Title: REU Training Solar IrradianceRadiometry Jerry Harder jerry.harderlasp.colorado.edu 303 492 1891
1REU TrainingSolar Irradiance/RadiometryJerry
Harderjerry.harder_at_lasp.colorado.edu303 492 1891
2Things to remember about the Sun
Radius 695,510 km (109 ? radii) Mass 1.989 x
1030 kg (332,946 ?s) Volume 1.412 x 1027 m3
(1.3 million ? s) Density 151,300 kg/m3
(center) 1,409 kg/m3 (mean) Temperature
15,557,000 K (center) 5,780 K
(photosphere) 2 - 3106 K (corona) 1 AU
1.49495108 km TSI (_at_1 AU) 1,361 W/m2
Composition 92.1 hydrogen 7.8 helium
0.1 argon
3Wavelength Dependence of Sun Images
Extreme Ultraviolet Imaging Telescope (EIT) Fe
XII 195 Å
Yohkoh Soft X-ray Telescope (SXT)
Ca II K spectroheliograms NSO Sacramento Peak
He I 10830 Å spectroheliograms NSO Kitt Peak
4Radiometric Terminology
Advice PAY ATTENTION TO YOUR UNITS!!!
5Definition of Solid Angle ( ? )
- ?Solid angle subtended by sphere (from an
interiorpoint) - ?4?
- For an area seen from a point of observation
- Approximation for a distant point (?? small)
6The inverse square law Intensity
- Consider a point source of energy radiating
isotropically - If the emission rate is P watts, it will have a
radiant intensity (J) of - If a surface is S cm from the source and of area
x cm2, the surface subtends x2/S2 steradians. - The irradiance (H) on this surface is the
incident radiant power per unit area
7Point source illuminating a plane
8Extended sources must be treated differently than
point sources
- Radiance (N) power per unit solid angle per unit
area - Has units of W m-2 ster-1
- Lamberts Law J?? Jo cos ?
- Surface that obeys Lamberts is known as a
Lambertian surface
9Brightness independent of angle for a Lambertian
surface
10Lambertian source radiating into a hemisphere
P/A is ½ of what you would expect from a point
source
11History of Absolute Radiometry
- Ferdinand Kurlbaum (1857-1927)
- Radiometric developments for the measurement and
verification of the Stefan-Boltzmann radiation
law.
- Knut Ångström (1857-1910)
- Observations of the Solar Constant and
atmospheric absorption
12Absolute Radiometry
13Basic process for electrical substitution
radiometry
14Implementation for SORCE (SIM)
15Total Irradiance Monitor (TIM)
- Goals
- Measure TSI for gt5 yrs
- Report 4 TSI measurements per day
- Absolute accuracy lt100 ppm (1 s)
- Relative accuracy 10 ppm/yr (1 s)
- Sensitivity 1 ppm (1 s)
- Major Advances
- Phase sensitive detection at the shutter
fundamental frequency eliminates DC calibrations - Nickel-Phosphide (NiP) black absorber provides
high absorptivity and radiation stability
16Radiometer Cones
Glory Prototype Cone
Post-Soldered Cone
Glory Prototype Cone Interior
17TIM Baffle Design
Glint FOV 46.6 degrees
Vacuum Door Base Plate
Shutter
Cone
Precision Aperture
Shutter Housing
Cone Housing
Rear Housing
Baffle 1,2,3
FOV Baffle
18TSI Record
19Plancks equation
20Properties of the Planck distribution
21Spectral Irradiance Monitor SIM
- Measure 2 absolute solar irradiance spectra per
day - Broad spectral coverage
- 200-2400 nm
- High measurement accuracy
- Goal of 0.1 (?1?)
- High measurement precision
- SNR ?500 _at_ 300 nm
- SNR ? 20000 _at_ 800 nm
- High wavelength precision
- 1.3 ?m knowledge in the focal plane
- (or ???? lt 150 ppm)
- In-flight re-calibration
- Prism transmission calibration
- Duty cycling 2 independent spectrometers
22SORCE SIM ESR-based spectral radiometry
23SIM Measures the Full Solar Spectrum
24Solar Stellar Irradiance Comparison Experiment
(SOLSTICE)
Science Objectives
- Measure solar irradiance from 115 to 320 nm with
0.1 nm spectral resolution and 5 or better
accuracy. - Monitor solar irradiance variation with 0.5 per
year accuracy during the SORCE mission. - Establish the ratio of solar irradiance to the
average flux from an ensemble of bright
early-type stars with 0.5 accuracy for future
studies of long-term solar variability.
25SOLSTICE Experiment Concept
- The optical configuration matches illumination
areas on the detector - Interchanging entrance slits and exit slits
provides 2x105 dynamic range - Different stellar/solar integration times provide
103 dynamic range - A optical attenuator (neutral density filter),
which can be measured in flight, provides
additional 102 dynamic range in the MUV
wavelength range for lgt220 nm
26SORCE SOLSTICE FUV MUV Spectra
27The Sun as a blackbody
28Brightness Temperature
29Sources of opacity in the solar atmosphere
30Solar Emissions (VAL, 1992)
31SIM Time Series at Fixed Wavelengths
3227 Day Variability Depends on the Formation Region
33Wavelength Dependence of Sun Images 2
34Identification of solar active regions
- Solar Radiation Physical Model (SRPM) employs
solar images from HAO's PSPT (left panel) to
identify and locate 7 solar activity features
(Rsunspot penumbra Ssunspot umbra P,Hfacula
and plage Factive network E,Cquiet sun) to
produce a mask image of the solar features
(center panel). The SRPM combines solar feature
information with physics-based solar atmospheric
spectral models at high spectral resolution to
compute the emergent intensity spectrum.
35Recent quiet and active solar scenes
11 Feb 2006
27 Oct 2004
15 Jan 2005
36Instantaneous Heating Rates
37References
- Modern Optical Engineering, Warren J. Smith,
McGraw Hill, 1990. - Quantitative Molecular Spectroscopy and Gas
Emissivities, S. S. Penner, Addison-Wesley,
1959. - Statistical Mechanics, J. E. Mayer and M. G.
Mayer, Wiley Sons, 1940. - Absolute Radiometry, F. Hengstberger, Academic
Press, 1989.