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Ground-Based FMCW radar during IOP3,4 H.P. Marshall, Institute of Arctic and Alpine Research, Univ. of Colorado Gary Koh, Cold Regions Research and Engineering Lab, New Hampshire Rick Forster, Department of Geography, University of Utah

Ground-Based FMCW radar during IOP3,4

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Ground-Based FMCW radar during IOP3,4. H.P. Marshall, Institute of Arctic and Alpine Research, Univ. of Colorado Gary Koh, Cold Regions Research and Engineering Lab, New Hampshire Rick Forster, Department of Geography, University of Utah. Outline. Brief Overview of FMCW theory - PowerPoint PPT Presentation

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Page 1: Ground-Based FMCW radar during IOP3,4

Ground-Based FMCW radar during IOP3,4H.P. Marshall, Institute of Arctic and Alpine Research, Univ. of Colorado

Gary Koh, Cold Regions Research and Engineering Lab, New Hampshire

Rick Forster, Department of Geography, University of Utah

Page 2: Ground-Based FMCW radar during IOP3,4

Outline

1.Brief Overview of FMCW theory

2.Processing / Calibration

3.Example radar profiles / snow pit data

4.Comparison with in-situ electrical measurements

5.Preliminary modeling results

6.Conclusions / Future Work

Page 3: Ground-Based FMCW radar during IOP3,4

FMCW Theory

• Linear frequency chirp transmitted (T)

• Received signal (R) “mixed” with transmitted wave before signal acquisition

• Recorded signal contains the sum and difference frequencies from T + R

• Frequency differences from reflectors linearly related to the distance to target

• T=dF*pl/*BW• D=T*c/(2*sqrt(e))

Page 4: Ground-Based FMCW radar during IOP3,4

Signal Processing

• Vertical resolution of signal ~ (pl Fs)/(BW*N)• High-resolution FFT – N > number of samples• Zero-padding, Welch window, no overlap

wi=1-((n-N/2)/(N/2))^2• Optimal (Wiener) Filtering did not improve images

Page 5: Ground-Based FMCW radar during IOP3,4

Calibration

• Metal reflectors placed at known depths

• Accurate depth scale, will also be used to calculate attenuation

• Each trace normalized by integrated psd from horn to snow surface

• Each scan normalized by integrated psd from known reflector on surface (shovel handle)

Page 6: Ground-Based FMCW radar during IOP3,4

Berthud Pass, February 22, 2003

Page 7: Ground-Based FMCW radar during IOP3,4

Michigan Ridge, North Park, Feb 21,2003

Page 8: Ground-Based FMCW radar during IOP3,4

LSOS March 25, 2003, Ku-Band (14-18 GHz)

Page 9: Ground-Based FMCW radar during IOP3,4

LSOS March 25, 2003, X-Band (8-12 GHz)

Page 10: Ground-Based FMCW radar during IOP3,4

LSOS March 25, 2003 – C-Band (2-6 GHz)

Page 11: Ground-Based FMCW radar during IOP3,4

Quantitatively Relating FMCW signal to physical properties

• FMCW => in-situ dielectric properties (Finish snowfork)

• In-situ properties => physical properties

(e.g. Sihvola et al, 1985)

Page 12: Ground-Based FMCW radar during IOP3,4

Relationship of FMCW signal to in-situ electrical and manual measurements

Page 13: Ground-Based FMCW radar during IOP3,4

Density profile vs radar

Page 14: Ground-Based FMCW radar during IOP3,4

In-Situ Dielectric Properties

Page 15: Ground-Based FMCW radar during IOP3,4

Dielectric properties vs integrated psd

Page 16: Ground-Based FMCW radar during IOP3,4

Model results with unsmoothed, original data

Page 17: Ground-Based FMCW radar during IOP3,4

Density profile calculated from modeled dielectric properties

Page 18: Ground-Based FMCW radar during IOP3,4

Conclusions / Future Work

• Find best model for wide range of snowpack types• Use results to update depth scale with multi-layer

model• find optimal response function which relates broad

band FMCW signal to narrowband airborne signals• Adapt for different frequency ranges, bandwidths, look

angles• Suggestions?