Solar EUV Irradiance Observations: Status of the Current Set of GOES EUV

Sensor and Data

Rodney Viereck, NOAA SWPC Janet Machol, NOAA NGDC NCEI*

*NGDC is now part of the National Centers for Environmental Information (NCEI)

GOES NOP 13,14,15 Extreme Ultra-Violet Sensor

• Outline: – Observation Requirements – Measurement Requirements – Sensor Design – Sensor Performance – EUVS Status – EUVS Data Issues

Five EUV Bands

0 10 20 30 40 50 60 70 80 90 100 110 120 130 1401

10

100

1000

10000

100000

1000000

1E7

EUVEEUVD

EUVC

EUVBEUVA

Instru

ment

Resp

onse

Wavelength (nm)

-200-180-160-140-120-100-80-60-40-20020406080100120

Atmospheric Heating Rate

Heati

ng R

ate(de

g/hr)

0 20 40 60 80 100 12010-10

10-9

10-8

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

EUV-A EUV-B EUV-C EUV-D EUV-E

Wavelength (nm)

Original Design

Final Design

• Space Weather Requirements driven by…

– Ionospheric models (Communications, Navigations)

– Thermospheric models (Satellite drag) – Need something better than F10.7

• Original EUVS bands were well separated and covered much of the EUV spectrum.

• This design depended upon stable thin-film metallic filters two of which proved to be unstable.

• Final design relies upon grating angle to extend to longer wavelengths. Thus multiple orders are unavoidable.

• GOES 13 and 15 have these five band passes.

• GOES 14 was modified removing the C and D channels and replacing them with duplicates of the… EUV A and B channels

GOES 13,14, 15, EUVS Design

Electron Shielding Magnets

Zeolite Absorbers

Baffles

A

B

Shielding

Diffraction Grating

Silicon Diode Detectors

With Filters

22.5 cm

The Layout of two of the five channels of the GOES X-Ray Sensor

• Designed very similar to SOHO Solar EUV Monitor (Still providing good data after 18 years on orbit)

• Developed under and SBIR with NOAA

• First optical element is a diffraction grating made of thin wires (5000/mm). – Design is robust against

material contamination

GOES 13,14,15 EUV Observation Requirements (first flight of the GOES EUVS)

• Need to measure solar EUV irradiance for input into space weather models – Measurements relevant to thermosphere/ionosphere modeling

• Spectral Resolution – Must have at least 5 wavelength bands spanning 1 to 122 nm

• Cadence – Of order 30 seconds to capture flares and other impulsive variations

• Dynamic Range – Must cover full range of solar variability from solar min to solar max and solar

flares • Accuracies and stabilities to provide improvement over current

F10.7 daily measurements – Accuracy of +/-30% – Stability of +/- 5% over five years

GOES EUVS Coverage

EUV Flares

During the PLT period there were only two solar flares of significance. An M-2 class flare occurred in July 2006 and an X-9 class flare occurred in December 2006. The two phases of a flare… impulsive and gradual, are both clearly observable in the various channels

1E-9

1E-8

1E-7

1E-6

1E-5

XRS

Irrad

ianc

e(W

/m2 )

G12XRSLong G12XRSShrt G13XRSLong1 G13XRSShrt1

7/6/2006 19:00 7/6/2006 21:00 7/6/2006 23:00

0.0002

0.00040.00060.00070.00080.00090.00016

0.00018

0.000200.00200.00210.00220.00230.00240.00250.006

0.007

A Channel85%

C Channel

B Channel21%

Irrad

iance

(W/m

2 )

18%

D Channel15%

E Channel12%

12/5/2006 22:00 12/5/2006 23:00 12/5/2006 24:00

0.00060.00120.0018

0.0008

0.0010

0.00020

0.00025

0.0025

0.0030

0.0065

0.0070

0.0075

A Channel600%

C Channel

B Channel45%

Irrad

ianc

e (W

/m2 )

49%

D Channel38%

E Channel12%

X-9 Flare

M-2 Flare

EUVA Channel (5-17 nm)

EUVB Channel (30.4 nm)

EUV E-Channel (121 nm) • EUV Channel E (Lyman Alpha) sensors show signs of degradation

– Most likely due to filter degradation – Degradation can be removed with analysis (removing and exponential decay)

EUV Irradiance Proxy Model: • Stan_Bands = C0 + C1* MgII + C2*MgII_smooth + C3*F10.7 + C4*XRS_Short +

C5*XRS_Long + C6*EUVA + C7*EUVB + C8*EUVC + C9*EUVD + C10*EUVE

EUVS Status

• GOES 13: – Launched in Mid 2006 – Currently operating as Secondary XRS and EUVS – XRS failed during Post Launch Test (PLT)… but has now recovered. – Five Channel EUVS working well

• GOES 14: – Launched in Early 2009 – Currently in Storage – XRS working well – Three channel EUVS working well

• GOES 15: – Launched in Late 2009 – Currently operating as Primary XRS and EUVS – XRS working well – Five channel EUVS working well

• GOES R: – Launch ready in 2016

Backup Slides

GOES NOP Extreme Ultra-Violet Sensor (EUVS) and X-Ray Sensor (XRS)

EUVS Data Issue 1. • EUV Channel E (Lyman Alpha) sensors show signs of degradation

– Most likely due to filter degradation – Degradation can be removed with analysis

July 28, 2006 GOES-N PLT Weekly Report Slide 16

EUVS Issue 2. GOES 13 EUVS Pointing

• The average misalignment for the EUVS relative to the SXI is about 2.3 degrees.

• Corrections need to be applied to the EUVE channel but not the other EUV channels nor the XRS channels

• It is not yet clear how well this compensation will work.

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

0.4

0.6

0.8

1.0

15:04:46.6715:20:26.95

14:49:51.9714:34:11.69

EUVE Data SXI Centered

Nor

mal

ized

Cou

nts

Azimuth Angle

Solar position in the SXI FOV when the sun is centered for the EUVE channel

Solar position in the EUVE channel when the sun is centered in the SXI FOV

July 28, 2006 GOES-N PLT Weekly Report Slide 17

EUVS Issues 3. EUVA Channel Heater Noise

7/22/2006 12:00 7/22/2006 18:00 7/23/2006 00:00

25050

25100

25150

25200

25250

7.88.08.28.48.68.89.09.2

EUVA

Cou

nts

SXI S

uppo

rt Te

mpe

ratu

re

8/14/2006 8/15/2006

25400

25500

25600

8/14/2006 8/15/20064.04.24.44.64.85.05.25.45.65.8

EUVA

Cou

nts

IMP

Tem

pera

ture

(deg

) IMP Temperature

SXI Temperature

Data filter using SXI temperatures allows much of the noise to be removed.

The EUVS temperature sensors and the Image Mounting Platform Temperature sensors do not have the resolution required

Before

After

From Dave Uetrecht

Evidence of thermal interference in the EUVS data as shown by a strong correlation between temperature and EUVA signal.

July 28, 2006 GOES-N PLT Weekly Report Slide 18

Unexpected Feature in the EUVS Data: Diurnal Signal in EUVE Channel

• EUVS – Dip of 3% – Every day at 0600 UT – Increasing in depth toward eclipse

• Conclusion – Not due to pointing errors (timing offset) – Dips are the absorption of the solar H Lyman

Alpha signal by the cloud of hydrogen surrounding Earth (Geocorona).

– This will provide direct measure of the density of the geocorona over seasons and decades

EUVE E Channel

SXI HASS Azimuth Angle

Six hour offset

Signal dips in EUVE channel are solar occultation by cloud of hydrogen around Earth (geocorona) Extends up 2000 km or more from the surface. Absorbs H Ly Alpha

• Do we need to measure the entire EUV spectrum?

• Can we measure just a few spectral lines and model the rest?

• TIMED SEE data show that we can measure a few spectral lines and model the rest of the EUV spectrum

• SDO EVE data will further refine the model

• GOES R will measure a few spectral lines very well and we will model the rest.

• MgII • H Lyman Alpha • He 30.4 • Coronal Lines

0 20 40 60 80 100 1200.0

0.1

0.2

F10 + F10(81 day Avg)

Mg II + F10 + F10(81 day Avg)

Five Bands + Mg II + F10 + F10(81 day Avg)

Five Lines + Mg II + F10 + F10(81 day Avg)

Stan

dard

Devia

tion

Wavelength (nm)

0 20 40 60 80 100 12010-10

10-9

10-8

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

EUV-A EUV-B EUV-C EUV-D EUV-E

Wavelength (nm)

GOES R EUVS: Measuring vs Modeling

the EUV Irradiance

This plot shows the errors induced by using proxies, bands, or just a few spectral lines

XRS/EUVS Measurement Requirements (1 of 3)

• 9.1.2.1 Wavelength Ranges and Threshold Sensitivities - Two X-ray channels are required to observe solar fluxes in the 0.05 to 0.3 nm and the 0.1 to 0.8 nm bands, respectively. At least five EUV channels are required to observe solar fluxes in the 10-125 nm range. The preferred and the acceptable range of values for the lower and upper XRS/EUV channel band edges are provided in Table 9.1.2.1.

Thresholds: The instrument shall be capable of measuring fluxes above a threshold sensitivity for each of the seven channels listed in Table 9.1.2.1. Threshold sensitivity is defined as the minimum in-band solar flux that will produce a mean signal equal to the standard deviation of the data (instrumental noise) over a 10-second interval. For the two X-ray channels, the in-band solar spectrum varies several orders of magnitude with wavelength as shown in Figure 9.1.2.1 (from Mewe and Groenschild, 1981, Astron. Astrophys. Suppl. Ser., vol. 45, pp 11-52). A solar spectrum at 2 x 106 K shall be assumed for the two X-ray channels for threshold sensitivity determination. For the EUV channels, the solar spectrum is not a strong function of wavelength and a flat spectrum may be assumed within each channel for determining the threshold sensitivity. The out-of-band rejection shall be such that < 10% of the observed signal comes from out-of-band for a typical solar spectrum. Alternatively, a method of measuring out-of-band contamination shall be provided. Over the duration of the mission, the instrument response shall not change by > 5% due to deposition of outgassed materials onto optical surfaces.

Channel Preferred Wavelength Range (nm)

Lower Upper

Acceptable Lower Band Edge Range

(nm)

Acceptable Upper Band Edge Range

(nm) XRS-A 0.05 0.4 0 to 0.1 0.3 to 0.5

XRS-B 0.1 0.8 0 to 0.2 0.75 to 1.2

EUV-A 10 25 5 to 12 15 to 27

EUV-B 25 40 17 to 27 34 to 43

EUV-C 40 65 10 to 52 62 to 70

EUV-D 65 100 10 to 85 20 to 110

EUV-E 119 124 114 to 120 123 to 129 (modified to allow for multiple orders in C and D channels)

XRS/EUVS Measurement Requirements (2 of 3)

• 9.1.2.2 Threshold Fluxes and Dynamic Range - The instrument shall be capable of measuring fluxes for each channel over the specified dynamic ranges given in Table 9.1.2.2, when the fluxes are above the given thresholds.

• 9.1.2.3 Flux Resolution and Response - For the two X-ray channels, the resolution of the energy flux measurements shall be < 2% of the detected flux for fluxes > 20 times the threshold fluxes specified in Table 9.1.2.2. The telemetered data shall be a monotonic function of the input fluxes with deviations from a monotonic response function being less than the flux resolution when the incident flux exceeds 20 times the threshold flux. For the EUV channels the resolution of the energy flux measurement shall be < 0.25% of the full scale value.

• 9.1.2.4 Electron Environment - The minimum performance of the Solar X-ray and EUV sensor shall not be compromised by the presence of the anticipated worst case natural electron environment. To allow for the fact that the trapped particle population is not isotropically distributed, a 2% peak-to-peak sinusoidal variation with angle shall be assumed superimposed on the average electron environment. The representation for the worst case natural environment assumes isotropic flux with the spectral distribution shown in Table 9.1.2.4.

• 9.1.2.5 Temporal Resolution - The temporal resolution of the X-ray fluxes shall be at least 3 seconds and the flux values shall be transmitted to ground in real-time. The time delay between flux measurements in the two X-ray channels shall be less than 0.1 second. The instrument response to an instantaneous change in X-ray flux (a step function) shall be such that the telemetered output of each channel shall be within 10% of its final value within the specified temporal resolution. The analytical channel response function shall be specified by the spacecraft contractor to sufficient accuracy to allow for possible ground correction of the data. Each EUV channel shall be sampled at least every 30 seconds.

• • 9.1.2.6 Angular Response - The instrument response,

including the combined effect of spacecraft pointing and sensor field-of-view (FOV), shall not deviate by more than 5%, with a goal of 2%, for point sources of constant flux within 20 arc-minutes of the solar disk center.

•

XRS/EUVS Measurement Requirements (3 of 3)

• Pointing Knowledge - The spacecraft contractor shall provide a method of determining the XRS/EUV mechanical pointing with respect to the Sun-center. This pointing information shall be provided at the same cadence as the measurements made by the XRS/EUV, and shall be sufficient to determine unambiguously the direction to the Sun whenever the Sun center is within ±10o of the mechanical axis of the XRS/EUV FOV (i.e., multiple viewing angles should not give the same output signal). The accuracy of the XRS/EUV pointing determination with respect to the Sun-center shall be ±2 arcminutes with a resolution of ±1 arcmin when the Sun-center is within ±2o of the mechanical axis of the XRS/EUV FOV. This high accuracy and resolution is not required at viewing angles > 2o. The spacecraft contractor shall provide a calibration of the XRS/EUV FOV with respect to the mechanical axis used for the pointing determination.

• 9.1.2.8 In-flight Calibration - A calibration mode shall be provided by ground command for determining electronic processing gain to an accuracy of 2% for all channels and for verifying basic instrument operation. This calibration shall be traceable to incident flux through the detector pre-flight calibration. The calibration shall be both self-terminating and able to be terminated by ground command.

• 9.1.2.9 Pre-flight Calibration - Calibration of the instrument response to flux shall cover the full dynamic range and expected range of sensor temperatures. Trend sensitivity data shall be provided throughout the instrument and spacecraft level tests.

• • 9.1.2.9.1 Wavelength Response - The wavelength

response of each channel shall be specified to an accuracy of ±5%. The instrument shall be calibrated at sufficient wavelengths to adequately characterize the wavelength response from each detector component with a wavelength-dependent response. An analysis of the uncertainties and errors of each component shall be provided to verify that the number of calibration wavelengths is sufficient to adequately characterize the relative wavelength response to an accuracy of ±5%.

• 9.1.2.9.2 Absolute Response - The accuracy of the telemetered X-ray flux data shall be demonstrated by analysis and/or test to be better than ±20% with a goal of ±10% of the actual flux for flux values greater than 20 times threshold. The accuracy of the telemetered EUV flux data shall be better than ±20% with a goal +/- 10% of the actual flux. (MOD 32, CCR6057A)