Interferometric monitor for greenhouse gases (IMG)
Table of contents
- Introduction
- Working principle
- Sensor details
- Applications
- Sources
Physics for sensor technology
Metropolia UAS
Group B
Timo Lummukka, Vadim Amirov, Jaakko Kontkanen, Jaffry Salman
Introduction
Growing awareness on climate change has created an increasing interest to observe concentrations of gases contributing to the warming of the climate. A specially effective way of doing this is to observe this from space, as this enables to an excellent spatial coverage of earth on the flight path of the satellite. Necessary technologies had been unlocked and thus a joint co-operative was launched to create a sensor suitable for the task.
Interferometric monitor for greenhouse gases (IMG) is a satellite born sensor based on FTIR developed in co-operation by JAROS, NASDA and NASA. IMG measured upwelling infrared radiance at fine spectral resolutions. The instrument was designed to have a very high spectral resolution (0.05 cm).The sensor will obtain very accurate spectra of of the thermal infrared radiation from the atmosphere and this data can be used deduce concentrations of greenhouse gases and water vapour.
Working principle
- Interferometry
- Fourier-transform infrared spectroscopy
Interferometry:
Interferometry is a study of wavelenghts, light and interference (Hence the name). The usual component to study is electromagnetic radiation. Waves are superimposed, meaning they are manipulated in a way to give some meaningful analytical results. Usually light is used as the source of the electromagnetic waves.
The basic principle of a Michelson - interferometer: A light is introduced into the system and it is manipulated to travel two different paths. The paths are then guided to meet at a point (The detector). The difference in the path travelled creates an interference pattern and this pattern can be studied and interpreted. This yields e.g. a refractive index which can be purposefully understood.
A schematic of a michelson interferometer
2. http://cnx.org/content/m22326/latest/graphics2.jpg
FTIR: !!JAFFRY CONTINUE HERE!!
Sensor details
The detectors are housed in the IR-detector below the cooling unit. There are three detectors, each corresponding to three different spectral channels.
- Two InSb (Indium Antimony, narrow-gap semiconductor from 3-4 group) detectors for the shorter wavelengths (3.3 - 4.3 nanometers)
- One HgCdTe (Mercury Cadmium Telluride) a semiconductor with a bandgap between 0 and 1.5 eV. This is for the longer wavelengths 4 - 15 nanometer) (4.)
- An onboard blackbody for calibration
- The mirror can also be moved to point toward space for calibration purposes
The sensors are cooled with the cooler to a temperature of below 80 K.
The incoming light beams are splitted into different wavelengths and reflected into the IR-sensor and then the different semiconductors absorb them in their rispectable operating wavelengths. These portions of the reflected beam power electrons to move onto the the next conduction band, thus causing that particular semiconductor to produce a current. This current is then registered and analyzed.
!!ADD THE SENSOR DETAILS!! CAN BE FOUND FROM LINK OF SOURCE 4!!
Detection and monitoring of the vertical and spatial distribution of:
- CO2
- CH4
- O3
- Nitrogen based molecules (N2O, NO2)
- CFC
Applications
IMG has been deployed on atleast two occasions.
- ADEOS 1 (Advanced Earth Observing Satellite): launched in 1996 and flew in the polar orbit.
- ADEOS 2: launched in 2002
Sources
- http://www.sciencedirect.com/science/article/pii/S0273117799009266 (Accessed 15.4.2014)
- http://www.webpages.uidaho.edu/~vonw/pubs/WaldenEtAl_2010.pdf (Accessed 15.4.2014)
- http://suzaku.eorc.jaxa.jp/GLI2/adeos/Project/Img.html (Accessed 15.4.2014)
http://www.sciencedirect.com/science/article/pii/S0273117799009266/pdf?md5=d94773c8e7a93436573522036217bdd1&pid=1-s2.0-S0273117799009266-main.pdf (Accessed 22.2014)