Day 4

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Paper title Results of a Ground-based Coastal Campaign Targeting Sea Surface Doppler Measurements at X/Ku-band Using Signals of Opportunity
  1. Serni Ribó Institute of Space Sciences (ICE-CSIC, IEEC) Speaker
  2. Estel Cardellach Institute of Space Sciences (ICE-CSIC, IEEC)
  3. Weiqiang Li Institute of Space Sciences (ICE-CSIC, IEEC)
  4. Antonio Rius Institute of Space Sciences (ICE-CSIC, IEEC)
Form of presentation Poster
  • A8. Ocean
    • A8.10 Ocean Doppler: Challenges and Opportunities for Future Missions of Global Ocean Surface Currents
Abstract text Using signals of opportunity (SoOP), i.e. signals already transmitted for uses different from remote sensing, is an advantageous way to carry out bi-static observations at a reduced cost, as the transmitter is already operated for its primary use. Consolidated examples of this are GNSS Radio Occultation measurements [e.g., 1] and GNSS Reflectometry measurements [e.g., 2, 3] done from space.

Different research projects have been carried out during the last decade in order to use SoOP at higher frequencies e.g. [4, 5], and thus shorter wavelengths, to study the ocean surface. Parameters of interest are the sea surface roughness and sea surface altimetry. Candidate source of opportunity are FM-radio or digital satellite TV signals broadcasted from geostationary orbit. In particular, digital satellite TV signals have a very large potential thanks to i.) the large number of broadcasting satellites (~300), ii.) their extremely large total bandwidth which can span up to 2 GHz when many TV channels are considered, and iii.) the stronger available power compared to GNSS signals. This results in an expected precision of few cm in altimetric sea-surface observations [6].

In addition to these potentialities, when considering the larger available power, digital satellite TV signals can be used in bi-static geometries different from forward scattering. In these geometries, the Doppler signature of the reflected signals is also affected by the horizontal movement of the reflecting target. Thus, the horizontal velocity component of the ocean waves and the ocean current will affect the Doppler frequency of the reflected signal. In addition, as the wavelength of these signals is shorter (λ~2.5 cm) the Doppler frequency will have also a larger value compared to GNSS signals. An experimental demonstration of estimating the water velocity of a river using digital satellite TV signals can be found in [7].

In August 2021, an experimental campaign was carried out at the Majorca Island. On top of its highest peak (Puig Major 1480 m) two antennas were installed. The first one was used to acquire the direct TV signals transmitted from the ASTRA 1M (19.2E) satellite. The second antenna was pointed towards the sea to collect the signals that bounced off the sea surface, in non-specular but back- and side-scattering geometry. Direct and reflected signals were down-converted to IF, digitized at 80 Msps and stored on a SSD hard drive. Different data acquisitions were carried out in a variety of conditions: Signals of different TV channels were used, thus having diversity in wavelength. The down-looking antenna was also pointed at different elevation angles and azimuths with respect to the direction of the waves/currents.

The recorded data are being post processed. We will present preliminary results of the experimental campaign in order to try to establish the main aspects to be considered in a future airborne or space-borne instrument for a cost-effective direct measurement of the sea surface currents.

[1] Kursinski, E. R., Hajj, G. A., Schofield, J. T., Linfield, R. P., & Hardy, K. R. (1997). Observing Earth's atmosphere with radio occultation measurements using the Global Positioning System. Journal of Geophysical Research: Atmospheres, 102(D19), 23429-23465.

[2] Foti, G., Gommenginger, C., Jales, P., Unwin, M., Shaw, A., Robertson, C., & Rosello, J. (2015). Spaceborne GNSS reflectometry for ocean winds: First results from the UK TechDemoSat‐1 mission. Geophysical Research Letters, 42(13), 5435-5441

[3] Ruf, C. S., Atlas, R., Chang, P. S., Clarizia, M. P., Garrison, J. L., Gleason, S., ... & Zavorotny, V. U. (2016). New ocean winds satellite mission to probe hurricanes and tropical convection. Bulletin of the American Meteorological Society, 97(3), 385-395.

[4] Ribó, S., Arco, J. C., Oliveras, S., Cardellach, E., Rius, A., & Buck, C. (2014). Experimental results of an X-Band PARIS receiver using digital satellite TV opportunity signals scattered on the sea surface. IEEE Transactions on Geoscience and Remote Sensing, 52(9), 5704-5711.

[5] Shah, R., Garrison, J. L., & Grant, M. S. (2011). Demonstration of bistatic radar for ocean remote sensing using communication satellite signals. IEEE Geoscience and Remote Sensing Letters, 9(4), 619-623.

[6] Shah, R., Garrison, J., Ho, S. C., Mohammed, P. N., Piepmeier, J. R., Schoenwald, A., ... & Bradley, D. (2017, July). Ocean altimetry using wideband signals of opportunity. In 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS) (pp. 2690-2693). IEEE.

[7] Ribó, S., Cardellach, E., Fabra, F., Li, W., Moreno, V., & Rius, A. (2018, September). Detection and Measurement of Moving Targets Using X-band Digital Satellite TV Signals. In 2018 International Conference on Electromagnetics in Advanced Applications (ICEAA) (pp. 224-227). IEEE.