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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
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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 • Processing / Calibration • Example radar profiles / snow pit data • Comparison with in-situ electrical measurements • Preliminary modeling results • 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)
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 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?