Meetings: Documents

Latest L-band Seawater Dielectric Measurements
[27-Aug-18] Zhou, Y., Lang, R., Dinnat, E., and Le Vine, D.M.
Presented at the 2018 Ocean Salinity Science Team and Salinity Continuity Processing Meeting
A transmission-type TM mode resonant cavity has been employed to determine the seawater dielectric constant at L-band accurately (Lang et al. 2016). Based on the dielectric constant data, a dielectric model function has been generated and applied to retrieve the seawater surface salinity from the Aquarius satellite data (Zhou et al. 2017). The comparison between the retrieved salinity and the in situ data, however, indicated that more accuracy is still needed, especially at low temperature, for the dielectric measurements of seawater.
The experimental system has been upgraded recently in preparation for the low temperature measurements. The coaxial RF probes have been replaced with new ones that are TiN coated to prevent corrosion in the coolant. Thermistors with 0.01°C accuracy have been purchased and installed. The accuracy of the new thermistors has been validated throughout an extensive temperature range from -3°C to 35°C, which has improved the seawater dielectric measurements at low temperature. A new computer program has been developed to use a least-square fit to determine the resonant frequency and cavity Q from the raw data collected from the Network Analyzer instead of using the less accurate approximations outputted by the Network Analyzer itself. With all these upgrades, low temperature measurements have been made from -2°C to 2°C with 1°C step. Since most open ocean salinity values occur close to salinities of 35 psu, new measurements are being made at 34 and 36 psu to enhance the data set coverage for values near 35 psu. All the new data will be used to adjust the model function to improve its accuracy.
In the future, GW will investigate the design of a resonant cavity to measure the dielectric constant of seawater at P-band frequencies. The use of higher order cavities modes will also be examined to obtain dielectric constant measurements at higher frequencies with existing cavities.
References
Zhou, Y., R. Lang, E. Dinnat and D. Le Vine (2017). L-band model function of the dielectric constant of seawater, IEEE Transactions on Geoscience and Remote Sensing, 55(12), doi: 10.1109/TGRS.2017.2737419.
Lang, R., Y. Zhou, C. Utku, and D. Le Vine (2016). Accurate measurements of the dielectric constant of seawater at L-band, Radio Science, 51, 2-24, doi: 10.1002/ 2015RS005776.

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