Computer Science – Sound
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsp54a..02e&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #SP54A-02
Computer Science
Sound
7538 Solar Irradiance, 7549 Ultraviolet Emissions, 7594 Instruments And Techniques
Scientific paper
Degradation of optics and detectors is a difficult technical issue for satellite-borne extreme ultraviolet (EUV) instrumentation, in particular for solar spectral irradiance monitors. Traditional techniques of tracking changes in instrument responsivities have included redundant channels, on-board sources, and sounding rocket underflights. Such methods can be costly, especially for long duration missions such as the NOAA GOES-R program, where the EUV Sensor (EUVS) must still meet stringent accuracy requirements as long as fifteen years after launch. We have developed an on-board means of determining instrument degradation for the upcoming GOES-R EUVS using the behavior of the solar emissions being measured. The key to this technique is the measurement of the Mg II core-to-wing ratio, a chromospheric index that does not require absolute calibration. With relationships between the Mg II index and other chromospheric emissions established with prior observations, the Mg II index can be used to correct irradiance measurements of other chromospheric emissions elsewhere in the solar spectrum that may be subject to long-term instrument degradation. Some of these chromospheric emissions, such as C III 117.5 nm and C II 133.5 nm, are close in wavelength to transition region emissions, such as H I 121.6 nm (Lyman-alpha) and Si IV/O IV 140.5 nm, allowing degradation to be estimated for the irradiances of these transition region emissions. Likewise, the corrected transition region proxies can then provide long-term variability of other transition region emissions at shorter wavelengths in the EUV, such as the He II 30.4 nm and He II 25.6 nm emissions. Finally, the proximity of these bootstrap-corrected transition region emissions to nearby coronal emissions, such as Fe XV 28.4 nm, allow us to transfer the degradation correction to some coronal emissions. Then accurate estimates of the solar spectral irradiance over the full EUV range can be made with corrected proxies representative of the chromosphere, transition region, and corona. We will present the details of this EUV bootstrap degradation tracking technique planned for the GOES-R EUVS and the validation of it using TIMED-SEE spectral irradiance measurements.
Eparvier Francis G.
Woods Thomas N.
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