1. WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE § Remote Sensing Lab, Dept. TSC, Building D3, Universitat Politècnica de Catalunya, Barcelona, Spain and IEEC CRAE/UPC ∞ SMOS-Barcelona Expert Centre, Barcelona, Spain Tel. +34934054664, E-08034 Barcelona, Spain. E-mail: nereida@tsc.upc.edu N. Rodriguez-Alvarez §, X. Bosch-Lluis §, A. Camps §∞, I. Ramos-Perez §, E. Valencia §, H. Park §, M. Vall-llossera §∞ WE1.T06: Coastal and Wetlands III IGARSS’11 – Vancouver, Canada, 24 th -29 th July 2011

2. © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE 1.INTRODUCTION 2.THE SMIGOL REFLECTOMETER 3.FUNDAMENTALS OF THE INTERFERENCE PATTERN TECHNIQUE 4.FIELD EXPERIMENT 5.RESULTS 6.CONCLUSIONS 7.ACKNOWLEDGEMENTS INDEX (1/14)

3. Use of Global Navigation Satellite Signals Reflections (GNSS-R) techniques REMOTE SENSING OceanLand Ice Altimetry Sea State [1-5] Soil Moisture [6, 7] Vegetation height [7] Surface topography [7] Altimetry Age INTRODUCTION [4] E. Valencia, A. Camps, X. Bosch-Lluis, N. Rodriguez-Alvarez, I. Ramos-Perez, F. Eugenio and J. Marcello, "On the Use of GNSS-R Data to Correct L-Band Brightness Temperatures for Sea-State Effects: Results of the ALBATROSS Field Experiments", IEEE Transactions on Geoscience and Remote Sensing, Accepted June 2011. [7] Rodriguez-Alvarez, N., A. Camps, M. Vall-llossera, X. Bosch-Lluis, A. Monerris, et. al., (2011), Land geophysical parameters retrieval using the interference pattern GNSS-R technique, Geoscience and Remote Sensing, IEEE Transactions on, 49 (1), 71- 84, doi:10.1109/TGRS.2010.2049023. [6] Rodriguez-Alvarez, N., X. Bosch-Lluis, A. Camps, M. Vall-llossera, E. Valencia, J. Marchan-Hernandez, and I. Ramos-Perez (2009), Soil moisture retrieval using GNSS-R techniques: Experimental results over a bare soil field, Geoscience and Remote Sensing, IEEE Transactions on, 47 (11), 3616 {3624, doi: 10.1109/TGRS.2009.2030672. [1] J.F.Marchan-Hernandez, N. Rodríguez-Álvarez, A. Camps, X. Bosch-Lluis, and I. Ramos-Perez, “Correction of the Sea State Impact in the L-band Brightness Temperature by Means of Delay-Doppler Maps of Global Navigation Satellite Signals Reflected over the Sea Surface,” IEEE Transactions on Geoscience and Remote Sensing,, vol. 46, issue. 10, part 1, pp. 2914 - 2923, October 2007. (2/14) © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE Snow Snow thickness [8] [2] Valencia, E., Marchan-Hernandez, J.F., Camps, A., Rodriguez-Alvarez, N., Tarongi, J.M., et. al. “Experimental relationship between the sea brightness temperature and the GNSS-R Delay-Doppler Maps: preliminary results of the ALBATROSS field experiments, in: Proceedings of the IEEE International Geoscience and Remote Sensing Symposium 2009, vol. III. Cape Town, South Africa, pp. 741–744, 2009. [8] N. Rodriguez-Alvarez, A. Aguasca, E. Valencia, X. Bosch-Lluis, I. Ramos-Perez, H. Park, A. Camps, M. Vall-llossera, Snow Monitoring using GNSS-R techniques. Proceedings of the IGARSS11, Vancouver, Canada, July 2011. FR4.T05: GNSS Remote Sensing in Atmosphere, Ocean and Hydrology II [5] H. Park, E. Valencia, N. Rodriguez-Alvarez, X. Bosch-Lluis, I. Ramos-Perez, A. Camps, “A New Approach to Sea Surface Wind Retrieval from GNSS-R Measurements.” Proceedings of the IGARSS11, Vancouver, Canada, July 2011. O.2 Poster Session 2 [3] J. F. Marchan-Hernandez, E. Valencia, N. Rodriguez-Alvarez, I. Ramos-Perez, X. Bosch-Lluis, A. Camps, F. Eugenio, and J. Marcello, “Sea-state determination using GNSS-R data,” IEEE Geosci. Remote Sens. Lett., vol. 7, no. 4, pp. 621–625, Oct. 2010.

4. Based on he interference pattern of the GPS direct and reflected signals, after reflecting over the surface. Objective: GNSS-R Technique studied: The Interference Pattern Technique (IPT) Centimeter accuracy altimetry retrieval over a water reservoir (3/14) © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE INTRODUCTION

5. Work frequency = 1.57542 GHz (GPS L1) Measures the interference between direct and reflected signals during all the satellite passages. THE SMIGOL REFLECTOMETER The Soil Moisture Interference-pattern GNSS Observations at L-band (SMIGOL) Reflectometer is the instrument implementing the IPT. Figure 1. The SMIGOL Reflectometer architecture. elevation angle of GPS satellite changes (Fig. 2). Samples @ 1 s received interferometric power is function of the elevation angle (Fig. 3) Result Figure 2. The received power is function of the GPS satellite position Main architecture (Fig. 1) (4/14) Figure 2. The received power is function of the GPS satellite position Figure 3. Received interference power as a function of the elevation angle © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE

6. THE USE OF THE IPT FOR WATER LEVEL MONITORING Received interferometric power Where : Figure 4. The SMIGOL Reflectometer basic configuration FUNDAMENTALS OF THE INTERFERENCE PATTERN TECHNIQUE (5/14) © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE For water level retrieval it is necessary to study the effect of the variation of the h -parameter

7. (6/14) © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE FUNDAMENTALS OF THE INTERFERENCE PATTERN TECHNIQUE Figure 5. Received interference power: (a) assuming an instrument height (respect to water level) of 1 m and 3 m, and (b) zoom. (a) (b) An equivalent situation was previously studied in [6]: topography retrieval of the surface. As it was found there, when the instrument is closer to the surface, the frequency of the oscillations vs. the elevation angle is lower than when the instrument is at a higher height. This height automatically translates into water level monitoring. EFFECT OF h-PARAMETER VARIATION

8. (7/14) © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE FUNDAMENTALS OF THE INTERFERENCE PATTERN TECHNIQUE THE ALGORITHM FOR RETRIEVAL Splits the interference powers into moving windows in elevation angle containing one minimum and one maximum. Compute distance between minimum and maximum positions, Δθ elev. Theoretically compute the distance for different instruments heights. Selects the instrument height that minimizes the error respect to Δθ elev. Finally subtracting the initial height it is possible to monitor the variations of the water level.

9. FIELD EXPERIMENT (8/14) © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE Figure 6. The SMIGOL-Reflectometer location within the Palau reservoir Site: water reservoir located at Palau d’Anglesola, Lleida, Spain. Site coordinates 41°40'12.22"N, 0°52'31.02"E Size of the site 181m x 107 m No wind blowing in the area, surface nearly especular. THE MEASUREMENT SITE

10. (9/14) © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE Figure 7. SMIGOL-Reflectometer measuring at the water reservoir Figure 8. SMIGOL-Reflectometer field of view THE MEASUREMENTS Measurements on October 30th, 2010 (DoY 303). Ground-truth = 2.140 m measured water level. Measurements on December, 10th, 2010 (DoY 344). Ground-truth = 3.000 m. Ground-truth measured with a laser distance sensor DLR130K BOSCH by averaging 10 measurements (accuracy of 1.5 mm) with respect to the phase center of the instrument FIELD EXPERIMENT

11. (10/14) © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE FIELD EXPERIMENT Figure 8. The SMIGOL-Reflectometer measured powers and the simulated powers by applying the algorithm for (a) satellite 16 on DoY = 303 and (b) satellite 31 on DoY = 344. THE h-PARAMETER RETIEVAL The SMIGOL-Reflectometer measurements were processed and the algorithm to compute the equivalent instrument height was applied to the two days of measurements Local maxima and local minima of measured and retrieved powers are in the same elevation angles

12. RESULTS (11/14) © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE SATMean level retrieved σrmseΔh 162.133 m6 mm9 mm7 mm 322.127 m6 mm14 mm13mm SATMean level retrieved σrmseΔh 222.982 m67 mm88 mm18 mm 312.991 m9 mm13 mm9 mm RETRIEVAL RESULTS DoY 303. Ground-truth = 2.140 m DoY 344. Ground-truth = 3.000 m

13. Ground-truthSATMean level retrieved Δh 3.000 m 222.982 m18 mm 312.991 m9 mm 3.006 m 282.997 m9 mm 3.012 m 193.002 m10 mm 233.003 m9 mm 3.024 m 243.017 m7 mm 3.036 m 133.022 m14 mm 243.028 m8 mm 3.048 m 173.052 m5 mm 83.032 m16 mm 73.037 m11 mm RESULTS © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE Figure 9. The water level retrieved vs the ground-truth measured. ρ = 97%, with a Pe = 1.33·10-2 and R2 = 93%. SENSITIVITY STUDY (12/13)

14. CONCLUSIONS © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE The Interference Pattern Technique and the SMIGOL-Reflectometer have demonstrated to be extremely simple and yet powerful tools to monitor the water level in reservoirs and lakes. The algorithm developed is based on the instantaneous frequency of the oscillations of the detected interference power. Water level can be estimated with centimeter accuracy. (13/14)

15. This work by funds from the Plan Nacional del Espacio of the Spanish Ministry in the frame of the project with reference ESP2007-65567-C04-02 and also by funds from the project with reference AYA2008-05906-C02-01/ESP. ACKNOWLEDGEMENTS (14/14) © R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24 th -29 th July 2011 WATER LEVEL MONITORING USING THE INTERFERENCE PATTERN GNSS-R TECHNIQUE

16. THANK YOU