Table of Contents
UFYS2010 Radio Astronomy Instrumentation and Interferometry 6 op
Lectures (24 h)
Thu 10-Jan-2013 - 25-Apr-2013 weekly at 14.15-16.00, Qh314
Exercises
Thursdays (TBA) at 16.00-17.00, Qh314
Exam
Wed 15.5 12 - 15 and
Fri 31.5 14 - 17
in Qh314
Lecture 31.1.2013 was cancelled
The lecture was cancelled as we had problems transporting a 600 kg 1930's lathe that was donated to Tuorla. It was once used by Prof. Yrjö Väisälä, the founder of Observatory, also during the war, a very historical piece of equipment. All did not go well (…) but fortunately there were no injuries (talk about a close shave…)
Let's have a double lecture next time (7.2.2013), antennas and receivers.
Demos
Let's postpone the deadline until 21.3 and 4.4…!
Comments
Sky noise temperature
If $T_{sky}$ is not given and you cannot calculate it, assume it is zero (it is always $< T^{phys}_{atm}$).
Surface errors
The equation of efficiency reduction due to surface errors is in Lecture 3, slide 20:
$\eta_{\rm{sf}} = e^{-({4\pi\sigma/ \lambda})^2}$
e.g. for surface error $\sigma = \lambda/16$, the efficiency factor is $\eta_{\rm{sf}} \simeq 0.5$.
Radiometer balancing
Switching radiometers compare a stable reference noise source to the one that is been measured. This way one can compensate gain (amplification constant) variations in the radiometer (mainly amplifiers). In order this to be successful, the reference noise should be at the same level as the one that is measured, i.e. the radiometer should be balanced.
As an analogy, consider a case where you have a pile of sticks and you have to measure if they are of the same length. The task is easy if your reference is about the same length as the sticks to be measured… If the length differs considerably, the measuring accuracy is reduced.
Decibels
Decibel is a 10-based logarithmic measure of power ratios1), somewhat like magnitude: $\rm{dB} = 10\cdot\log_{10}(\rm{r})$, e.g. if something is two times larger, it can be said that it is 3 dB larger. It is just a way to express ratios conveniently. Most of the equations use normal ratios, so you have to convert decibels to ratios. E.g. if a gain of an amplifier is 30 dB, you should use 1000 in equations. Decibel is unitless, it is only a number.
Lecture material
Demo results
| Number | Problems | Points |
|---|---|---|
| 504508 | 12345 | 5 |
| 504485 | 12345 | 5 |
| 504500 | 12345 | 5 |
| 506628 | 12345 | 5 |
| 74956 | 12345 | 5 |
| 72076 | 0 | |
| 506629 | 12345 | 5 |
| 506550 | 0 | |
| 504471 | 12345 | 5 |
| 72999 | 1245 | 4 |
| 78446 | 0 | |
| 505957 | 12345 | 5 |
| 15324 | 1245 | 4 |
Interferometry lecture notes
Much of the interferometry basics-related lectures are based on NRAO's excellent lecture series:
http://www.cv.nrao.edu/course/astr534/Interferometers1.html
http://www.cv.nrao.edu/course/astr534/Interferometers2.html
The main page is in
http://www.cv.nrao.edu/course/astr534/ERA.shtml
PDF's can be found here:
http://www.cv.nrao.edu/course/astr534/PDFnew.shtml
A good review of interferometric imaging (more detailed than necessary for this course):
http://hesperia.gsfc.nasa.gov/summerschool/lectures/bastian/Notes_on_Synth_Img.pdf
Here are some links and notes about *difmap* data reduction software: difmap
