# Homework Help: How we measure magnetic disturbances?

1. Feb 25, 2013

### stavrospao

Due to a homework,i want to measure "ΔBy" component with low orbit satellites,so i can measure Birkeland currents.Does anyone Know how to do it?For example i use the equation J=0.1ΔΒy/Δt.What should magnetometers data measure?Do they measure ΔBy or some other indicator that associates with By?If so,how this associates with By?(It would be too time consuming for me to search for it on the internet because of my English level).Thanks very much.

2. Feb 27, 2013

### marcusl

Can you explain what ΔBy is? The Δ implies it is a difference in the y component of magnetic field with respect to something, but what? Are you trying to compute the time derivative dBy/dt?

3. Feb 28, 2013

### stavrospao

First of all thanks for the reply.Secondly,I made a wrong..I want to measure By component(not ΔBy as i mentioned).I gave you the formula(J=0.1ΔΒy/Δt)..I think this is what i try to measure(dBy/dt,Δ is like d..)but i don't know how to do it..

Last edited: Feb 28, 2013
4. Feb 28, 2013

### marcusl

You want to use a magnetometer. There are many varieties, but fluxgate magnetometers have a long heritage in spacecraft applications.

5. Feb 28, 2013

### stavrospao

I know that i must use a magnetometer..but magnetometers measure several indicators(or parameters) of the magnetic field such as H,AE,AU and others..my problem is how can i associate,let's say the H indicator with dBy/dt.thanks anyway

6. Feb 28, 2013

### marcusl

I don't know what AE or AU is. Orient your magnetometer along the direction y. You can approximate the time derivative by taking readings at closely spaced times (separated by intervals of τ) and forming the quantity
$$\frac{\Delta B_y}{\Delta t}=\frac{B_y(t+\tau)-B_y(t)}{\tau}.$$