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

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

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))

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

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)

Berthud Pass, February 22, 2003

Michigan Ridge, North Park, Feb 21,2003

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

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

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

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)

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

Density profile vs radar

In-Situ Dielectric Properties

Dielectric properties vs integrated psd

Model results with unsmoothed, original data

Density profile calculated from modeled dielectric properties

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?