The document describes using GNSS reflectometry to monitor water levels in a reservoir with centimeter accuracy. It details using the interference pattern technique with the SMIGOL reflectometer to measure the interference between direct and reflected GPS signals. By analyzing how the interference pattern changes with satellite elevation angle and water level, the technique can estimate water level to within centimeters compared to ground measurements. Field tests at a reservoir achieved this level of accuracy.

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: [email_address] 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

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

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

13. 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) Ground-truth SAT Mean level retrieved Δh 3.000 m 22 2.982 m 18 mm 31 2.991 m 9 mm 3.006 m 28 2.997 m 9 mm 3.012 m 19 3.002 m 10 mm 23 3.003 m 9 mm 3.024 m 24 3.017 m 7 mm 3.036 m 13 3.022 m 14 mm 24 3.028 m 8 mm 3.048 m 17 3.052 m 5 mm 8 3.032 m 16 mm 7 3.037 m 11 mm

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

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