V_{T}\right)$ and the relative error is $\Delta x/x=1000\left(1-V_{T}/V_{S}\right)$ m/km. When $V_{T}<V_{S}$ , the error will be positive, meaning that the calculated range is too great. The results are shown in Table 7.1b.

**Table 7.1b. Location errors for various terrains.**
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
Table of Contents (book)

Also in this chapter

External links

find literature about
Radiolocation errors because of velocity variations