1. 08.04.10 GPS Multipath and its Relation to Near-Surface Reflectivity Slide 1/14 Natasha Whitney Harvard University National Geodetic Survey/NOS Mentor: Andria Bilich

2. 08.04.10 Forecast Slide 2/14 Can we use reflected GPS satellite signals (multipath errors) to detect nearby precipitation events and soil moisture content?

3. 08.04.10 Outline Slide 3/14 Background Methodology Results Further work Summary Acknowledgement

4. 08.04.10 Background Slide 4/14 Signal to noise ratio (SNR) Ground reflectivity & soil moisture content Geometric optics: (i)Specular reflection (ii)Ray tracing d  =2  2hcosθdθ dt dt

5. 08.04.10 Methodology Slide 5/14 Large metal experiment: Simplify various parameters Effective penetration depth (d) Polarization (all Left Hand Circular) Reflect signal amplitude attenuation

6. 08.04.10 Methodology Slide 5/14 Signal Amplitude (A) Antenna gain Effective reflector height (h) Phase center offset Governing equation SNR MP =A M cos(  +  o )

7. 08.04.10 Results Slide 7/14 Observations: -non-sinusoidal @ low  -noisy @ midrange  -suppressed at high  Relevant range of  ?

8. 08.04.10 Results Slide 6/14 Fast Fourier Transform (FFT): Eff. reflector height? Max amp? Wavelet Analysis: Phase center offset changes?

9. 08.04.10 Results Slide 8/14 Initial modeling attemptsRole of surface roughness

10. 08.04.10 Results Slide 9/14 Sensitivity of interference fringes to sea surface roughness for L2 signal Second modeling attempt

11. 08.04.10 Results Slide 10/14 Predicted Antenna Gain Experimental results: Effect of 180  rotation

12. 08.04.10 Results Slide 11/14 Antenna tilted 90  Effect of tilt on raw SNR signal

13. 08.04.10 Further Work Slide 12/14 1.Reduce edge effects: reduce discontinuity of induced electric field of conducting plane 2.Continue tomographical scan: use azimuthal, boresite, and tilt rotations to assess amplitude, phase center, and effective reflector height

14. 08.04.10 Summary Slide 13/14 Hypothesis v. Results: How useful was the large metal experiment? Calibration potential: Which parameters can provide real, physical information? Bigger picture: In-situ soil moisture network

15. 08.04.10 Acknowledgements Slide 14/14 Thank you NGS and ESRL team at Skaggs: Valery Zavorotny Felipe Nadinsky [TKTK] Kristine Larson Andria Bilich Kyle [TKTK] Resources used: VALERY PRES. 1.K. M. Larson, E. E Small, E. Gutmann, A. Bilich, J. Braun, and V. Zavorotny, “ Use of GPS receivers as a soil moisture network for water cycle studies, ” Geophys. Res. Lett. vol.. 35, no. DOI:10.1029/2008GL036013, p. L24405, 2008. 2.K. M. Larson, J. J. Braun, E. E. Small, V. U. Zavorotny, E. Gutmann, and A. L. Bilich, “ GPS multipath and its relation to near surface soil moisture content ﾓﾊ IEEE J. Sel. Topics Appl. Earth Obs. Remote Sens.” vol. 3 no. 1, Mar. 2010. 3.V. U. Zavorotny, K. M. Larson, J. J. Braun, E. E. Small, E. D. Gutmann, and A. L. Bilich, “ A Physical model for GPS Multipath Caused by Land Reflections: Toward Bare Soil Moisture Retrieval ”, IEEE ﾊ J. Sel. Topics Appl. Earth Obs. Remote Sens. Vol. 3, no. 1, Mar. 2010. 4.Bilich, A. L., "Improving the Precision and Accuracy of Geodetic GPS: Applications to Multipath and Seismology". Ph.D. dissertation, University of Colorado, 2006.

16. 08.04.10 Backup Slides Team survey topography at Table Mountain Experimental Site