GATE-2018 (24) :Wyllie – Time average equation

Q.59: - Magnetic survey was conducted from 8:00 to 12:00 noon and the following observations were recorded.

Station No	1 (Base)	2	3	4	5	1(Base)
Time	8:00	9:00	10:00	11:00	12:00	12:00
Total filed (ϒ) or (nT)	45500	45650	45750	45850	45850	45700

 

which station shows the maximum anomaly after linear drift correction?

 

Solution: -

 

This type of problems time is very important factor because, Gravity &Magnetic values varies with time that is called "Drift correction".

 

The difference between the first Base value and last Base value is 45700-45500=200 nT, normally Base values are always same but due to the effect of temperature and handling of the instrument reading will affect, so to minimise this effect using drift correction. (gamma=nT)

 

Total 4hours the change is=200nT

 

4*60*60s=200nT

 

1s=?

(s=seconds)

Magnetic anomaly(nT)for 1s=0.014 nT

 

Magnetic anomaly for 1 hour=50.4 nT

 

The anomaly variation from base to 2nd station=45,650-50.4=45,599.6nT

 

The anomaly variation from base to 3rd station=45,750-100.8=45,649.2nT

 

The anomaly variation from base to 4th station =45,850-151.2=45,698.8nT

 

The anomaly variation from base to 5th station=45,850-201.6=45,648.4nT

 

From the above information 4th station gives the maximum magnetic anomaly.