The Multifrequency Future for Remote Sensing of Sea Surface Salinity from Space
<p>Frequency and bandwidth used by passive microwave sensors in space. The solid circles indicate the primary frequency (best sensitivity to the identified parameter desired) and the open circles indicate other frequencies employed in the retrieval algorithms to help correct for competing effects on observed emissivity.</p> "> Figure 2
<p>Brightness temperature as a function of SST for constant SSS. The calculations are for a flat surface (no wind), a frequency of 1.413 GHz and at nadir (zero incidence angle). The calculations use the Klein-Swift dielectric constant model function [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>].</p> "> Figure 3
<p>Brightness temperature as a function of SST for constant SSS. The calculations are for a flat surface (no wind) with a frequency of 1.413 GHz and 40° incidence angle. Horizontal polarization (<b>a</b>); Vertical polarization (<b>b</b>). The calculations use the Klein-Swift dielectric constant model function [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>].</p> "> Figure 4
<p>Sensitivity of brightness temperature, TB, to changes in salinity, SSS, as a function of frequency: (<b>a</b>) dependence on incidence angle (SST = 20 °C; SSS = 35 psu); (<b>b</b>) dependence on SST at 40° incidence angle (SSS = 35 psu). These results are for a flat surface (no roughness) and use the Klein-Swift [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>] model function for the dielectric constant of sea water. Above 5 GHz, the curves continue the reported trend and converge to 0.</p> "> Figure 5
<p>(<b>a</b>) Sensitivity of change in brightness temperature to a change in salinity, dTB/dSSS, as a function of salinity for several temperatures. This curve is for 1.413 GHz at normal incidence and no roughness. Based on the Klein-Swift [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>] model function; (<b>b</b>) Histogram of number of samples for each salinity reported by Argo floats near Aquarius footprints for the period 2011–2015.</p> "> Figure 6
<p>Sensitivity of brightness temperature to changes in temperature, SST, as a function of frequency for SSS = 35 psu and SST = 25 °C. Dashed line at nadir and solid line at 40° incidence angle. These figures are for a flat surface and use the Klein-Swift [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>] model function. (<b>b</b>) is the same as (<b>a</b>) with expanded frequency scale to show the behavior at low frequency.</p> "> Figure 7
<p>Sensitivity of brightness temperature to changes in temperature, SST, as a function of frequency for selected temperature, at nadir. These curves are for SSS = 35 psu, a flat surface, and use the Klein-Swift [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>] model function. (<b>b</b>) is the same as (<b>a</b>) but with expanded frequency scale to show detail below 20 GHz.</p> "> Figure 8
<p>Level curves of TB vs. SST for constant wind speed, WS. The WS increases in steps of 2 m/s starting as zero at the bottom and increasing to 18 m/s at the top. These curves are for nadir (zero incidence angle) and SSS = 35 psu: (<b>a</b>) 1.4 GHz; (<b>b</b>) 6.8 GHz; (<b>c</b>) 18.7 GHz; (<b>d</b>) 37.0 GHz.</p> "> Figure 9
<p>Brightness temperature as a function of frequency: (<b>a</b>) At nadir and several values of SST; (<b>b</b>) SST = 20 °C for nadir and 40° incidence angle. All curves are for SSS = 35 psu, zero wind speed (flat surface) and use the Klein-Swift model function [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>] for the dielectric constant of sea water.</p> "> Figure 10
<p>Brightness temperature vs. SST for constant wind speed at: (<b>a</b>) 1.4 GHz; (<b>b</b>) 6.8 GHz; (<b>c</b>) 18.7 GHz. The dashed curves are for 0 m/s. Black dashed is at nadir, red is vertical polarization and blue is horizontal polarization at 40° incidence angle. The solid curves are for WS = 7 and 14 m/s.</p> "> Figure 11
<p>Sensitivity, dTB/dWS, of brightness temperature to a change in wind speed for incidence angles of 20<sup>o</sup> and 40° and SST = 20 °C; SSS = 35 psu: (<b>a</b>) 1.4 GHz; (<b>b</b>) 6.8 GHz; (<b>c</b>) 18.7 GHz.</p> "> Figure 12
<p>Sensitivity of brightness temperature to wind speed, dTB/dWS, as a function of frequency: Incidence angle = 40°; WS = 7 m/s; SST = 20 °C; SSS = 35 psu.</p> "> Figure 13
<p>Sensitivity of brightness temperature to WS (blue), SST (red) and SSS (black) for 40° incidence, WS = 7 m/s, SSS = 35 psu and SST = 20 °C. The figures also indicate attenuation due to the atmosphere (dashed line). For attenuation, the vertical axis is attenuation in dB per km at nadir. (<b>a</b>) Horizontal polarization; (<b>b</b>) Vertical polarization.</p> "> Figure 14
<p>Expanded view of sensitivities shown in <a href="#remotesensing-12-01381-f013" class="html-fig">Figure 13</a> with more frequency resolution in the range relevant to remove sensing of SSS: (<b>a</b>) Horizontal polarization; (<b>b</b>) Vertical polarization. The arrow indicates 1.4 GHz.</p> "> Figure A1
<p>Comparison of the brightness temperature as a function of frequency for three model functions for the dielectric constant of sea water: KS = Klein-Swift [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>]; MW = Meissner-Wentz [<a href="#B34-remotesensing-12-01381" class="html-bibr">34</a>]; GW = Zhou et al. [<a href="#B35-remotesensing-12-01381" class="html-bibr">35</a>]. The two figures are the same with expanded scale on the left to show details near 1.4 GHz where salinity is currently measured.</p> "> Figure A2
<p>Comparison of the sensitivity, dTB/dSSS, computed with the three model functions for the dielectric constant of sea water: KS = Klein-Swift [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>]; MW = Meissner-Wentz [<a href="#B34-remotesensing-12-01381" class="html-bibr">34</a>]; GW = Zhou et al. [<a href="#B35-remotesensing-12-01381" class="html-bibr">35</a>]. These examples are for SST = 25 °C and SSS = 35 psu and no wind (flat surface).</p> "> Figure A3
<p>Dependence on salinity of the sensitivity of brightness temperature to changes in temperature, dTB/dSST, for salinity found in the open ocean. This example is for nadir, SST = 25 °C and a flat surface (WS = 0 m/s) using the Klein-Swift model function [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>]. Top curve: 30 psu; middle curve (dashed): 33 psu; bottom curve: 36 psu.</p> "> Figure A4
<p>Dependence on salinity of the sensitivity of brightness temperature to changes in salinity, dTB/dSSS, as a function of frequency. The examples are for nadir, SST = 25 °C and WS = 0 m/s and made using the Klein-Swift model function [<a href="#B19-remotesensing-12-01381" class="html-bibr">19</a>].</p> "> Figure A5
<p>Specific attenuation at the surface for a standard atmosphere with Ts = 20 °C and RH20 = 60%. Computations using the MPM92 model [<a href="#B37-remotesensing-12-01381" class="html-bibr">37</a>,<a href="#B38-remotesensing-12-01381" class="html-bibr">38</a>,<a href="#B39-remotesensing-12-01381" class="html-bibr">39</a>]. (<b>b</b>) is the same as (<b>a</b>) but with expanded frequency scale.</p> ">
Abstract
:1. Introduction
1.1. Passive Microwave Remote Sensing Frequencies
1.2. Remote Sensing of Sea Surface Salinity
2. Methods
3. Results
3.1. Sensitivity of Brightness Temperature (TB) to Changes in Salinity: dTB/dSSS
3.1.1. Background
3.1.2. Dependence of Sensitivity, dTB/dSSS, on Temperature
3.1.3. Dependence of dTB/dSSS on Salinity
3.2. Sensitivity of TB to Changes in Temperature: dTB/dSST
3.3. Sensitivity of TB to Wind Speed (WS): dTB/dWS
3.3.1. Background
3.3.2. Dependence of TB on WS
3.3.3. Sensitivity of TB to Changes in WS: dTB/dWS
3.3.4. Frequency Dependence of Sensitivity: dTB/dWS
4. Discussion
5. Conclusions
Author Contributions
Funding
Conflicts of Interest
Appendix A. Model Functions for the Dielectric Constant of Sea Water
Appendix B. Dependence on Salinity
Appendix B.1. dTB/dSST
Appendix B.2. dTB/dSSS
Appendix C. Atmospheric Attenuation
Appendix D. Spectrum Management
Frequency GHz | Bandwidth MHz | Threshold | Not to Exceed % Time | Protection | |
---|---|---|---|---|---|
Power(dBW) | ΔTB(K) | ||||
1.4–1.427 | 27 | −174 | 0.05 | 0.1 | Protected |
6.425–7.25 | 200 | −166 | 0.05 | 0.1 | None |
10.68–0.70 | 100 | −166 | 0.10 | 0.1 | Protected |
18.60–18.80 | 200 | −163 | 0.10 | 0.1 | Shared |
23.60–24.00 | 200 | −166 | 0.05 | 0.01 | Protected |
36.00–37.00 | 100 | −166 | 0.10 | 0.1 | Shared |
52.60–59.30 | 100 | −169 | 0.05 | 0.01 | Protected |
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Le Vine, D.M.; Dinnat, E.P. The Multifrequency Future for Remote Sensing of Sea Surface Salinity from Space. Remote Sens. 2020, 12, 1381. https://doi.org/10.3390/rs12091381
Le Vine DM, Dinnat EP. The Multifrequency Future for Remote Sensing of Sea Surface Salinity from Space. Remote Sensing. 2020; 12(9):1381. https://doi.org/10.3390/rs12091381
Chicago/Turabian StyleLe Vine, David M., and Emmanuel P. Dinnat. 2020. "The Multifrequency Future for Remote Sensing of Sea Surface Salinity from Space" Remote Sensing 12, no. 9: 1381. https://doi.org/10.3390/rs12091381