<p>The beam profile of a radio telescope characterizes its sensitivity to signals as a function of angle off axis.
This is usually divided into a main beam in the target direction and sidelobes in other directions.
As this figure from
<a href="http://iopscience.iop.org/article/10.1088/0067-0049/180/2/246" rel="nofollow noreferrer">Hill et al. 2009</a>
shows, the WMAP main beams and near sidelobes were rather complex:</p>

<p><img src="https://i.sstatic.net/CSWIb.png" alt="WMAP main beams and near sidelobes"></p>

<p><em>Image credit: WMAP Science Team. Each square covers 10x10 degrees.
Top row: beam maps based on multiple observations of Jupiter.
Middle row: beam models fitted to the observed maps.
Bottom row: residual differences between top and middle.
Left and right columns: dishes A and B, which point in different directions.</em></p>

<p>Without further processing, the image of a point source resembles the beam profile.
To reconstruct a clear image, astronomers can
<a href="https://en.wikipedia.org/wiki/Deconvolution" rel="nofollow noreferrer">deconvolve</a>
the observed data with the beam profile.
Lest this operation amplify noise from the observed beam map,
they use a smooth mathematical model of it instead.
The WMAP team developed their beam model using physical optics software called DADRA (Diffraction Analysis of a Dual Reflector Antenna).</p>

<p>The far sidelobes were especially important for WMAP.
The sky has several radio sources, e.g. our galactic center,
much stronger than the desired background signal.
To minimize foreground contamination,
the WMAP team made an all-sky sidelobe map
based on multiple observations of the Moon.
Then they made a mask of the strong sources,
convolved it with the sidelobe map,
and subtracted the result from the observed signal.</p>

<p>For details of how and why they did all that,
see the "Ancillary Data" chapter of the
<a href="https://lambda.gsfc.nasa.gov/product/map/dr5/pub_papers/nineyear/supplement/WMAP_supplement.pdf" rel="nofollow noreferrer">WMAP 9-year Explanatory Supplement</a>
and the
<a href="https://lambda.gsfc.nasa.gov/product/map/dr5/map_bibliography.cfm" rel="nofollow noreferrer">other publications</a>
cited there.</p>

CC BY-SA 3.0
2018-03-25T19:31:54.937Z
2018-03-25T19:31:54.937Z
Mike G
<p>The "beam profile" is what a point source would look like when observed by the instrument.</p>

<p>In general the observed spatial distribution or profile of any source in a WMAP map will be the intrinsic profile or distribution of the source convolved with the beam profile.</p>

<p>In layman's terms it is the amount of smoothing or blurring introduced into the WMAP pictures by limitations of the spatial resolution of the instrument.</p>

CC BY-SA 3.0
2018-03-21T21:49:52.317Z
2018-03-21T21:49:52.317Z
ProfRob
<p>What do people mean by the "beam" profile/model pertaining to
<a href="https://en.wikipedia.org/wiki/Wilkinson_Microwave_Anisotropy_Probe" rel="nofollow noreferrer">WMAP</a>?
Search results are all rather packed with jargon. Is  there a pictorial /layman explanation of it and how does it affect the data? </p>

CC BY-SA 3.0
2018-03-21T14:00:33.360Z
I would echo Kozaky's response that you should cite your sources so we can know for sure what you're talking about. Without context, my guess is that you're talking about the telescope's beam, which is, in the simplest possible terms, the region of the sky capable of being observed. Generally only radio (and microwave) astronomers talk about beams, so your best bet is to find a good intro textbook on radio astronomy. However try looking at [this source](https://www.astron.nl/radio-observatory/observing-capabilities/depth-technical-information/beam-definitions/beam-definitio).
zephyr
CC BY-SA 3.0
2018-03-22T13:49:15.057Z
@Zephyr WMAP is the Wilkinson Microwave Anisotropy Probe, which was an all-sky survey. So your interpretation of  what "beam" means in this case (and others) is incorrect.  The question is not at-all unclear or obscure.
ProfRob
<cosmic-microwave-background><terminology>
WMAP beam profile
Diana
# WMAP beam profile

(Asked by: username_0 on 2018-03-21)

What do people mean by the "beam" profile/model pertaining to
[WMAP](https://en.wikipedia.org/wiki/Wilkinson_Microwave_Anisotropy_Probe)?
Search results are all rather packed with jargon. Is there a pictorial /layman explanation of it and how does it affect the data?

**Tags:** cosmic-microwave-background, terminology
> **Comments:**
> **username_1**: I would echo Kozaky's response that you should cite your sources so we can know for sure what you're talking about. Without context, my guess is that you're talking about the telescope's beam, which is, in the simplest possible terms, the region of the sky capable of being observed. Generally only radio (and microwave) astronomers talk about beams, so your best bet is to find a good intro textbook on radio astronomy. However try looking at [this source](https://www.astron.nl/radio-observatory/observing-capabilities/depth-technical-information/beam-definitions/beam-definitio).  
> **username_2**: @Zephyr WMAP is the Wilkinson Microwave Anisotropy Probe, which was an all-sky survey. So your interpretation of  what "beam" means in this case (and others) is incorrect.  The question is not at-all unclear or obscure.  

---

## 2 answers

### Answer by username_3 on 2018-03-25. Score: 2

The beam profile of a radio telescope characterizes its sensitivity to signals as a function of angle off axis.
This is usually divided into a main beam in the target direction and sidelobes in other directions.
As this figure from
[Hill et al. 2009](http://iopscience.iop.org/article/10.1088/0067-0049/180/2/246)
shows, the WMAP main beams and near sidelobes were rather complex:

![WMAP main beams and near sidelobes](https://i.sstatic.net/CSWIb.png)

*Image credit: WMAP Science Team. Each square covers 10x10 degrees.
Top row: beam maps based on multiple observations of Jupiter.
Middle row: beam models fitted to the observed maps.
Bottom row: residual differences between top and middle.
Left and right columns: dishes A and B, which point in different directions.*

Without further processing, the image of a point source resembles the beam profile.
To reconstruct a clear image, astronomers can
[deconvolve](https://en.wikipedia.org/wiki/Deconvolution)
the observed data with the beam profile.
Lest this operation amplify noise from the observed beam map,
they use a smooth mathematical model of it instead.
The WMAP team developed their beam model using physical optics software called DADRA (Diffraction Analysis of a Dual Reflector Antenna).

The far sidelobes were especially important for WMAP.
The sky has several radio sources, e.g. our galactic center,
much stronger than the desired background signal.
To minimize foreground contamination,
the WMAP team made an all-sky sidelobe map
based on multiple observations of the Moon.
Then they made a mask of the strong sources,
convolved it with the sidelobe map,
and subtracted the result from the observed signal.

For details of how and why they did all that,
see the "Ancillary Data" chapter of the
[WMAP 9-year Explanatory Supplement](https://lambda.gsfc.nasa.gov/product/map/dr5/pub_papers/nineyear/supplement/WMAP_supplement.pdf)
and the
[other publications](https://lambda.gsfc.nasa.gov/product/map/dr5/map_bibliography.cfm)
cited there.


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### Answer by username_2 on 2018-03-21. Score: 0

The "beam profile" is what a point source would look like when observed by the instrument.

In general the observed spatial distribution or profile of any source in a WMAP map will be the intrinsic profile or distribution of the source convolved with the beam profile.

In layman's terms it is the amount of smoothing or blurring introduced into the WMAP pictures by limitations of the spatial resolution of the instrument.


---

