1. Solar Spectral Irradiance Measurements by LASP
Frank Eparvier
University of Colorado
Laboratory for Atmsopheric & Space Physics

2. LASP’s Irradiance History
Spectral Region
Wavelength (nm)
Missions
Soft X-ray (XUV)
SNOE, SORCE, TIMED, SDO
Extreme Ultraviolet (EUV)
30-115
TIMED, SDO
Far Ultraviolet (FUV)
SME, UARS, TIMED, SORCE
Middle Ultraviolet (MUV)
SME, UARS, SORCE
Near Ultraviolet (NUV)
UARS, SORCE
Visible (VIS)
SORCE
Near Infrared (NIR)
Total Solar Irradiance (TSI)
all
SORCE, Glory
Green indicates missions in development

3. Irradiance Calibration Essentials
Understand the Measurement Equation:
Know all the parameters that go into the measurement to irradiance conversion and assess how to best quantify each
Do a thorough error analysis and uncertainty budget
Calibrate pre-flight:
Use a standard radiometric EUV source
Primary standards, such as NIST SURF-III source, are preferred (note: SURF beam flux known to <1% for EUV ranges)
Track in-flight:
Any instrument changes that will affect results
E.g. detector flat fields, gain changes, temperature effects, background signals, FOV maps, alignment changes…
Re-Calibrate in-flight:
As close after launch as possible (changes since pre-flight calib.)
On a regular basis thereafter in order to track absolute changes
E.g. redundant channels, on-board sources, rocket underflights, stellar comparisons
Validate:
With measurements made with other (preferrably independent) instrumentation
Comparisons with models

4. TIMED Mission Ionosphere Mesosphere Thermosphere
Energetics
Dynamics
TIMED primary science goals are to understand :
energy transfer into and out of the Mesosphere and Lower Thermosphere/Ionosphere (MLTI) region of the Earth's atmosphere, and
basic structure (i.e., pressure, temperature, and winds) of the MLTI region.
TIMED launched on Dec. 7, 2001
Normal operations began on Jan. 22, 2002, extended through 2010

5. Solar EUV Experiment (SEE) Objectives
Study the solar radiation input to the mesosphere, lower thermosphere, and ionosphere (MLTI)
Accurately determine the solar vacuum ultraviolet (VUV: below 200 nm) irradiance
Study the impact of solar changes on Earth’s upper atmosphere utilizing atmospheric models
Improve the understanding of solar VUV variability
Identify and quantify the sources of solar VUV variability
Develop better proxy models of the solar VUV irradiance

6. EGS = EUV Grating Spectrograph
SEE Instrumentation
XUV
EUV
FUV
EGS nm with Dl=0.4 nm
XPS nm with Dl=7-10 nm
and Ly-a (121.6 nm) with Dl=2 nm
TIMED spacecraft was launched on 7 December 2001, and its mission has been extended through 2010.
EGS = EUV Grating Spectrograph
Rowland-circle grating spectrograph with 64x1024 CODACON (MCP-based) detector
XPS = XUV Photometer System
Set of 12 Si photodiodes - 8 for XUV, 1 for Ly-a, and 3 for window calibrations
Cadence = 10-sec integrations for 3 minutes of every 96 minute orbit

7. SEE EUV Grating Spectrograph (EGS)
Normal Incidence, 1/4 m Rowland Circle Spectrograph
nm range
Dl = 0.4 nm
(0.167 nm/pixel)
Redundant channel used weekly for tracking degradation
EUV
FUV
Example EGS
Measurement
Lyman-a Filter
Flat Field
(Hg) Lamp
Detector
HVPS
Optical Cube
Solar Aspect Sensor
(SAS)
Slit
Selector
Vacuum
Door
64 x 1024
CODACON
Charge
Amp

8. SEE XUV Photometer System
XUV Photometer System (XPS)
8 XUV Si photodiodes nm
Dl ~ 7 nm
1 Lyman-a (121.6 nm) photometer
3 bare (Vis) Si photodiodes
measure FS filter transmission
8 position filter wheel
1 clear aperture per diode
2 fused silica filters per diode
5 blank apertures per diode
Example XPS Measurement
Filter
Wheel
(inside
purge
cover)
Photodiode
Electronics
Section
Control

9. SEE XPS Bandpasses + Ly- channel
= channels used exclusively since July 2002 filter wheel anomaly

10. SEE Rocket Underflights
SEE satellite instruments are calibrated regularly with sounding rocket underflights of prototype SEE instruments (XPS and EGS).
Rocket instruments calibrated at NIST-SURF pre and post flight, to transfer calibration to SEE instruments.
SEE underflights:
08-Feb-2002
12-Aug-2003
15-Oct-2004
24-Oct-2006 (will fly XPS and rocket version of EVE)

11. Rocket XPS Bandpasses + Ly- channel
+ For Oct rocket flight, Be filter channels added to reproduce GOES XRS bandpasses

12. Solar Radiation and Climate Experiment (SORCE)
SORCE Mission
Solar Radiation and Climate Experiment (SORCE)
PI: Tom Woods (Gary Rottman retired in 2005)
Co-I’s: Jerry Harder, George Lawrence, Bill McClintock, Greg Kopp, Erik Richard, Marty Snow, and a bunch of others
SORCE was launched on 25 January 2003, and its mission is through 2008.

13. Solar Irradiance Modeling
SORCE Objectives
Make daily measurements of total solar irradiance (TSI) with an absolute accuracy of 0.01% and with a long-term relative accuracy of 0.001% per year.
Make daily measurements of the solar ultraviolet irradiance, 120 to 300 nm, with a spectral resolution of 1 nm, with an absolute accuracy of 5%, and with a long-term relative accuracy of 0.5% per year.
Make daily measurements of the solar irradiance between 300 and 2000 nm with a spectral resolution (Dl/l) of at least 1/30, with an absolute accuracy of 0.05%, and with a long-term relative accuracy of 0.01% per year.
Improve our understanding of how and why the variability occurs at the Sun and how the variable irradiance affects our atmosphere and climate. To use this knowledge to estimate past and future solar behavior and climate response.
Total Irradiance
Monitor (TIM)
SOLSTICE
Spectral Irradiance
Monitor (SIM)
Solar Irradiance Modeling
Atmospheric Modeling

14. SORCE Measures TSI and SSI
Instrument
 Range (nm)
(nm)
TIM: Total Irradiance Monitor
TSI (all) -
SIM: Spectral Irradiance Monitor
1-30
SOLSTICE: Solar Stellar Irradiance Comparison Experiment
0.1
XPS: XUV Photometer System
0.1-27, 121.6
7-10

15. SORCE Total Irradiance Monitor (TIM)
Instrument Type: Cavity Bolometer
Wavelength Range: All
Wavelength Resolution: N/A
Optics: None
Detector: Conical Electrical Substitution Radiometer (ESR)
Absolute Accuracy: 0.01% (100 ppm)
Long-term Accuracy: 0.001% (10 ppm)
Field of View: 4° cone
Mass: 7 kg
Orbit Average Power: 14 W
Orbit Average Data Rate: 1.6 kbits/s
Redundancy: 4 ESRs (2 pairs)
Heritage: New design
Pre-flight Cal. Std: NIST Volt and Ohm
In-flight Cal.: Redundant channels, Shuttle underflight

16. SORCE SOLAR STellar Irradiance Comparison Experiment (SOLSTICE)
Instrument Type: Grating Spectrometer
Wavelength Range: nm
Wavelength Resolution: nm
Optics: Mirrors, Grating, ND Filters
Detector: Photomultiplier Tube (PMT)
Absolute Accuracy: 5%
Long-term Accuracy: 0.5%
Field of View: 1.5° x 1.5°
Mass: 36 kg (2 channels)
Orbit Average Power: 33 W (2 channels)
Orbit Average Data Rate: 0.8 kbits/s (2 ch)
Redundancy: Dual channels, dual PMTs
Heritage: UARS SOLSTICE
Pre-flight Cal. Std: NIST SURF-III
In-flight Cal.: Bright early-type stars, Redundant channels

17. SORCE Spectral Irradiance Monitor (SIM)
Instrument Type: Prism Spectrometer
Wavelength Range: ,000 nm
Wavelength Resolution: nm
Optics: Prism
Detector: ESR, Si photodiodes, and InGeAs photodiodes
Absolute Accuracy: 0.03% (300 ppm)
Long-term Accuracy: 0.006% (60 ppm)
Field of View: 1.5° x 1.5°
Mass: 18 kg
Orbit Average Power: 42 W
Orbit Average Data Rate: 2.0 kbits/s
Redundancy: Dual channels
Heritage: New design
Pre-flight Cal. Std: Trap diode-NIST ESR
In-flight Cal.: Redundant channels, Prism transmission

18. SORCE XUV Photometer System (XPS)
Instrument Type: Filter Photometer
Wavelength Range: 1-35 nm
Wavelength Resolution: 5-10 nm
Optics: Thin film filters (deposited on Si diodes)
Detector: 12 Si photodiodes: 8 XUV, Ly-a, 3 bare
Absolute Accuracy: 20%
Long-term Accuracy: 4%
Field of View: 4° cone
Mass: 3 kg
Orbit Average Power: 9 W
Orbit Average Data Rate: 0.3 kbits/s
Redundancy: 3 redundant XUV diodes
Heritage: TIMED SEE, SNOE, rocket XPS
Pre-flight Cal. Std: NIST SURF-III Ref. Si Diode
In-flight Cal.: Redundant channels

19. SORCE XPS Bandpasses + Ly- channel
= channels used routinely since Dec 2005 filter wheel anomaly
(other channels used once monthly)

20. SDO Misson http://sdo.gsfc.nasa.gov/
SDO is the First Space Weather Research Network Mission in the LWS Program
SDO Mission Science Objectives
The primary goal of the SDO mission is to understand, driving towards a predictive capability, the solar variations that influence life on Earth and humanity’s technological systems by determining:
How the Sun’s magnetic field is generated and structured
How this stored magnetic energy is converted and released into the heliosphere and geospace in the form of solar wind, energetic particles, and variations in the solar irradiance.
SDO Science Investigations
EUV Variability Experiment (EVE)
PI: Tom Woods, University of Colorado Measures the solar extreme ultraviolet (EUV) spectral irradiance to understand variations on the timescales which influence Earth’s climate and near-Earth space
Helioseismic and Magnetic Imager (HMI)
PI: Phil Scherrer, Stanford University Images the Sun’s helioseismic, longitudinal and vector magnetic fields to understand the Sun’s interior and magnetic activity
Atmospheric Imaging Assembly (AIA)
PI: Alan Title, LMSAL Provides multiple simultaneous high-resolution images of the corona over a wide range of temperatures to determine magnetic structure and variability
Mission Specs:
August 2008 launch
Inclined Geosynchronous Orbit
Five-year mission baseline
3-axis stabilized spacecraft
Continuous solar pointing
Data transmission: continuous high rate data stream ~150 Mbps compressed data at Ka-Band
Mission development and management at GSFC
Project Scientist Dean Pesnell

21. The EUV Variability Experiment (EVE)
Principal Investigator:
Tom Woods (Univ. Colorado - LASP)
Co-Investigators:
Univ. Colorado - LASP: Frank Eparvier, Gary Rottman
Univ. Southern Calif.: Darrell Judge, Andrew Jones
Naval Research Lab: Judith Lean, John Mariksa,
Harry Warren, Don McMullin
MIT-LL: Greg Berthiaume
Univ. Alaska - GI: Scott Bailey
Collaborators:
NOAA - SEC: Tim Fuller-Rowell, Rodney Viereck
Utah State Univ.: Jan Sojka
Space Environ. Tech.: Kent Tobiska
EVE Science Goal:
Specify and understand the highly variable solar extreme ultraviolet (EUV) electromagnetic radiation and its impacts on the geospace environment and the societal consequences
EVE Science Objectives:
Specify Irradiance: Specify the solar EUV irradiance and its variability on multiple time scales (seconds to years).
Understand Variability: Advance current understanding of how and why the solar EUV spectral irradiance varies.
Nowcast/Forecast: Improve the capability to predict (nowcast and forecast) the EUV spectral irradiance variability.
Geospace Impacts: Understand the response of the geospace environment to variations in the solar EUV spectral irradiance and the impact on human endeavors.

22. EUV Variability Experiment (EVE)
EVE purpose:
To measure and model the solar EUV irradiance variations due
to flares (seconds), solar rotation (days), and solar cycle (years)
ESP
MEGS B/P
MEGS A
SAM
EOP
EEB
The Key Components of EVE
EVE Optical Package (EOP)
Multiple EUV Grating Spectrograph (MEGS)
MEGS A + SAM (Solar Aspect Monitor)
MEGS B + P (Photometer Channel)
EUV Spectrophotometer (ESP)
EVE Electrical Box (EEB)
EVE processor
CCD power converter/regulator
ESP power converters
EVE Metrics
Power
Average (28V) watts
Mass
54.2 kg
Data Rate
2 Kbps (engineering)
7 Mbps (science)
Wave Length Range
0.1 nm – 105 nm
Dimensions (EVE Envelope)
~39”L x 24”W x14”H

23. How does EVE measure the EUV?
Multiple EUV Grating Spectrograph (MEGS)
At 0.1 nm resolution
MEGS-A: 5-37 nm
MEGS-B: nm
At 1 nm resolution
MEGS-SAM: 0-7 nm
At 10 nm resolution
122 nm
Ly-a Proxy for other H I emissions at nm and He I emissions at nm
EUV Spectrophotometer (ESP)
At 4 nm resolution
17.5, 25.6, 30.4, 36 nm
At 7 nm resolution
0-7 nm (zeroth order)
In-flight calibrations from ESP and MEGS-P on daily basis and also annual calibration rocket flights Dl
0.1 1 4 7 10 nm

24. EVE Calibration Rocket(s)
Like TIMED-SEE, SDO-EVE will have periodic sounding rocket underflights to transfer calibration from NIST-SURF to satellite instruments.
1st flight of EVE rocket instruments planned for 24-Oct-2006
After SDO launch plan L+2 months, L+8 months, then increasing times after that for a total of 5 rockets for the 5 year SDO mission.
Rocket Payload:
MEGS (A, B, P, and SAM)
ESP
XPS
CLASSIC (Ly-a imager)
AXIS (0-5 nm avalanch photodiode)

25. Examples of Solar Variations
Solar Cycle (11-years)
Solar Cycle - months to years
Evolution of solar dynamo with 22-year magnetic cycle, 11-year intensity (sunspot) cycle
Long-term H I Lyman-a time series has been extended with TIMED SEE measurements
SORCE and TIMED SEE are providing new information on solar irradiance variability
Solar Rotation (27-days)
XUV 0-7 nm
H I nm
Solar Rotation - days to months
Beacon effect of active regions rotating with the Sun (27-days)
Flares
Flares - seconds to hours
Related to solar storms (such as CMEs) due to the interaction of magnetic fields on Sun

26. New Results for Solar EUV Variability
TIMED SEE provides new, more accurate results of the solar EUV variability since the AE measurements in 1970s (Woods et al., JGR, 2005).
Example variability for the 4 components of the Flare Irradiance Spectral Model (FISM) by Phil Chamberlin (CU PhD dissertation, 2005).
TIMED SEE, SORCE, and UARS used to develop new proxy models of the solar UV irradiance (0-200 nm).
UARS = UARS SOLSTICE solar cycle results
[Woods and Rottman, 2002]

27. Flare Irradiance Spectral Model (FISM)
Developed by Phil Chamberlin (defended PhD 2005)
Based on lots of data:
Daily Average Data Sets:
nm: SEE Level 3 (Combination of SEE and SORCE XPS)
nm: SEE Level 3 (2002-Present)
nm: UARS SOLSTICE ( )
Flare Impulsive Phase Data Sets:
0-27 nm: SORCE XPS (2003-Present)
nm: SEE Level 1
Flare Gradual Phase Data Sets:
0-190 nm: SEE Level 3A
FISM is an Empirical Model
nm, 1 nm bins, 60-second resolution
Models solar irradiance variations due to solar cycle, solar rotation, as well as both the impulsive and gradual phases of solar flares
Daily Proxies: MgII c/w, Ly, 30.5 nm, F10.7, 36.5 nm, and 0-4 nm.
Flare Proxies: GOES nm and the time derivative (Neupert Effect)

28. FISM Results FISM matches solar variability on timescales of:
Solar Cycle
Solar Rotation
Solar Flare
FISM will be greatly improved with EVE:
More flares (currently only 35 used)
Longer timescales for full spectrum and for proxies
Higher spectral resolution (0.1 nm?)

29. LISIRD

30. Potential Collaborations/Validations
TIMED-SEE XPS and EGS:
XPS overlaps: 0-10 nm
EGS overlaps: nm, Ly-
TIMED mission extended through 2010
TIMED observes for 3 minutes out of every 96 minute orbit
SORCE:
SOLSTICE overlaps: Ly- and nm
SIM overlaps: nm
SORCE prime mission is through 2008
SORCE observes for about ~60 minutes out of every 90 minute orbit
SDO-EVE:
ESP overlaps: nm
MEGS overlaps: 0-20 nm, nm, and Ly-, and SWAP bandpass
SDO due to launch August 2008 for 5 year mission
SDO-EVE will observe continuously from GEO
Sounding rockets:
flights of XPS and EVE rocket instruments planned in October 2006 and regularly after launch of SDO (2008).
FISM:
Model can be used to generate full spectrum from Chromospheric, Transition-Region, Coronal, and Hot Coronal proxies. Could be tuned to use LYRA bandpasses.