Deriving VTEC Maps from SMOS Radiometric Data
"> Figure 1
<p>Faraday rotation angle (FRA) over the extended alias-free field of view (EAF-FoV): (<b>a</b>) database FRA, (<b>b</b>) systematic FRA error when considering the FRA value at boresight for the entire EAF-FoV.</p> "> Figure 2
<p>FRA in the Soil Moisture and Ocean Salinity (SMOS) boresight coordinates of 3 days in different periods: (<b>a</b>) descending orbits in March 2014 (high sun activity), (<b>b</b>) descending orbits in January 2011 (low sun activity), (<b>c</b>) ascending orbits in March 2014 (high sun activity), (<b>d</b>) ascending orbits in January 2011 (low sun activity).</p> "> Figure 3
<p>Latitude–time Hovmöller plots of the boresight FRA for the full mission for: (<b>a</b>) descending orbit, (<b>b</b>) ascending orbits.</p> "> Figure 4
<p>Typical open ocean Fresnel brightness temperature snapshots per polarization (left: X-pol, middle: Y-pol, right: third Stokes parameter). Top: Fresnel modeled brightness temperature (TB), middle: taking into account the FRA, bottom: adding the effect of noise in addition to the FRA.</p> "> Figure 5
<p>Vertical total electron content (VTEC) snapshots: (<b>a</b>) database VTEC, (<b>b</b>) its retrieved VTEC snapshot with pixels affected by the indetermination of Equation 3, (<b>c</b>) its retrieved VTEC filtering affected pixels, (<b>d</b>) another database VTEC snapshot, (<b>e</b>) its retrieved VTEC snapshot with pixels affected by the indetermination of Equation (1), (<b>f</b>) its retrieved VTEC filtering affected pixels.</p> "> Figure 6
<p>VTEC of a descendent orbit over the Pacific Ocean, March 20th, 2014: (<b>a</b>) database VTEC and (<b>b</b>) simulated VTEC retrieval.</p> "> Figure 7
<p>Root mean square error of the retrieved VTEC with respect to the database VTEC when optimizing (<b>a</b>) the size of the temporal filter with a coarse binning, (<b>b</b>) the size of the spatial filter with a coarse binning, setting an optimum temporal filter size, and (<b>c</b>) the size of the spatial filter with a fine binning, setting the temporal filter with the most optimum temporal filter size.</p> "> Figure 8
<p>VTEC of a descendent orbit over the Pacific Ocean, March 21st, 2011 processed with the simulator applying the proposed methodology: (<b>a</b>) recovered VTEC, (<b>b</b>) VTEC error with respect to the database VTEC.</p> "> Figure 9
<p>FRA vs. latitude of a pixel along the descending orbit: (<b>a</b>) database FRA (red) and retrieved simulated FRA (green), (<b>b</b>) error of the retrieved simulated FRA with respect to the database.</p> "> Figure 10
<p>VTEC of a descendent orbit over the Pacific Ocean, March 20th, 2014 obtained from SMOS radiometric data: (<b>a</b>) retrieved VTEC, (<b>b</b>) VTEC difference with respect to the database VTEC, (<b>c</b>) retrieved VTEC with the refined methodology (extension of alias free-field of view (AF-FoV) to the laterals), (<b>d</b>) difference of the retrieved VTEC with the refined methodology and the database VTEC.</p> "> Figure 11
<p>FRA vs. latitude of a pixel along the descending orbit: (<b>a</b>) database FRA (red) and retrieved FRA with SMOS radiometric data (green), and (<b>b</b>) retrieved FRA difference with respect to the database.</p> "> Figure 12
<p>Comparison of the VTEC coming from different sources.</p> "> Figure 13
<p>VTEC of all descending orbits on March 20th, 2011: (<b>a</b>) database VTEC, (<b>b</b>) retrieved VTEC using radiometric SMOS data with the proposed methodology, and (<b>c</b>) differences between the retrieved VTEC and the database VTEC with a RMSD of 17.84 total electron content units (TECU).</p> "> Figure 13 Cont.
<p>VTEC of all descending orbits on March 20th, 2011: (<b>a</b>) database VTEC, (<b>b</b>) retrieved VTEC using radiometric SMOS data with the proposed methodology, and (<b>c</b>) differences between the retrieved VTEC and the database VTEC with a RMSD of 17.84 total electron content units (TECU).</p> "> Figure 14
<p>Recovered VTEC of descending orbits over (<b>a</b>) the Bering Sea in March 21st, 2011, (<b>b</b>) the Bering Sea on March 20th, 2012, (<b>c</b>) the Barents Sea on March 21st, 2011, and (<b>d</b>) Barents Sea on March 22nd, 2019.</p> ">
Abstract
:1. Introduction
2. Data and Methods
2.1. Faraday Rotation
2.2. Data Sources
2.2.1. SMOS Brightness Temperatures
2.2.2. Geomagnetic Field and the Consolidated VTEC Databases
2.2.3. SMOS Level 2 VTEC (DTBXY Product)
2.2.4. GPS VTEC
2.3. FRA End-to-End Simulator
2.4. VTEC Retrieval from Radiometric Data
- Applying a temporal filter as a triangle filter with a window of 43 TB snapshots.
- Computing the FRA from the TB using Equation (3), rejecting pixels with incidence angles lower than 25° in order to avoid the indetermination in pixels with and .
- Computing the VTEC from the retrieved FRA using Equation (1), rejecting pixels with a threshold of to avoid the indetermination that emerges from that equation.
- Applying a spatial filter with a radius of 0.189 in the director cosine plane of VTEC snapshots.
- Generating VTEC maps in an ETOPO5 grid at 450 km of altitude.
2.5. Recovered VTEC Maps with Simulated Data
3. Results and Discussion
3.1. VTEC Retrievals from SMOS Data
3.2. Comparison of Retrieved VTEC from SMOS with Other External VTEC Sources
3.3. Impact of RFI Contamination in the Retrieved VTEC
4. Conclusions
Author Contributions
Funding
Conflicts of Interest
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Polarization | ||
---|---|---|
X | 76.8 | 203 |
Y | 95.5 | 206 |
Retrieval with | RMSD [TECU] |
---|---|
Simulated data | 0.48 |
Retrieval in the EAF-FoV | 15.69 |
Retrieval in AF-FoV and extension to the EAF-FoV | 10.81 |
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Rubino, R.; Duffo, N.; González-Gambau, V.; Corbella, I.; Torres, F.; Durán, I.; Martín-Neira, M. Deriving VTEC Maps from SMOS Radiometric Data. Remote Sens. 2020, 12, 1604. https://doi.org/10.3390/rs12101604
Rubino R, Duffo N, González-Gambau V, Corbella I, Torres F, Durán I, Martín-Neira M. Deriving VTEC Maps from SMOS Radiometric Data. Remote Sensing. 2020; 12(10):1604. https://doi.org/10.3390/rs12101604
Chicago/Turabian StyleRubino, Roselena, Nuria Duffo, Verónica González-Gambau, Ignasi Corbella, Francesc Torres, Israel Durán, and Manuel Martín-Neira. 2020. "Deriving VTEC Maps from SMOS Radiometric Data" Remote Sensing 12, no. 10: 1604. https://doi.org/10.3390/rs12101604