More about GOES/SEM/XRS
0. Introduction
0.1 Interaction of high-energy photons with matter(atoms)
- Coherent (Thomson and Rayleigh) scattering (< 10 keV)
- Photoelectronic effect (< 100 keV)
- Compton scattering (> 10 keV)
- Electton-Positron pair production (> 1.022 MeV)
- Photodisintegration (> 10 MeV)
[GOES/SEM/XRS] observing range :
1 - 8 Å (softer channel, long channel)
0.5 - 4 Å (harder channel, short channel)
[eV]·[nm]=1240
[keV]·[Å]=12.4
∴ 1 - 10 (Å) ↔ 1.24 - 12.4 (keV),
0.2 Photoelectronic effect detectors
- Ionization chamber : collects all the charges created by direct
ionization through the application of an electric field
(e.g., GOES/SEM/XRS).
- Proportional counter : a detector output is proportional to the
radiation energy by the gas multiplication mechanisms
(e.g., Yohkoh/WBS/SXS).
- Geiger counter : cheap, robust, but has dead time. no energy resolution.
- Scintillation counter : measures photons produced by scintillation
(e.g., Yohkoh/WBS/HXS [NaI] & GRS [BiGeO])
- Photomultiplier : photoelectrons are multiplied while passing several
dynodes.
- Microchannel plate : a bundle of photomultiplier tubes
(e.g., ROSAT/HRI & WFC, SOHO/UVCS & SUMER).
- Micro calorimeter : measures temperature rise due to incident photons
(e.g., Hitomi/SXS: Soft X-ray Spectrometer).
- Semiconductor detector: measures current produced by electron-hole pairs
(e.g., Ge detector).
- Photodiode : a kind of semiconductor detector using diode to collect
current.
- Charge Coupled Device: an array of photodiodes
(Yohkoh/SXT is the first astronomical satellite observing with CCD).
1. GOES/SEM/XRS
GOES Spacecraft generation
- 1st generation : GOES 1-7 (A-H, FYI, G: launch failure)
- 2nd generation : GOES 8-15 (I-P)
- 3-axis stabilized.
- 8-12 (I-M) built by Space Systems Loral (SS/L)
- 13-15 (NOP) built by Boeing Satellite Systems (BSS)
- 3rd generation : GOES 16
(R. FYI, Q: cancelled in 2004)
- XRS uses photodiode, instead of ionization chamber.
- being built by Lockheed Martin.
GOES instruments (NOP series)
XRS/EUV assembly
XRS design
(from Hanser and Sellers, 1996, SPIE vol. 2812, p.344).
Spectral responses
Ion chamber theoretical responses
(from Garcia, H., Solar Physics vol.154, p.275-308)
GOES/XRS spectral responses
(from Machol and Viereck, 2015, "GOES_XRS_readme.pdf" at NGDC web site)
Data calibration
- During the 1st generation, GOES/XRS observed the flux modulated
by satellite's rotation ("pulses" of flux. the bottom value of the pulse
are used as background removal).
- After the second generations, this method is no more available.
- Absolute calibration: prelaunch lab-experiment using Fe55 emission
(FYI, Fe55 --> Mg55 through the process of K-shell electron capture,
followed by the emission of X-rays corresponding to L to K transitions.
the photon energy is ~5.9 keV, half time is 2.7 years).
- Now using CHANTI solar spectral model.
