Can you me with this Hershel telescope beam?

In summary, the resolution of the PACS instrument has been doubled with the use of a faster scan speed. This is due to the smearing of the data that occurs when the instrument is scanning the sky.
  • #1
sonutabitha
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I came to know that the PACS instrument of HERSHEL has a resolution of 5" at a scan speed of 20''/sec whereas it's 10'' at 60''/sec. The resolution has almost doubled with the scan speed. Can you please tell me why it's so?
 
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  • #2
I think the resolution is cut in half with the increased scan speed, not doubled. A resolution of 5" should be twice as good as 10".
 
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  • #3
Drakkith said:
I think the resolution is cut in half with the increased scan speed, not doubled. A resolution of 5" should be twice as good as 10".
Sorry...that's what I meant. The resolution is cut by half for 60''/sec scan speed. Can you please explain why it's so?
 
  • #4
sonutabitha said:
Sorry...that's what I meant. The resolution is cut by half for 60''/sec scan speed. Can you please explain why it's so?

Not sure. I don't know how the telescope works when it is scanning the sky.
 
  • #5
From the PACS observers manual:

"For fast scans in normal and parallel mode, this PSF structure is smeared by detector time constants and data averaging."

http://herschel.esac.esa.int/Docs/PACS/html/ch03.html#sec-characteristics-photometer

See Table 3.1 in that link. Are you referring to the doubling of the FWHM from 5.26 x 5.61 at 10"/s to 5.75 x 9.0 at 60"/s with the Blue detector? If so then that's only along the spacecraft z-direction, which, as the mention above, is due to the increased scan speed. PACS is a bolometer so it doesn't bin photons, it reads a change in temperature due to those photons as a signal instead. When the spacecraft scans faster the thermal properties of the detector mean it can't respond as fast so you smear the temperature-based signal through time, which translates into spatial resolution. Also that signal comes out as a time series, which must be sampled, so I assume that's what they mean when they refer to data averaging.

I don't have a lot of experience directly with Herschel but I've worked with other bolometric imaging systems so this is just my take on their manual.
 
  • #6
The decrease in resolution (softer) is analogous to the effect of lag in old analogue TV cameras. A moving object will be 'smeared out' because of the delay in building up the image on the camera and the rate the object travels across a given spot. The image on the back of the tube is not over the sensor element for long enough to register fully and the charge on the sensor takes time to decay so it leaves behind a trace of the object that passed. A stationary object will give a full resolution image and the resolution will get worse as the speed increases and more picture elements contain traces of the image moving across them.
The acceptable angular speed will be inversely proportional to the decay time of the image on the sensor.
It is due to the Convolution of the time sensitivity function and the time profile of the light (heat) landing on a spot. (Those of a nervous disposition can ignore this bit.)
 

Related to Can you me with this Hershel telescope beam?

1. Can you explain how the Hershel telescope beam works?

The Hershel telescope beam is a type of telescope that uses a large mirror to collect and focus light from distant objects in space. The light is then directed to a detector, which captures and records the image. The telescope beam is able to capture light in a range of wavelengths, including infrared, allowing scientists to study a wide variety of celestial objects.

2. How is the Hershel telescope beam different from other telescopes?

The Hershel telescope beam is unique because it is able to capture light in the infrared spectrum, which is not visible to the human eye. This allows scientists to study objects that emit mostly infrared light, such as cold gas and dust in space. Additionally, the Hershel telescope beam has a much larger mirror than most telescopes, allowing for more precise and detailed images.

3. What kind of research can be done with the Hershel telescope beam?

The Hershel telescope beam is used for a variety of research in the field of astronomy. Some of the key areas of study include the formation of stars and planets, the composition and structure of galaxies, and the search for water and other molecules in space. The telescope has also been used to study comets, asteroids, and other objects in our solar system.

4. How is the Hershel telescope beam operated and controlled?

The Hershel telescope beam is operated and controlled by a team of scientists and engineers on the ground. The telescope is first pointed at a specific target in space using a set of coordinates. Then, the detector captures the incoming light and sends it to a computer, where it is analyzed and processed. The team can then make adjustments to the telescope's position and settings to obtain the best possible image.

5. What have been some of the major discoveries made using the Hershel telescope beam?

Since its launch in 2009, the Hershel telescope beam has made numerous groundbreaking discoveries. Some of the most notable include the detection of water vapor in the atmosphere of a planet outside of our solar system, the discovery of a massive reservoir of water vapor around a distant quasar, and the identification of new molecules in space, such as carbon monoxide and methanol. The telescope has also provided valuable insights into the formation and evolution of galaxies and the role of water in the universe.

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