INTERFEROMETRY - WHAT HAPPENS IF THE DISHES ARE MOVED CLOSER TOGETHER?
DISH 1 DISH 2
\ /
\ /
\ /
\ /
|<------ BASELINE ---->|
MOVE DISHES CLOSER TOGETHER
===========================
DISH 1 DISH 2
\ /
\ /
|<-- BASELINE -->|
SHORTER BASELINE
|
v
FRINGES BECOME FURTHER APART
|
v
FEWER FRINGES DURING THE SAME TRANSIT
Example:
LONG BASELINE
/\ /\ /\ /\ /\ /\ /\ /\ /\ /\
___/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \___
Many closely-spaced fringes
SHORT BASELINE
/\ /\ /\
_________/ \____________/ \____________/ \________
Fewer, more widely-spaced fringes
Therefore:
DISHES FURTHER APART
=
MORE FRINGES
FRINGES CLOSER TOGETHER
BETTER ANGULAR RESOLUTION
DISHES CLOSER TOGETHER
=
FEWER FRINGES
FRINGES FURTHER APART
LOWER ANGULAR RESOLUTION
Approximately:
Fringe rate proportional to baseline
B
f proportional to ---
lambda
So if you HALVE the distance between the dishes:
10 metres ---> 5 metres
the fringe rate will approximately HALVE
and
the time between fringes will approximately DOUBLE.
At 1420 MHz:
wavelength = approximately 0.211 metres
Approximate angular scale:
lambda
theta ~ ------------
B
For example:
Baseline Angular scale
5 m ~2.4 degrees
10 m ~1.2 degrees
20 m ~0.6 degrees
So, looking at an ezCon interferometry plot:
DISHES FURTHER APART:
/\/\/\/\/\/\/\/\/\/\/\/\/\
DISHES CLOSER TOGETHER:
/\____/\____/\____/\____/\
In simple terms:
MOVE THE DISHES CLOSER
|
v
FRINGES SPREAD OUT
|
v
FEWER FRINGES ON THE ezCon PLOT
By Admin