Solar radio observation from Soil Moisture and Ocean Salinity (SMOS) mission: a potential new dataset for space weather services

Raffaele Crapolicchio 1,2 Daniele Casella1, Christophe Marqué3, Nicolas Bergeot3, Jean-Marie Chevalier3

1 SERCO Italia S.p.A., 2 ESA ESRIN, 3 Royal Observatory of Belgiumraffaele.crapolicchio@esa.int

Intense solar radio bursts (SRBs) emitted at L-band frequencies are a source of radio frequencyinterference for Global Navigation Satellite Systems (GNSS) and consequently impact the qualityof the GNSS signal reception (Klobuchar et al., 1999 and Cerruti et al., 2008) (Figure 1). Suchspace weather events are critical for GNSS-based applications requiring real-time high-precisionpositioning (Sreeja et al., 2014). Although solar observatories routinely monitor solar radioemissions, the intensity and polarization of SRB at the specific GNSS frequencies (L1 at1575.41MHz and L2 at 1227.60MHz) are not determined in real-time.

1. Solar Radio Burst and GNSS

3. Comparison GNSS and SMOS

Conclusions• The direct comparison of GPS ΔC/N0 fade and SMOS Sun brightness temperature show very strong

correlations in the case studies where the SMOS 4th Stokes vector component shows right hand polarizedradiation (GPS-like polarisation).

• The monitoring of the solar radio emissions in terms of intensity and polarisation around the GNSSfrequencies with SMOS data available in near real time makes these dataset valuable for comparison withGNSS signal reception fades due to Solar Radio Bursts.

Reference1. J. Klobuchar, J. Kunches and A. VanDierendonck, “Eye on the ionosphere: Potential solar radio burst effects on GPS signal to noise”. GPS

Solutions, 19992. A. P. Cerruti, P. Kintner, D. Gary, A. Mannucci, R. Meyer, P. Doherty, and A. Coster, Effect of intense December 2006 solar radio bursts on

GPS receivers, Space Weather, 20083. V. Sreeja, M. Aquino, K. de Jong, and H. Visser, “Effect of the 24 September 2011 solar radio burst on precise point positioning service”,

Space Weather, 20144. B. Muhammad, V. Alberti, A. Marassi, E. Cianca, M. Messerotti, “Performance assessment of GPS receivers during the September 24, 2011

solar radio burst event”, J. Space Weather Space Clim. 20155. Camps, A., Vall-llossera, M., Duffo, N., Zapata,M., Corbella, I., Torres, F. & Barrena, V. (2004), Sun Effects in 2-D Aperture Synthesis

Radiometry Imaging and Their Cancelation, IEEE Trans. Geosci. Remote Sens., vol. 42, no. 6, 1161–11676. Crapolichio, R., Capolongo, E. & Bigazzi,A.(2016). Sun L-band brightness temperature estimate from soil moisture and ocean salinity

(SMOS) mission: a potential new space weather application for SMOS data. Living Planet Symposium. Vol. 740. 2016.

To address this issue, the Royal Observatory of Belgium(ROB) monitors in near-real time (updated every 15 min)the carrier-to-noise density (C/N0) observations from theGNSS EPN network. The monitoring allows detecting andquantifying the impact of SRBs on GNSS signal receptionat the L1 and L2 frequencies.

The estimated <ΔC/N0>L1,L2 from the real-time GNSSnetwork is used to provide scaled warnings (Figure 2) forthe GNSS application users via our website and alertemails. Summary of event are provided couple days after(Figure 3 and 4).

The solar radio bursts of the 06/09/2017 impacted the GPS signal reception atboth frequencies L1 and L2. On L1, two fades above 1dB-Hz were detected at12h01 and 12h05. On L2, a first fade above 3dB-Hz which could potentially affectthe GNSS application, occurred for 3 min with a maximum of -6.25±1.6dB-Hz at12h02. It was followed by a second lower fade above 1dB-Hz at 13h03. Foradditional information about the burst on a larger frequency spectrum see at SIDCHumain Radioastronomy Station.

Figure: <ΔC/N0>L2 time series at L2 frequency

Summary of event

Figure 3: Summary of SRB event on the GPS signal reception(ΔC/N0) during the 6th September 2017

Figure 1: From top to bottom : GPS fade of <C/N0> for the EPN network at a) L1 and b) L2 frequency together with the SMOS c) intensity (SUN BT I) and d) polarisation ratio (right-hand polarised SMOS SUN BT V/I <0) observation and with e) the satellite position during 4 SRB events (from left to right)

a)

b)

c)

d)

e)

Figure 2: Scaled SRB warning for GNSS users

Email alert

Figure 4: email alert of the 6th September 2017

Figure 1: GPS signal reception fade at L1 forthe stations of the EUREF Permanent Networkdue to the Solar Radio Burst of the 24th

September 2011

Soil Moisture and Ocean Salinity (SMOS) Sun polarimetric observations provide complementary information for space weather applications such as the real-time warning system for Global Navigation Satellite Systems (GNSS) signal service operated by Royal Observatory of Belgium – Solar Terrestrial centre of excellence. SMOS data has been used in 4 case studies of Solar Radio Bursts and compared with Global Positioning System signal anomalies that have been observed with different polarization.

2. SMOS observations of the Sun

The field of view (FoV) of each of these LICEF is large enough (Figure 4) to capture signals not onlyfrom the Earth but also its surrounding Sky including the Moon, the Sun and the Galaxy. The Y-arrayconfiguration leads to an hexagonal sampling of the spatial frequency domain. Part of the FoV isaffected by aliasing. Nonetheless, by specific processing task the alias-free FoV can be suitablyextended over regions where the Sky alias is present to obtain an extended alias-free FoV (EAF-FoV).The Brightness temperature of the Sun can be estimated from its alias position in the image EAF-FOV(Figure 5). By analysing several solar flares events we checked the capability of the SMOS dataset totrack the evolution of the solar radio burst flux in the radio band (Figure 6 and Figure 7).

ESA’s Soil Moisture and Ocean Salinity (SMOS) mission is dedicated to making global observations ofsoil moisture over land and sea surface salinity over oceans. SMOS is on a Sun-synchronous(6am/6pm), quasi-circular orbit with a mean altitude of 758 km and inclination of 98.44° (Figure 1).The payload of SMOS consists of the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS)instrument, a passive microwave 2-D interferometric full polarization radiometer, operating at 1.413GHz (wavelength of 21 cm). The MIRAS antenna array is formed by three arms 120° apart (Figure 2),with 23 equally spaced Lightweight Cost-Effective Front-End (LICEF) antennas each (Figure 3).

Figure 7: correlation in timebetween estimated SMOS Sunflux and the ground basedradio telescope measurementsis very high often exceeding 0.9

Sun L-band brightness temperatureSolar Radio Burst 17 May 2012

SMOS V620SMOS V720Reference radio-telescope

Figure 1: Orbit Figure 2: MIRAS payload Figure 4: Antenna PatternFigure 3: LICEF in the MIRAS hub

Earth sky Horizon

DFT Basic Period

Replicas

Replicas

Replicas

Alias-free FOV

Extended Alias-free FOV

Direct Sun

Figure 5: representation ofthe unit circle antenna,the closest six replicas, thepositions of the Sun.

Figure 6: temporal evolutionof SMOS and RSTN radio-telescope L-band Sunbrightness temperature