The temperature of the atmosphere can be measured by infrared radiation using a satellites At some infrared wavelength the atmospere is transparent, but at other wavelength radiation is absorbed and emitted by molecules of gases. By measuring the infrared radiation at different wavelengths, the satellite can see radiation emitted from different areas. The brightness of the radiation varies with temperatures.
Using Thermographic camera on human or object
IR camera are use to detect temperature of object the radiation are detect by a ccd then amplify the signal by an amplifier then show in CRT images in different brightness signal. There is an equation to caculate the energy of radiation on our skin which is Stefan’s Law.
Here is a basic circuit of an thermographic camera:
Fig 5
What is Black body?
I had mention black body in the previous paragraph and now I am going to explain it. Black body is an object that absorbs all , no radiation will be , and all radiation will be absorbed. The amount and type of electromagnetic radiation they emit is directly proportional to their absolute temperature on the surface. When the temperature increases, the wavelengths of the radiation emitted become shorter, if the object is so hot that it can emit visible light.
How is Radiation Absorbed?
Heat cause the molecules and atoms to vibrate, From the experiments of Hertz and Maxwell's predictions that oscillating charges emitted electromagnetic radiation It was known from Maxwell's equations that this radiation traveled at the speed of light when a object was heated, the vibrations on a molecular and atomic scale included some oscillating charges. then these oscillating charges would radiate, by giving off heat or light.
Different materials have different response to radiation. For a shiny metallic surface, the light isn't absorbed it gets reflected because a piece of metal has free electrons. This is why metals can conduct electricity. It is also why they are shiny. These free electrons oscillate together when light wave shine on it. Then radiate electromagnetically, this radiation from the oscillating electrons is the reflected light. In this situation, little of the incoming radiant energy is absorbed, it is just reradiated means it is reflected.
For a black material like soot, light and heat are completely absorbed, and the material gets warm. Electromagnetic wave charges in the material causing the atom to oscillate and absorb energy from the radiation. Soot can also conduct electricity but not as well as metal. There are unattached electrons, which can move through the whole solid. When they get heat up which cause vibration, so they transfer the kinetic energy into heat. They move very freely so they can accelerate and gain energy from the electric field in the light wave. They transfer energy from the light wave into heat. Fig 6, 7 soot
BLACK BODY RADIATION CURVES( fig 8)
The black body radiation curve (Fig8) shows that the black body radiates energy at every wavelength. The curve gets infinite and very close to the x-axis. The curve has a infinite x value(wavelength). In the graph the peak shows that the black body emits most of the radiation at a particular temperature wavelength.
This graph Fig 9 shows how the black body
radiation curves change in various temperatures. It shows temperature and power radiated has a direct proportional relationship. The area between the curve and the wavelength axis equal the power radiate from unit area of the surface over the wavelength range. The area increase is proportional to T4 In Stefan’s law.
Planck Radiation Formula Times (The average energy per radiation energy in frequency or wavelength)
This formula can use to predict the spectral intensity of at all wavelengths that emmit from a at different level of temperature. It is using the same theory of phanck’s law, but more compilcated by using the frequency or wavelength of a radiation times the times the Bose-Einstein distribution function.
Explain Einstein-Bose distribution function
Fig10
The distribution function is the probability that a particle is in energy state E. The create the ideas of to the case where energy level of the particle are randomly.
- At thermal equilibrium, the distribution of particles among the available energy states will take the most probable distribution consistent with the total available energy and total number of particles.
- Every specific state of the system has equal probability.
- There is no restriction on the number of particles which can occupy a given state. (fig10)
These three rules suggest every particle have probability to gain or lose energy, in different state like gas, liquid and solid. The probability also depends on the amount of particles. That’s why to calculate the average radiation energy need to time the Einstein-Bose distribution function.
Types of detectors in infrared camera
A radiation detector is a device that produces an output signal, which depends on the amount of radiation hitting to the detector, thermographic camera’s detector are divide into two types: cooled infrared detectors(photon) and uncooled infrared(thermal)
Uncooled infrared detectors
uncooled thermal cameras use a sensor operating at a variable temperature. Modern uncooled detectors convert incident radiation into heat, by raising the temperature of the detector element. This change in temperature is converted to an electrical signal. It is also can be respond to a wide range of wavelengths. Uncooled infrared detectors display high sensitivity at room temperature. Uncooled infrared detector don’t need to be frozen so makes the infrared camera a smaller size and cheaper, however the image quality and sensitivity are lower then cooled detectors.
Cooled infrared detectors
Cooled detectors are mainly use in astronomy it store in a vacuum case and cooled. This will increase the because the dector’s temperatures are lower than the objects we want to detect . (typical cooling temperatures range from 4 to 110 K, 80 K.)Without cooling, the sensors will become less sensitive and can’t detect some radiation. The camera need a few minutes to cool down before it use. Cooled infrared cameras provide better image quality compared to uncooled ones.that’s why it is use in telescope. It is a photon type detectors such as photovoltaic or photoconductive sensors operate by photon interaction. They provide high sensitivity and response speed. However, photon detectors require high cost cryogenic operation to minimize the noise sources to obtain the high sensitivity.
Materials used for infrared detection are liquid-helium cooled silicon bolometers, and a wide range of semiconductor device.(fig11)
Near, Mid and Far Infrared In astronomy
By using different wave length of infrared can collect different information from the space, because Infrared radiation is emit by any object that has a temperature the only difference is the intensity. Normally long wavelength infrared would able to collect low temperature stars. Some infrared wavelengths are better to use for studying certain stars depend on the temperature of the star.
Visible near-infrared mid-infrared
fig12
When we use near-infrared to capture a image, large red giant stars and low mass red dwarfs can see clearly in the near infrared image. The dust appears transparent to near infrared. The cooler stars or objects can be detect by longer wave length infrared (mid and far infrared) The cooler star means the star with lower temperature, this is because longer wavelength of infrared could sense low temperature.
Fig 13 Visible View of the M81 galaxy Fig 14 Near-Infrared View of the M81 galaxy
Near infrared
In the images above shows the center part of a galaxy, which is cover by thick area of dust in visible light image, by using the near-infrared it becomes transparent. The near-infrared image can detect and show cool reddish stars which can not detect by the visible light. These stars are mainly red dwarfs and red giants.
“Red giants are large reddish or orange stars which are running out of their nuclear fuel. They can swell up to 100 times their original size and have temperatures which range from 2000 to 3500 K. Red giants radiate most intensely in the near-infrared region.Red dwarfs has a temperature of about 3000 K”
This show shorter wavelength is use to detect star or object that with a hight temperature and longer wave length is use to detect cooler stars
Further information of infrared in astronimy Fig 20
Now I will introduce the satellite which use infrared camera to collect information from the space it’s call AKARI (fig 20). AKARI is also call IRIS (Infrared Imaging Surveyor) it is the second space mission for infrared astronomy in Japan. Another satellite is call IRAS (Infrared Astronomical Satellite)launched in 1983 by the United Kingdom, American and Netherlands. This AKARI mission is a plan to investigate the astronomy with much better sensitivity, resolution image and wider wavelength. AKARI has a 68.5cm telescope which was cooled down to 6K, and will observe in the wavelength range from 1.7 (near-infrared) to 180 (far-infrared) micron. “AKARI has been placed in a sun-synchronous polar orbit of about 700 km.” Because the AKARI satellite has higher sensitivity and better resolution in the camera compare to the IRAS satellite so more star may discover by it and more reliable information can be collect. Here are the targets which will be investigated by AKARI.
“To understanding the formation and evolution of galaxies”,
“To inquire into the formation process of stars and planetary systems”
Inside the satlelite
The most important part of AKARI is the FIS (Far-Infrared Surveyor) for far-infrared observations and the IRC (InfraRed Camera) for near and mid-infrared observations.
FIS (Far-Infrared Surveyor) Fig 21
The FIS is the main part to make an sky survey at far-infrared wavelengths. Two detectors of the FIS are photoconductors which use semiconductor crystal Ge:Ga, Germanium doped with Gallium. Stressed Ge:Ga chips are sensitive to far-infrared light of longer wavelength than without stress. Each detector is used with filters. The FIS is also used to detect faint objects or to perform spectroscopy using a Fourier transform spectrometer.
IRC : InfraRed Camera Fig 22
The IRC is from by three independent camera systems. The NIR camera is sensitive to near-infrared wavelengths in the 1.7 - 5.5 micron range. The MIR-S camera is assigned to shorter mid-infrared wavelengths over the 5.8 - 14.1 micron range and the MIR-L camera is assigned to longer mid-infrared wavelengths of 12.4 - 26.5 micron.
One of the advantages of the IRC is that it can observe many information at a time because of large detector arrays (512x412 for NIR, 256x256 for MIR). Each camera can select an specific waveband to observe by using filters. IRC is equiped with prisms and grisms so it can perform efficiently in the observation. Table of data fig 23
Other part in the satellite Fig 24 design plan of the satellite
ASTRO-F satellite contain a cryostat and a bus module. A telescope and other instruments are stored in the cryostat and cooled by liquid Helium. The bus module is use to control the satellite, handling data, and communication with the ground system of the satellite. The height and weight of the satellite are 3.7 meters and 952 kg. The cryostat and the bus module have independent structures so reduce the heat warm up the cryostat
Cryostat Fig 25 (design plan of Cryostat)
170 liter of superfluid liquid Helium is contain in the tank of the cryostat and cools the instruments and the telescope down to a very low temperature.
Two sets of Stirling-cycle mechanical coolers are attatch to the liquid Helium. The use of the mechanical coolers is to extends the Helium life and reduce the quantity of Helium to be carry into space. AKARI will make observations for one and a half years keeping a very low temperature using both liquid Helium and the mechanical coolers.
Telescope Fig 26
The AKARI telescope has a focal length is 4200 mm and effective aperture is 68.5 cm. The entire telescope is cooled down to about 6K during observations. The aim of the cooled telescope is to suppress harmful thermal radiation radiated from telescope itself. The telescope was made of a primary mirror, a secondary mirror, which support the secondary mirror, and baffles which prevent stray light. The trusses are made of Beryllium (Be) metal. Beryllium is a material with light weight and good thermal conduction.
The primary mirror Fig 27
The primary mirror is made of Silicon Carbide, a lightweight and rigid material. The back side of the mirror is hollow out in order to make it lighter. The actual weight of the 71 cm (effective diameter is 67 cm) primary mirror is only 11 kg. The surface of the primary mirror is coated by Gold to increase the reflectance at infrared wavelength.
Summary
Infrared is an electromagnetic radiation it has wide range of application in different way. The infrared radiation are very important in exploring astronomy because of star and other type of comet give out radiate heat energy so by using different wavelength infrared could detect different type of star depends on the heat they radiates. It also has the potential to detect a lot of unknown comets. In the Japanese project the satellite is expected to detect more than 50 new comets.
Bibliography
(What is infrared)
Royal institution magnetic researches friction infrared by Tyndall John p.30 to 32
These resources had give me a basic idea of what infrared is and how is discover by with experiment specially from the book it had a detail information of the experiment. Also, the wide range application of infrared in different area.
(Type of infrared)
These have great explanation and information on three types of infrared. It helps to understand different wavelength of infrared has different specific uses. It help further in the astronomy part which need to explain different wavelength observes different type of star and comet.
(Application)
Forcasting the weather satellites page 3
These information give me specific information of individuals application like how satellite sense the temperature and give a basic understanding of how infrared camera work, this help me get interest and had a much more detail on how the camera and detector work.
(Inside the camera)
These web site had helped me to explore the structure of the detector in the camera and different between two types of detector, cooled and uncooled. Also how the detector change information to current. I also find and equation which could calculate the intensity of infrared on object surface.
(black body)
http://www.egglescliffe.org.uk/physics/astronomy/astonomy.html
Physics A to Z page
These are one of the important I found, infrared radiation emit by star in space and use infrared camera to sense heat are basically because of the black body theory and without these information the explanation will not be clear. They also helped me to understand the relationship in electromagnetic waves. I also linked to the plank’s radiation formula and Einstein-Bose distribution function to introduce how amount of radiation can be calculate
(astronomy) http://galileo.phys.virginia.edu/classes/252/black_body_radiation.htm
These information help me to found pictures of star, galaxy and comet. Also help me to understand how useful infrared is in the astronomy by discover new star and information before star form. On the other it also help me to define different type of infrared to use in sensing different properties satrs
(AKARI satellite)
These information had help me to write the further information of infrared use in astronomy it is one of the biggest mission in the 21 century it has many task to complete in the space also helped me to understand different part of the satellite and the basic structure of it also the type of sensor it uses.
Sources of diagram and graphs
Fig 1
Fig2 http:// ipac.caltech.edu/cosmic_classroom/cosmic_reference/emspec.html
Fig3
Fig4
Fig5 physics today p.23
Fig6
Fig7
Fig8 and 9
Fig10
Fig 11
Fig 12
Fig 13
Fig 14-20
Fig 21-27
Content page
Introduction
What is infrared?
electromagnetic spectrum relate to energy
Type of infrared
Application
Thermographic camera expaination
Inside the camera Using Thermographic camera on human or object What is Black body? Planck Radiation Formula Types of detectors in infrared camera
Infrared in astronomy
Further information of infrared in astronomy AKARI satellite Inside the satlelite (structure)
Summary
Bibliography
