GSICS/CEOS web meeting on Reference Solar Spectrum 2016-12-01

Agenda

1. NPL, Nigel Fox CEOS IVOS Reference Solar Irradiance spectrum

2. NASA. D. Doelling, GSICS Considerations for Recommending a Reference Solar Spectrum

3. IUP Bremen, K. Bramstedt, The SCIAMACHY solar spectrum

4. NOAA, L. Flynn, Comparison of the Aura/OMI, SORCE SIM, and SORCE SOLSTICE solar spectrum

5. EUMETSAT, Marcel Dobber, OMI Solar Spectra

   ASCII version of the solar reference spectrum - High-resolution solar reference spectrum derived from comparisons with EOS-AURA Ozone Monitoring Instrument (OMI) sun irradiance measurements.

   M. Dobber et al., Solar Physics volume 249, no. 2, 281-291, June 2008, DOI 10.1007/s11207-008-9187-7.

   Spectral range: 202-600 nm, radiometric accuracy about 4%, spectral resolution 0.025 nm, spectral sampling 0.01 nm, wavelength accuracy 0.002 nm over range 250-550 nm.

6. RMIB, S. Dewitte, Solar reference spectra from the Solspec instruments

See also GSICS Wiki topic ReferenceSolarSpectrum.

Attendees

Guest Chair: Dave Doelling (NASA)

NPL: Nigel Fox

JMA: Masaya Takahashi, Arata Okuyama

ESA: Berit Ahlers, Ben Veihelmann

CNES: Bertrand Fougnie

KMA: Dohyeong Kim, Hyesook Lee

USGS: Esad Micijevic

Fabio ?

BC: Grit Kirches

NASA: Glen Jaross, David Flittner, Dave Doelling, Amit Angal, Ben Scarino, Greg Kopp, Colin Seftor

IUP Bremen: Klaus Bramsted & Tina Hilbig

JAXA: Kei Shiomi, Hiroshi Murakami

NOAA: Larry Flynn, Sri Madhavan, Manik Bali, Haifeng Qian, Fangfang Yu, Fred Wu

CMA: Li Yuan, Lin Chen

EUMETSAT: Marcel Dobber, Rose Munro, Sebastien Wagner, Tim Hewison, Frank Ruethrich & Viju John

VITO: Sindy Sterckx

RMIB: Steven Dewitte

ESS: Thijs Krijger & Ralph Snel

PMOD/WRC: Werner Schmutz, Margit Haberreiter

DLR: Sander Slijkhuis

Solar spectra web meeting introduction

David Doelling and Nigel Fox gave introduction presentations to start the process of recommending a solar-spectra for GSICS and CEOS. Nigel commented that Thuillier-2003 was the last CEOS recommended dataset. There have been new sensors and improvements in the last 13 years that the solar community would want to take advantage in order to come up with a new recommended reference solar spectra. We would like to get consensus among the solar spectra community in the short order.

Discussion and Outcome

Many thanks to K. Bramstedt, L. Flynn, M. Dobber, and S. Dewitte (R. Snel) for their presentations and members of the web audience solar community for the helpful discussions.

It was recommended that the best approach was to split the solar spectra into two components, the UV portion 0.20µm or 0.25µm to ~0.45µm, and the visible/NIR/SWIR or non-UV spectra between 0.35µm to >2.5µm. We would then scale the two spectral intervals together using the overlap spectra. There will be some groups that will participate in both spectra.

The non-UV spectra will have <0.1% uncertainty due to solar cycle. This is well below the dataset spectral irradiance differences for some wavelengths. Most observed non-UV solar spectra usually are referenced to the solar minima during the solar cycle or quiet sun. The idea would be to find consensus among datasets based on their onboard calibration uncertainty that is strengths or weaknesses, which maybe a function of wavelength during a quiet sun. This was considered to be the quickest path to consensus or low hanging fruit. Need volunteer to analyze these datasets. We do not want to analyze various solar spectra at differing solar activity levels.

The UV spectra is a function of a short term 27-day solar rotation cycle and an 11-year solar cycle. To compare the UV datasets, the datasets must be averaged to a coarser spectral resolution and be tied to solar activity by a Mg II indicator. If a time dependent dataset is recommended than a dedicated updating mechanism must be in place.

It was also suggested to provide the highest spectral resolution dataset possible and a recommended way of downscaling the resolution.

Next Web Meeting

Set up next solar spectra web meeting for Jan 2017.

1. Steven Dewitte will re-present his powerpoint, due to technical difficulties he was unable to present
2. Greg Kopp will discuss his 3 submitted solar spectra.
3. Margit Haberreiter, SSI composite, which was developed within the European FP7 project SOLID
4. Odele Coddington, Solar Irradiance climate data record

Solar spectra datasets for consideration

If you would like provide a solar spectra dataset for this effort, please email

Tim.Hewison@eumetsat.int, david.r.doelling@nasa.gov, Nigel.Fox@npl.co.uk,

It will be posted on the GSICS solar spectra web page:

http://gsics.atmos.umd.edu/bin/view/Development/ReferenceSolarSpectrum

please provide the dataset name, a short description (one or two sentences), Reference citation or link, dataset link, and contact name.

This will allow for comparisons among datasets and a solar spectra archive for the satellite dataset providers, GSICS and CEOS members.

Steps to compare solar measurements from BUV (Backscatter Ultraviolet) instruments. (Larry Flynn)

•The first step is to catalog high spectral resolution solar reference spectra and agree on a common one to use for the project. (Or multiple candidates.)

•For each instrument, participants should provide the following datasets:

–Solar measurement for some specific date (wavelength scale, irradiance) (Or a time series of measurements)

–Wavelength scale and bandpass (Δλ, # of points, bandpass centers, normalized bandpass weights) (and time dependence if needed)

–Synthetic spectrum from common reference (wavelength scale, irradiance)

–Synthetic for wavelength scale perturbations (±0.01 nm) from common reference (wavelength scale, irradiance) (or wavelength shift model coefficients)

–Synthetic from alternative reference spectra (wavelength scale, irradiance)

–Solar activity pattern (wavelength, relative change)

–Mg II index (if 280 nm is covered) Mg II 279.6 Mg I 285.2 (date, index)

–Ca H/K index (if 391 nm to 399 nm is covered) CA II 393.4 and 396.8.

•Goals:

–Agreement at 1% on solar spectra relative to bandpass-convolved high resolution spectra as a transfer after identifying wavelength shifts and accounting for solar activity

–Long-term solar spectra drift and instrument degradation by using solar activity patterns (with internal confirmation from Mg II Indices and scale factors)