The Swarm Satellite Constellation Application and Research Facility (SCARF) and Swarm data products
 Nils Olsen^{1}Email author,
 Eigil FriisChristensen^{1},
 Rune Floberghagen^{2},
 Patrick Alken^{3, 4},
 Ciaran D. Beggan^{5},
 Arnaud Chulliat^{3},
 Eelco Doornbos^{6},
 João Teixeira da Encarnação^{6},
 Brian Hamilton^{5},
 Gauthier Hulot^{3},
 Jose van den IJssel^{6},
 Alexey Kuvshinov^{7},
 Vincent Lesur^{8},
 Hermann Lühr^{8},
 Susan Macmillan^{5},
 Stefan Maus^{4},
 Max Noja^{8},
 Poul Erik H. Olsen^{1},
 Jaeheung Park^{8},
 Gernot Plank^{9},
 Christoph Püthe^{7},
 Jan Rauberg^{8},
 Patricia Ritter^{8},
 Martin Rother^{8},
 Terence J. Sabaka^{10},
 Reyko Schachtschneider^{8},
 Olivier Sirol^{3},
 Claudia Stolle^{1, 8},
 Erwan Thébault^{3},
 Alan W. P. Thomson^{5},
 Lars TøffnerClausen^{1},
 Jakub Velímský^{11},
 Pierre Vigneron^{3} and
 Pieter N. Visser^{6}
DOI: 10.5047/eps.2013.07.001
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB. 2013
Received: 30 March 2013
Accepted: 1 July 2013
Published: 22 November 2013
Abstract
Swarm, a threesatellite constellation to study the dynamics of the Earth’s magnetic field and its interactions with the Earth system, is expected to be launched in late 2013. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution, in order to gain new insights into the Earth system by improving our understanding of the Earth’s interior and environment. In order to derive advanced models of the geomagnetic field (and other higherlevel data products) it is necessary to take explicit advantage of the constellation aspect of Swarm. The Swarm SCARF (SatelliteConstellationApplication andResearchFacility) has been established with the goal of deriving Level2 products by combination of data from the three satellites, and of the various instruments. The present paper describes the Swarm input data products (Level1b and auxiliary data) used by SCARF, the various processing chains of SCARF, and the Level2 output data products determined by SCARF.
Key words
Earth’s magnetic field core field lithosphere ionosphere magnetosphere electromagnetic induction comprehensive inversion Swarm satellites1. Introduction
Swarm, a constellation mission comprising three identical satellites to study the dynamics of the Earth’s magnetic field and its interactions with the Earth system (FriisChristensen et al., 2006, 2008) is expected to be launched in late 2013. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution, in order to gain new insights into the Earth system by improving our understanding of the Earth’s interior and environment.
Each of the three Swarm satellites will make highprecision and highresolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer, plasma and electric field measurements. These observations will be provided as Level1b data, which are the calibrated and formatted time series of e.g. the magnetic field measurements taken by each of the three Swarm satellites. These Level1b data, as well as the higherLevel Swarm data products described in this paper, will be distributed by ESRIN (Frascati/I).
Swarm will simultaneously obtain a spacetime characterisation of both the internal field sources in the Earth and the ionosphericmagnetospheric current systems. The research objectives assigned to the mission are: (a) studies of core dynamics, geodynamo processes, and coremantle interaction; (b) mapping of the lithospheric magnetisation and its geological interpretation; (c) determination of the 3D electrical conductivity of the mantle; and (d) investigation of electric currents flowing in the magnetosphere and ionosphere.
A challenging part, however, is the separation of the various sources (in the core, lithosphere, ionosphere, magnetosphere etc.) which in total yields the measured magnetic field. A constellation consisting of several satellites, like Swarm, opens new possibilities for exploring the geomagnetic field from space beyond those achievable with singlesatellites. At first glance one would expect that using simultaneous data from N satellites results in a reduction of the error of geomagnetic field models by , since the amount of data is increased by N compared to one single satellite. This error reduction by of course only holds if the data are statistically independent, which is highly idealistic and unrealistic since the main limiting factor for improved field modelling is not the measurement error but the dynamic behaviour of external sources. Treating data from a constellation of N satellites in a “singlesatellite” approach thus typically results in an improvement of the model error by less than . However, if explicit advantage is taken of the constellation, there is some potential for model improvement better than . A constellation of three satellites can do more than three single satellites, and therefore a (SMART) combination of data from all three satellites, and of the various instruments, allows for taking full advantage of the Swarm constellation. Analysis of the Swarm data will greatly improve existing and provide new models of the nearEarth magnetic field of high resolution and authenticity compared to what is possible with singlesatellite missions like Ørsted (Olsen, 2007) and CHAMP (Reigber et al., 2005).
In recognition of the large effort needed to extract the various types of scientific information from the complex set of observations a group of institutions and organisations have joined the SMART consortium (SwarmMagnetic andAtmosphericResearchTeam). The purpose of the consortium is to contribute to the optimal science return from the Swarm mission by a coordinated effort to exploit the constellation aspects of this unique mission. This effort is obviously in accordance with ESA’s aim of providing the scientific community with the best possible products from the Swarm mission, and it was decided to establish a SwarmSCARF (SatelliteConstellationApplication andResearchFacility), with the purpose of deriving commonly used scientific models and quantities, the socalled Level2 products and make them available to the scientific community at large. Advanced Swarmderived models of the geomagnetic field and other Level2 data products are determined from the Level1b data and auxiliary (i.e. nonSwarm) data and provide the prospect of investigating hitherto undetected features of the Earth’s interior.
SCARF (sometimes also called “Level2 Processing S>ystem”, L2PS) comprises in its present form a joint effort between the six European partners: DTU (Lyngby/DK), TU Delft (Delft/NL), BGS (Edinburgh/GB), ETH (Zürich/CH), GFZ (Potsdam/D) and IPGP (Paris/F) with contributions from CUP (Prague/CZ), NOAA (Boulder/USA) and GSFC/NASA (Greenbelt/USA). The team behind SCARF has designed and implemented algorithms to derive advanced models of the geomagnetic field describing sources in the core, lithosphere, ionosphere and magnetosphere, models of the electrical conductivity of Earth’s mantle and time series of thermospheric wind and density at the positions of the Swarm satellites. These models, which are stateoftheart implementations of current knowledge, are intended to facilitate and increase the use of the Swarm data by a much wider community than the one represented in the SMART consortium itself.
The work performed by SCARF is a major extension on the “EndToEnd” mission simulation that has been performed during Phase A of the Swarm mission, the results of which have been published in a special issue (Vol. 58 No. 4, 2006) of Earth, Planets and Space (cf. Olsen et al., 2006 for an overview).
The present paper describes the Swarm input data products (Level1b and auxiliary data) used by SCARF, the various processing chains of SCARF, and the Level2 output data products determined by SCARF and distributed by ESA through the PDGS (Payload Data Ground Segment) at ESRIN.
The content of the paper is as follows: Section 2 summarizes the various Level1b data, with emphasis on the 1 Hz time series of the magnetic field observations. Section 3 describes the various processing chains and resulting Level2 data products. All processing chains have been tested using synthetic data from a full mission simulation; the creation of this synthetic data set is described in Section 4. Data processing timeline and data availability are discussed in Section 5.
2. Swarm Level1b Products
Content of Swarm Level1b Product MAGx_LR.
Element  Contents  Units 

Timestamp  Time of observation  CDF_EPOCH 
SyncStatus  Time reference information  — 
Latitude  Latitude of observation in the International Terrestrial Reference Frame (ITRF)  degree 
Longitude  Longitude of observation in the ITRF  degree 
Radius  Radius of observation in ITRF  m 
F  Magnetic field intensity  nT 
dF_AOCS  Magnetic stray field correction intensity related to attitude control magnetotorquers  nT 
dF_other  Magnetic stray field correction intensity of all other sources  nT 
F_error  Error estimate on magnetic field intensity  nT 
B_VFM  Magnetic field vector in the instrument frame of the VFM magnetometer  nT 
B_NEC  Magnetic field vector in the NEC (North, East, Center) frame  nT 
dB_AOCS  Magnetic stray field correction vector related to attitude control magnetotorquers (in VFM frame)  nT 
dB_other  Magnetic stray field correction vector of all other sources (in VFM frame)  nT 
B_error  Error estimates on magnetic field vector B_{VFM} (in VFM frame)  nT 
q_NEC CRF  Rotation from NEC frame to STR Common Reference Frame (CRF), quaternion (NEC ← CRF)  — 
Att_error  Error estimate on attitude information  degree/10^{3} 
Flags_F  Flags characterizing the magnetic field intensity measurement: spikes or gap in data, discrepancy between ASM and VFM, etc.  — 
Flags_B  Flags characterizing the magnetic field vector measurement B_{VFM} and B_{NEC}: spikes or gap in data, discrepancy between ASM and VFM, etc.  — 
Flags_q  Flags characterizing the attitude information: identification of active heads, blinding, etc.  — 
Flags_Platform  Flags characterizing the spacecraft platform information: thruster activation, lack of telemetry, etc.  — 
ASM Freq_Dev  ASM reference frequency calibration data deviation for ASM stability assessment  Hz^{1/2} 
The quality of Level1b magnetic and plasma products MAGx_LR and EFIx_PL can be inspected using quicklook products, essentially comprising various daily and missiontodate plots designed to reveal a range of possible measurement problems (Beggan et al., 2013).
The positions provided in the Level1b data are generated automatically as part of the Level1b processing as “Medium Precise Orbits” (MOD) with an expected accuracy not exceeding a few meters. In case higher precision of the position is needed (or for periods where the MOD automatic calculation yields less optimal results) it is recommended to use the positions provided by the “Precise Orbit Determination” (POD) chain (Level2 product SP3xCOM_2_) discussed in Section 3.2.
3. Swarm Level2 Data Processing and Products
Depending on the complexity of the processing, there are two types of Level2 products, which are called Cat1 and Cat2 products, respectively. Cat1 data processing involves complex algorithms to derive Level2 products describing specific sources of the Earth’s magnetic field like the lithospheric field or time series of the largescale magnetospheric signal. Cat1 products are derived by SCARF since scientific expertise is required during processing. In contrast, processing of Cat2 products is less demanding, and therefore these products are derived by ESA on a daily basis in ESA’s Swarm PDGS using algorithms designed by SCARF. The processing runs automatically, leading to product release with minimum delay; Cat2 products are tested for their near real time capability with processing delays of less than 1 hour. Cat2 products are therefore suitable e.g. for space weather applications (Stolle et al., 2013).
The Swarm Level2 products.
Science Objective  Name  Format  Description 

(needed for Level1b processing)  MSW_EUL_2_  ASCII  Time series of Euler angles describing transformation from STRCRF to VFM frame for all three Swarm satellites (3 × 3 Euler angles) 
Core field  MCO_SHA_2_  ASCII  Spherical harmonic model of the core field and its temporal variation 
Lithospheric field  MLI_SHA_2_  ASCII  Spherical harmonic model of the lithospheric field 
Electrical conductivity of the mantle  MIN_1DM_2_  ASCII  1D model of mantle conductivity 
MIN_3DM_2_  ASCII  3D model of mantle conductivity  
MCR_1DM_2_  ASCII  1D Cresponses  
MCR_3DM_2_  ASCII  3D Cresponse maps  
External current systems  MMA_SHA_2_  CDF  Spherical harmonic model of the largescale magnetospheric field and its Earthinduced counterpart 
MIO_SHA_2_  ASCII  Spherical harmonic model of the daily geomagnetic variation at middle latitudes (Sq) and low latitudes (EEJ)  
Precise Orbit Determination (POD)  SP3xCOM_2_  SP3  Time series of position and velocity of the center of mass for satellite x (x = A, BorC) 
ACCxCAL_2_  CDF  Accelerometer calibration parameters for satellite x  
ACCxPOD_2_  CDF  Time series of nongravitational accelerations estimated for satellite x  
Magnetic Forcing of the Upper Atmosphere  ACCx_AE 2_  CDF  Time series of calibrated and preprocessed accelerometer observations and of aerodynamic accelerations for satellite x 
DNSxWND_2_  CDF  Time series of neutral thermospheric density and wind speed for satellite x  
Earth environment and SpaceWeather (Cat2 products)  IBIxTMS_2F  CDF  Ionospheric bubble index for satellite x 
TECxTMS_2F  CDF  Time series of the ionospheric total electron content for satellite x  
FAC_TMS_2F  CDF  Time series of fieldaligned currents determined from combination of Swarm A and Swarm B  
FACxTMS_2F  CDF  Time series of fieldaligned currents (singlesatellite solution) for satellite x  
EEFxTMS_2F  CDF  Equatorial Electric Field for satellite x 
3.1 Level2 products related to main magnetic sources
In addition to auxiliary data, the processing also requires auxiliary models like the IGRF (AUX_IGR_2_) or more advanced models of the core field (AUX_COR_2_) and the lithospheric field (AUX_LIT_2_). Models of the electrical conductivity of the Earth’s mantle (AUX_MCM_2_) and of the surface conductance of oceans and sediments (AUX_OCM_2_) are used to account for secondary, Earthinduced contributions connected to the temporal variations of magnetospheric and ionospheric origin. Finally, a model of the magnetic signature of ocean tides (AUX_MTI_2_) is provided.
In the following we briefly discuss the various Level2 products.
Spherical Harmonic Models of the core, lithospheric, ionospheric and magnetospheric field. Models of the core field and its time changes are provided as spherical harmonic expansion coefficients in the Level2 product MCO_SHA_2_ (where “M” indicates that the product describes a Magnetic source, “CO” stands for COre field, “SHA” denotes that the model is given as an expansion of a Spherical Harmonic Analysis, and “2” refers to the fact that this is a Level2 data product. The last character, in this example “_”, indicates the generic form of the Level2 product; other values are “C” if the product is derived in the Comprehensive Inversion chain or “D” if the product is derived in one of the Dedicated Inversion chains.)
For the core field models these are chosen to be Nmin = 1, N_{max} = 18 and the time dependence of the Gauss coefficients is parametrized using Bsplines; however, the final product MCO_SHA_2_ contains a series of snapshot models (corresponding to order 6 splines and 6 months separation of the spline knots). Details of the data format, and how to transform back from the snapshot representation to the original spline representation, are given in the Level2 Product Definition Document (Swarm Level 2 Processing System Consortium, 2013).
Core field model version MCO_SHA_2C is derived in the Comprehensive Inversion chain (see Sabaka et al. (2013) for details), while model version MCO_SHA_2D is derived in the Dedicated Inversion chain (Rother et al., 2013).
A proper determination of the Euler anglesα, β, γ describing the rotation between the instrument frames of the vector magnetometer and star tracker (see Eq. (2)) is only possible inorbit. A preflight determination made on ground is limited e.g. by atmospheric turbulence to an accuracy of, say, 20 arcseconds since global data coverage is required in order to obtain Euler angles within a few arcseconds. This is only possible inorbit. A determination of the Euler angles by coestimation with all major contributions to the nearEarth magnetic field is made in the Comprehensive Inversion chain (Sabaka et al., 2013), and an independent determination is made in the Dedicated Core chain (Rother et al., 2013). The resulting Euler angles are provided as Level2 data product MSW_EUL_2_ (MSW_EUL_2C and MSW_EUL_2F) and will be used in the reprocessing of Level1b data by the PDGS.
Spherical Harmonic Models of the lithospheric field are provided in the Level2 product MLI_SHA_2_ (where “LI” stands for LIthospheric field). Similar to the core field products, model version MLI_SHA_2C is derived in the CI chain, while model MLI_SHA_2D is determined using the Revised Spherical Harmonic Cap method, as described in Thébault et al. (2013). The minimum, resp. maximum, spherical harmonic degree and order is N_{min} = 16 and N_{max} = 150.
A model of the nonpolar daily geomagnetic variation caused by ionospheric currents, including their variability with season and solar flux, is given in the Level2 product MIO_SHA_2_, where “IO” stands for IOnospheric field. Details of the dedicated chain leading to product version MIO_SHA_2D are given in Chulliat et al. (2013). Product version MIO_SHA_2C is derived in the CI chain.
Finally, timeseries of spherical harmonic expansion coefficients of the largescale magnetospheric field and its Earthinduced counterpart are provided in the Level2 product of generic name MMA_SHA_2_. As part of the CI chain time series of the magnetospheric and induced expansion coefficients are provided with a sampling rate of 90 minutes (corresponding approximately to the orbital period of the satellites) for degree n = 1 and order m = 0, and with a sampling rate of 6 hours for degrees up to n = 3 and order m = 0, 1 for the magnetospheric field and up to n =m = 5 for the induced field. The name of the resulting product is MMA_SHA_2C. The dedicated chain (Hamilton, 2013) for deriving a related product called MMA_SHA_2F contains time series of magnetospheric and induced fields for degree n = 1 and order m = 0, 1 with sampling rate of 90 minutes. (The last character “F” in the product name indicates that this is a fasttrack product which is provided without an independent regular validation as is the case for most other Level2 products).
Level2 data product MMA_SHA_2C of the largescale magnetospheric field and its Earthinduced counterpart is used to determine models of electrical conductivity of the mantle, regarding both its 1D structure (which means that conductivity is assumed to only vary with depth, resulting in Level2 product MIN_1DM_2_, see Püthe and Kuvshinov (2013a) for details) and lateral variations of conductivity (3D models, Level2 product MIN_3DM_2_). The latter is derived using two independent chains, working in the frequency domain, leading to product version MIN_3DM_2a (Püthe and Kuvshinov, 2013b), or in the time domain, leading to product version MIN_3DM_2b (Velímsky, 2013). Electromagnetic transfer functions (Cresponses) are also provided (Level2 products MCR_1DM_2_ and MCR_3DM_2_).
3.2 Level2 products related to acceleration, orbit determination and thermospheric wind and density
3.3 Level2 products related to the Earth environment and space weather (Cat2 products)
Figure 5 shows the processing chains that result in the Cat2 Level2 products (listed in the bottom part of Table 3). All Cat2 products are provided as daily CDF files (similar to most of the Level1b products) since they all contain timeseries of a certain geophysical quantity.
Time series of an Ionospheric Bubble Index (IBI), derived using magnetic and plasma observations from each of the three satellites, are provided in IBIxTMS_2F. Details of the processing can be found in Park et al. (2013). Time series of the ionospheric and plasmaspheric Total Electron Content (TEC) as determined by each of the three satellites are provided in the product TECxTMS_2F. The implemented algorithm for TEC determination is identical to that described by Noja et al. (2013). The processing schemes resulting in time series of FieldAligned Currents (FAC) as provided in FACxTMS_2F (single satellite solution), resp. FAC_TMS_2F (obtained by combining data from Swarm A and B) are described in Ritter et al. (2013).
Dayside Eastward Equatorial Electric Field (EEF) values are derived for each equatorial crossing of each satellite (x = A, B, or C) and are provided in the product EEFxTMS_2F. More details on that chain are given in Alken et al. (2013).
4. Development and Test of the SwarmSCARF

Difference in spectra, degree error, and accumulated error. The MauersbergerLowes spectrum (degree variance)of the differences between the true (i.e. input) and the estimated model coefficients, , in combination with the spectrum of the input model, has been used to evaluate an estimated model. Degree error is defined as , and accumulated error at degree N is defined as .(5)

Degree correlation(Langel and Hinze, 1998, eq. (4.23)), where and hm e are from the estimated model and and are from the input model, has also been used to evaluate a spherical harmonic model. Models are considered compatible up to that degree n where ρ_{ n } drops below 0.7.(6)

Sensitivity matrix is the relative error of each coefficient in a degree versus order matrix:S(n,m) represents the percentage degreenormalized error in a recovered coefficient of degree n and order m.(7)

Global maps of field differences (for instance of B_{ r }) between the input and the estimated model are used to find geographically confined deficiencies in the estimated models, for instance in connection with the polar gaps.

Finally, the quality of time series (like those of the magnetospheric and induced spherical harmonic expansion coefficient) is assessed for various target periods using Squared Coherency coh^{2}: If F (ω) and G (ω) are the Fourier transform of the two time series f (t) and g(t) and F (ω)* is the complex conjugate of F(ω) then squared coherency at frequency ω is defined aswith ⟨F(ω)G (ω)*⟩ and ⟨G(ω)F (ω)*⟩ as the crossspectra and ⟨F(ω)F(ω)*⟩ and ⟨G(ω)G(ω)*⟩ as the autospectra of f(t),g(t) (e.g. eq. (20) of Olsen, 1998).(8)
Product requirements for magnetic Level2 products.
Product  Target Requirement  Threshold Requirement 

Core field (MCO), first time derivative (secular variation) at ground, n = 216, averaged over time  1 nT/yr  3 nT/yr 
Lithospheric field (MLI), accumulated error at ground, n = 16–150  40 nT  120 nT 
Ionospheric field (MIO), average relative error on ground  10% globally  10% at magnetic latitudes below ±55° 
Magnetospheric field (MMA)  Squared coherency coh^{2} > 0.8, though > 0.95 for n = 1  Squared coherency coh^{2} > 0.8, though > 0.75 for n = 1 
Mantle conductivity (MIN)  1/2 order of magnitude error, though 1/4 order of magnitude at depths 400–1500 km  1 order of magnitude error, though 1/2 order of magnitude at depths 400–1500 km 
At the beginning of the SCARF activity the launch of the Swarm satellites was still scheduled for 2010. In order to have similar ambient conditions, but access to actual input values to parametrize e.g. atmospheric drag or Earth rotation variations, we simulated a launch on July 1, 1998, 00:00 UT, which is approximately one solar cycle (11 years) before the anticipated launch in 2010.
The performed simulation is described in more detail in Olsen et al. (2007), which is an extension of the work of Olsen et al. (2006). In a first step we calculated synthetic orbits. We assumed all three satellites to be in circular nearpolar orbits with injection altitude of h_{0} = 450 km altitude and orbital inclination i = 87.4° for the lower pair (Swarm satellites A and B) and of h_{0} = 530 km altitude and orbital inclination i = 88° for the third satellite Swarm C. The two lower satellites were assumed separated in longitude by 1.4°. They are not exactly sidebyside (which would imply collision risk near the poles) but are shifted alongtrack by a time lag between 2 and 10 seconds. This simulates the requirement that “The maximum time difference between Swarm A and Swarm B when crossing the equator shall be 10 seconds”. The chosen orbital configuration is similar (though not identical) to the one that is presently foreseen for Swarm (h_{0} = 460 km and i = 87.35° for Swarm A and B; h_{0} = 530 km and i = 87.95° for Swarm C, and a Local Time of the Ascending Node of about 14:30).
Magnetic field data generation follows mainly the approach described in Olsen et al. (2006) with updates given in Olsen et al. (2007). The various input models have been designed in the following way: The core field is taken from the GRIMM model (Lesur et al., 2010) for the years 2003 to 2008, but shifted by 5 years (i.e. to 1998.0 to 2003.0) in order to be compatible with the simulation period. The lithospheric input model contains spherical harmonic expansion coefficients up to degree and order 250. Degrees n = 14 and 15 are taken from model POMME6.1, degrees n = 16 to 90 are taken from model MF7, and degrees 91 to 250 are taken from model NGDC720 (version 3p1) scaled by factor 1.1. See http://geomag.org/models/index.html for more information on these models. The magnetospheric field contribution is simulated using an hourbyhour spherical harmonic analysis of worldwide distributed observatory hourly mean values of the years 19972002 in dipolelatitude and magnetic local time. Expansion coefficients of degrees n = 1,…, 3 and order m = 0,…, 1 have been determined. Secondary, Earthinduced fields are determined (up to n = 15) from those primary coefficients using the 3D mantle conductivity model, including oceans, discussed in Kuvshinov et al. (2006). The input model describing the ionospheric primary field is taken from CM4 (Sabaka et al., 2004) while the secondary, induced, field is calculated from those primary coefficients using the same 3D mantle conductivity model as for the magnetospheric induced field. Finally, we added synthetic noise based on CHAMP experience. We assumed correlated random noise of standard deviation (0.1 0.07, 0.07) nT for (B_{n}, B_{E}, B_{C}), in agreement with the Swarm performance requirements.
The magnetic field vector in the Level1b CDF files is given both in the NEC coordinate frame and in the VFM frame of the vector magnetometer. In order to transform the synthetic data to the VFM frame we have arbitrarily chosen the (input) Euler angles (α = −1724, β = 3488,γ = −6184) arcsecs for Swarm A, (α = 808,β = −434,γ = −1234) arcsecs for Swarm B and (α = 2222,β = 2991,γ = 3115) arcsecs for Swarm C.
The various input (reference) models are available at ftp.space.dtu.dk/data/ magnetic satellites / Swarm/ SCARF/TDS 1/ Reference/ while the synthetic 1 Hz Level1b data product MAGx_LR files can be found at ftp.space. dtu.dk/ data /magneticsatellites/Swarm/ SCARF/TDS 1/Level1b/Mag/. Further details of the results of the closedloop modelling tests to check each chain meets the performance requirements can be found in the respective references and papers in this volume.
5. Swarm Processing Timeline and Data Availability

Three days (72 hours) after downlink
Swarm Level1b data are processed

Next working day
Swarm Level2 QuickLook (MAGx_QL_2_ and EFIx_QL_2_), FastTrack Magnetospheric (MMA_SHA_2F) and all Cat2 data products (which require up to 2 hours of processing time) are processed

Up to three weeks later
Swarm Level2 Products regarding Precise Orbit Determination (SP3xCOM_2_), Accelerometer data (ACCxCAL_2_, ACCxPOD_2_, ACCx_AE_2_), and Thermospheric (Neutral) Density and Winds (DNSxWND_2_), are processed

Every three months
Swarm Level2 FastTrack core field and Euler angles products (MCO_SHA_2F and MSW_EUL_2F) are processed

Every year
Every yearplus a few extra times in reduced form during the first year of the mission—the Swarm Level2 magnetic models are estimated and evaluated. The estimations are performed in two parallel processing chains:
The Comprehensive Inversion (MSW_EUL_2C, MCO_SHA_2C, MLI_SHA_2C, MMA_SHA_2C, MIO_SHA_2C) and Mantle Conductivity estimations (MIN_1DM, MIN_3DM, MCR_1DM, MCR_3DM) each with a processing time of one month

The Dedicated Inversions consisting of (in sequence, each step with a processing time of one month)

* Core field inversion (MCO_SHA_2D)

* Lithospheric field inversion (MLI_SHA_2D)

* Ionospheric field inversion (MIO_SHA_2D).


All estimated models are subject to an evaluation and when parallel models are available—crosscomparisons which will be documented in the Swarm Level2 Validation Products (Myy_VAL_2 _) with a processing time of up to one month.
Level1b and Level2 data are available at http://earth.esa.int/Swarm.
6. Conclusions
The Swarm mission is devoted to provide the best ever absolute measurements of the geomagnetic field. Its various instruments have been selected in order to optimize the scientific interpretation of the measurements in terms of the various sources of the magnetic field. In recognition of the large effort needed to extract the various types of scientific information from the complex set of observations a group of institutions and organisations have joined the SMART consortium (SwarmMagnetic andAtmosphericResearchTeam). The consortium has decided to contribute to the optimal science return from the mission by supporting the creation of a SwarmSCARF (SatelliteConstellationApplication andResearchFacility), with the purpose of deriving commonly used scientific models and parameters, the socalled Level2 products and make them available to the scientific community at large.
During the 3year long development phase of SCARF the various processing chains have been optimized and thoroughly tested, demonstrating that the facility is ready to enter the data exploitation phase and process real Swarm data. It is believed that some of the results of the SCARF exercise may also be of relevance for future Earth Science constellation missions that undoubtedly will be implemented.
List of Acronyms
ASM  Absolute Scalar Magnetometer (instrument) 
CDF  Common Data Format (Goucher and Mathews, 1994) 
CI  Comprehensive Inversion 
CRF  Common Reference Frame (of Star Tracker) 
DI  Dedicated Inversion 
EFI  Electric Field Instrument (LP and TII) 
FAC  FieldAligned Currents 
GPS  Global Position System (Receiver) 
ITRF  International Terrestrial Reference Frame 
LP  Langmuir Probe (instrument) 
NEC  North, East, Center coordinate frame 
MOD  Medium Precise Orbit Determination 
POD  Precise Orbit Determination 
PDGS  Payload Data Ground Segment 
RINEX  Receiver Independent Exchange Format (Gurtner and Estery, 2007) 
SP3  National Geodetic Survey Standard GPS Format (Hilla, 2007) 
STR  Star Tracker (instrument) 
TEC  Total Electron Content of ionosphere 
TII  Thermal Ion Imager (instrument) 
VFM  Vector Field Magnetometer (instrument) 
Declarations
Acknowledgments
The Development of Swarm SCARF has been funded by ESA through contract No. 4000102140/10/NL/JA.
Authors’ Affiliations
References
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