SMOS L1 Sun BT Validation against on-ground radio-telescope network Daniele Casella, Raffaele Crapolicchio, Emiliano Capolongo
Background Focus : SMOS L1b Sun BT Objectives: Evaluate the improvements of new processors Understand the utility and value of these data for the study of the Sun BACKGROUND: European Space Weather Week 12 (2015) Living Plant Symposium 2016 European Space Weather Week 14 (2017) The new L1OP processor has not (yet) been delivered Most of the analysis comes from the preliminary work done by Emiliano Capolongo during his Master thesis with the supervision of Raffaele Crapolicchio.
SMOS SMOS : ESA Earth Explorer dedicated to soil moisture and ocean salinity measurement Launch 2009 Sun-Syncronous orbit MIRAS: Microwave Imaging Radiometer using Aperture Synthesis Passive microwave 2D interferometeric radiometer Full polarimetric Operating at 1.413 GHz (21 cm)
MIRAS The MIRAS antenna array is formed by three arms 120 apart, with 23 equally spaced antennas each. Replicas DFT Basic Period Alias-free FOV Replicas Earth sky Horizon Direct Sun The brightness temperature image reconstruction is performed through a Fourier synthesis process of the cross correlations measured by pair of elements in the array. The Y-array configuration leads to an hexagonal sampling of the spatial frequency domain. Part of the FoV is affected by aliasing. Extended Alias-free FOV Replicas The alias-free FoV can be suitably extended over regions where the Sky alias is present to obtain an extended alias-free FoV (EAF-FoV) Direct Sun appears in an image replica in the Extended FOV
How SMOS sees the Sun Signal originated from the Sun: Contamination to be removed Strongest source of contamination Highly variable Appears in nearly 97% of the snapshots Sun appears in an image replica due to aliasing -> superimposed to an earth image
Why validate the Sun BT The solar radio emissions indicate the strength of the solar activity, Help to predict the arrival of high energy solar protons at the Earth, which can: degrade solar panels of spacecrafts, cause transpolar HF circuits to become disrupted, produce different satellites problems, power grid failures. Interference to man-made electromagnetic systems (e.g., HF radio blackout, radar interference, GPS geolocation errors). A strong burst on the 1415 MHz frequency is an indicator of GPS satellite signal lost.
Ground-based observations US Air Force Radio Solar Telescope Network (RSTN) Palehua, Sagmore Hill, San Vito, Learmoth Nobeyama Bleien Humain Humain Bleien Nobeyama
Sun Radio Emission Basic component Sun without spots ~6000 K Slow Varying Component from active regions Transient Component from Flare Bursts Bursts can exceed the quiet Sun background by several orders of magnitude The higher the frequency the lower the height of the Sun atmosphere layer observed
From SFU to BT Radio telescopes measure spectral flux density (F s ) in Solar Flux Units (SFU) 1 SFU = 10 22 W m 2 Hz 1 BT ( T d ) has been calculated by inverting: B λ Plank function k B Boltzmann constant λ wavelength Ω s is the solid angle of the Sun estimated by: Rs = 695,700 km (Earth-Sun distance) (Sun radius) Estimating the radius of the emitting region of the Sun in the microwave is non trivial Especially with Flares!
Solar Flares 1
Solar Flares 2 High correlation Variable scale factor
Solar Flares 3 Very high correlation: With strong and weak events With old and very recent events With various ground based radio telescopes Date and Time of Event X-ray Solar Flare Class Correlation Coefficient ground -based 15/02/2011 ~01:45 X 2.2 0.857 RSTN 09/08/2011 ~08:05 X6.9 0.984 RSTN 24/09/2011 ~13:15 M7.1 0.845 RSTN 23/01/2012 ~04:00 M8.7 0.994 RSTN 17/05/2012 ~01:47 M5.1 0.943 RSTN 12/07/2012 ~16:50 X1.4 0.984 RSTN 06/09/2017 ~12:00 X9.3 0.997 Humain 07/09/2017 ~09:30 M1.4 0.975 Humain 07/09/2017 ~14:30 X1.3 0.983 Humain
SFU Intercalibration issues Observations from various radiotelescopes during 17/05/2012 RSTN measurements are usually between ±10% w.r.t each other Data gaps appears in presence of recalibration of the telescope (every day around local noon for RSTN) and severe weather Sun rise and sunset measurements should be removed
Scale Factor Long term cal/val Preliminary results for Quite sun Learmonth Telescope only Data samples over 3 years The Scale factor is strongly related with the Sun positions w.r.t. the MIRAS antenna
Summary and future work SMOS Sun BT is strongly correlated with ground based observations. The scale factor between ground measurements and SMOS is strongly related to the Sun position in the antenna reference frame (Direct Sun Direction). Future Work: Generation of SMOS and ground based dataset for Sun BT Cal/Val. Evaluate the quality of the SMOS Sun BT information: Sensitivity to Sun angle Sensitivity to background (Land/Sea/Ice) Stokes parameter T3,T4 Quiet and active Sun Measurements of the Sun in the back Propose improvements for a future tailored specific processing for the generation of a dedicated SMOS Sun product for Space Weather applications.
BACKUP
Sun Self Estimation Algorithm A raw BT image is obtained by the inverse hexagonal Fourier transform: The instrument s response for a 1 K amplitude point-source in the Sun direction is computed The calibrated Sun BT is estimated rescaling the retrieved BT with the point source instrument response along the Sun direction The new processor (v.720) should estimate all the component of the Stokes vector.
RFI detection Discriminate RFI from Sun Flares is non trivial, some possibility may be: Compare simultaneous measurements from distant radio telescopes. Analyze the descending part of the curve.