REU Training Solar IrradianceRadiometry Jerry Harder jerry.harderlasp.colorado.edu 303 492 1891 - PowerPoint PPT Presentation

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Title: REU Training Solar IrradianceRadiometry Jerry Harder jerry.harderlasp.colorado.edu 303 492 1891


1
REU TrainingSolar Irradiance/RadiometryJerry
Harderjerry.harder_at_lasp.colorado.edu303 492 1891
2
Things 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
3
Wavelength 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
4
Radiometric Terminology
Advice PAY ATTENTION TO YOUR UNITS!!!
5
Definition 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)

6
The 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

7
Point source illuminating a plane
8
Extended 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

9
Brightness independent of angle for a Lambertian
surface
10
Lambertian source radiating into a hemisphere
P/A is ½ of what you would expect from a point
source
11
History 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

12
Absolute Radiometry
13
Basic process for electrical substitution
radiometry
14
Implementation for SORCE (SIM)
15
Total 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

16
Radiometer Cones
Glory Prototype Cone
Post-Soldered Cone
Glory Prototype Cone Interior
17
TIM 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
18
TSI Record
19
Plancks equation
20
Properties of the Planck distribution
21
Spectral 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

22
SORCE SIM ESR-based spectral radiometry
23
SIM Measures the Full Solar Spectrum
24
Solar 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.

25
SOLSTICE 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

26
SORCE SOLSTICE FUV MUV Spectra
27
The Sun as a blackbody
28
Brightness Temperature
29
Sources of opacity in the solar atmosphere
30
Solar Emissions (VAL, 1992)
31
SIM Time Series at Fixed Wavelengths
32
27 Day Variability Depends on the Formation Region
33
Wavelength Dependence of Sun Images 2
34
Identification 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.

35
Recent quiet and active solar scenes
11 Feb 2006
27 Oct 2004
15 Jan 2005
36
Instantaneous Heating Rates
37
References
  • 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.
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