snow monitoring using gnss-r techniques § remote sensing lab, dept. tsc, building d3, universitat...

SNOW MONITORING USING GNSS-R TECHNIQUES

§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 protected]

N. Rodriguez-Alvarez§, A. Aguasca §, E. Valencia§, X. Bosch-Lluis§, I. Ramos-Perez§,

H. Park§ , A. Camps§∞, M. Vall-llossera§∞

IGARSS’11 – Vancouver, Canada, 24th -29th July 2011

FR4.T05: GNSS Remote Sensing in Atmosphere, Ocean and Hydrology II

© R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24th-29th July 2011

1. INTRODUCTION

2. THE SMIGOL REFLECTOMETER

3. FUNDAMENTALS OF THE INTERFERENCE PATTERN TECHNIQUE

4. FIELD EXPERIMENT

5. RESULTS

6. CONCLUSIONS

7. ACKNOWLEDGEMENTS

INDEX

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Use of Global Navigation Satellite Signals Reflections (GNSS-R) techniques

REMOTE SENSING

Ocean Land Ice

• Altimetry

• Sea State

• Soil Moisture

• Vegetation height

• Surface topography

• Altimetry

• Age

INTRODUCTION

(2/14)© R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24th-29th July 2011

Inland waters

• Reservoir Level


Snow

• Thickness

Based on he interference pattern of the GPS direct and reflected signals, after reflecting from the surface.

Objective:

GNSS-R Technique studied: The Interference Pattern Technique (IPT)

Snow thickness monitoring.


INTRODUCTION


0 20 40 60 80 100-50

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Elevation angle (º)

Rec

eive

d po

wer

(dB

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Reflectivity for snow covered soil (5 cm)

• Central 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 depends on the elevation angle (Fig. 3)

• Result

Figure 2. The received power is function of the GPS satellite position

• Main architecture (Fig. 1)

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Figure 2. The received power is function of the GPS satellite position

Figure 3. Received interference power as a function of the elevation angle



THE USE OF THE IPT FOR WATER LEVEL MONITORING

21, jeRGPower

cos hGPS

4

Received interferometric power

Where :

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22312

1

iS

iS

eerr

eerrR

Figure 4. The SMIGOL Reflectometer basic configuration

FUNDAMENTALS OF THE INTERFERENCE PATTERN TECHNIQUE

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irrt thn

2

22

12

22sincos

2

2128

irrS

sin





Figure 5. Received interference power assuming snow thickness layer of (a) 5 cm and (b) 40 cm. (a) (b)

• An equivalent situation was previously studied: vegetation height retrieval.

• As it was found there, when the snow thickness increases the number of notches and change their position.

EFFECT OF THE SNOW THICKNESS


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d po

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NOTCH NOTCHES



THE ALGORITHM FOR RETRIEVAL• From theory the notches evolution dependence on the elevation angles is found, fig. 6.


•For the first DoY of measurement, select the notches in the received powers sequences and compute the snow thickness based on fig. 6. • In order to solve the uncertainly, assume that 5 cm is the snow thickness (known from ground-truth), and choose the nearest solution.• The solution for each satellite is stored for being used as the calibration measurement.• From that measurement the evolution of notches is tracked. The criterion to solve the uncertainty, when processing the following measurement days, has been stated to be that snow falling affects all the surface in the same way and then the most probable solution obtained from fig. 6 is selected.

Figure 6. Theoretical evolution of notches. The notches position and the number of them (each black line defines the evolution of one notch) describe the snow thickness. The snow layer has been simulated considering a snow wetness volume of 2% and a snow density of 8 %.

FIELD EXPERIMENT


Figure 7. The measurements site, Pla de Beret, Vall d’Aran, Lleida, Spain (42º42’44’’N, 0º56’22’’E)

THE MEASUREMENT SITE


• Site: Meteorological station located at Pla de Beret, Vall d’Aran, Lleida, Spain.

• Site coordinates 42º42’44’’N, 0º56’22’’E

• Collaboration: -Institut Geològic de Catalunya, Barcelona, Spain -Conselh Generau d’Aran, located at Vielha, Val d’Aran, Lleida, Spain


Figure 9. SMIGOL-Reflectometer measuring snow thickness Figure 10. SMIGOL-Reflectometer field of view

• Field experiment lasted 6 months from: November, 5th , 2010 to May, 25th, 2011

• SMIGOL-Reflectometer is an autonomous instrument powered by solar panels and batteries

• Ground-truth measured using an ultrasonic sensor, attached at a meteorological station mast.

FIELD EXPERIMENTSNOW MONITORING USING GNSS-R TECHNIQUES

Figure 8. Ground-truth for half of the field experiment.

THE MEASUREMENTS


FIELD EXPERIMENT

Figure 11. 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 PROCESSING

• The SMIGOL-Reflectometer measurements were processed and the algorithm to compute the equivalent snow thickness was applied to the measurements.

• Notches were selected and their position was analyzed, following fig. 6 and the criterion stated in the algorithm.


RESULTS


SNOW THICKNESS MAPS RETRIEVED


RESULTS

© R.S. Lab, UPC 2011. IGARSS 2011, Vancouver, Canada, 24th-29th July 2011 (12/13)


RETRIEVAL RESULTS. Correlation of the retrievals with the ground-truth snow thickness

CONCLUSIONS


• The Interference Pattern Technique and the SMIGOL-Reflectometer are able to monitor the snow thickness variations.

• The retrieval algorithm developed is based on the position of notches, plus a tracking function that daily analyzes the movement of that notches in the received power plots.

• The correlation values of the measurements with the ground-truth in different points of the surface show that the technique can monitor changes in the snow thickness.

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This work has been sponsored with 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 and the project AYA2010-22062-C05-05/ESP.

ACKNOWLEDGEMENTS



THANK YOU

snow monitoring using gnss-r techniques § remote sensing lab, dept. tsc, building d3, universitat...

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