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UltraWideband Radars (FM-CW) for Snow Thickness Measurements. Outline. Introduction Typical FM-CW Radar Background FM-CW radars design considerations Results Sea ice Land Future Conclusions . Basic FMCW Concept and some issues. f. Transmit Receive Mixed (Beat Freq ). k. - PowerPoint PPT Presentation
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UltraWideband Radars (FM-CW) for Snow Thickness Measurements
Outline• Introduction • Typical FM-CW Radar• Background• FM-CW radars design
considerations• Results
– Sea ice – Land
• Future• Conclusions
Basic FMCW Conceptand some issues
TransmitReceiveMixed (Beat Freq)
t
f
fB=kτ
• Mixing the tx and rx signals produces single tone cw signals.• FFT transforms into target delay.• Transmitting and receiving at the same time.• Transform has sidelobes (windowing and amplitude variations).
• Linear Chirp Considerations: for slow chirps and close targets, chirp non-linearities are near coincidental in tx and rx and tend to cancel.
k
FFT
Basic FM-CW Conceptand difficulties with airborne applcations
t
f
t
f
• Airborne applications require fast chirps and far targets.• Even slight non-linearities can cause major degradations.• Loss in resolution and FFT sidelobes.
Longer range Fast chirp to sample
Doppler (High PRF) and avoid target de-correlation.
• Ultra-Wideband >500 MHz
• FM-CW – Easy to implement– Low-sampling– Low power
• Disadvantages– Linearity– RX/TX Isolation– Sidelobes
• Application of FM-CW radars for snow studies started in 1970s– Used linearized VCOs– YIG oscillators
• Surface-based systems• Interfaces mapping was
demonstrated• A number of systems
have been built and used
FM-CW Radar
• We started our work in 2000 – Small grant from NASA
to develop a system– Collaboration with
Thurston Markus, GSFC
• Instruments being used on aircraft– Long-range– Short-range
2-18 GHz
Fast chirp problems
Surface-based
Airborne, 2006
Background
• Solved chirp problems in 2008• Fast-settling PLL + ultrawideband VCO
10 m
Ice Sheet Surface
Internal Accumulation
Layers
Snow Surface Air-Snow Boundary
Ice Surface Snow-Ice Boundary
1 m
Background
1. Antenna FeedthroughTwo antennas
2. Fast ChirpFast PLL +VCODDS + Multiplier
3. LO feedthrough High isolation amp4. Multiple reflections
Minimize cables and connectors
Typical FM-CW Radar
Instrument Measurements Frequency/Wavelength/ Bandwidth
Power Antenna Aircraft
MCoRDS/I Ice ThicknessInternal LayeringImage Bed Properties
195 MHz, 1.5 m 30 MHz/80 MHz
800 W Dipole ArrayWing -MountedFuselage
DC-8P-3Twin-Otter
Ku-BandAltimeter
Surface TopographyNear Surface Layering
15 GHz2 cm6 GHz
200 mW HornsBomb Bay
DC-8P-3Twin-Otter
Snow Radar Snow on Sea IceSurface TopographyNear Surface Layering
5 GHz7.5 cm6 GHz
200 mW Horns DC-8P-3
Accumulation Internal LayeringIce Thickness
750 MHz40 cm300 MHz
10 W Dipole ArrayVivaldi ArrayBomb Bay
P-3Twin-Otter
Radar Instrumentation
MCoRDS, Accumulation, Snow, and Ku-band radars
DC-8 and P-3B Antenna Configurations
Results – Arctic and Antarctic
Results – Snow and Ku-band Radar Comparison
Results – Greenland 2011
10 m
0.9 kmSnow Radar Ku-band Radar
10 m
0.9 km
• Extend frequency range– 2-18 GHz– 1-17 GHz
• Quad polarization• Digital beamforming
– 16-32 receivers– Measure backscatter as
function of incidence angle
• Backscatter data at number frequencies
• Invert data to estimate snow density and particle size
• Combine these with sounder-mode data to determine snow thickness
Future
Instrument Measurements Frequency range / Bandwidth
Power Antenna Aircraft
MCoRDS/I Ice thicknessInternal layeringImage bed properties
140-600 MHz460 MHz
800 W or ~2 kW
Slotted-ArrayWing -MountedFuselage
BaslerOther aircraft??
Ultra wideband microwave radar
Surface topographyNear-surface layeringSnow on sea iceSnow on land
2-18 GHz16 GHz
200 mW Vivaldi array DC-8P-3Twin-OtterBasler
Temperate ice Sounder
Ice thickness and layers
14 and 30 MHz 10 W Short Dipole Basler
Sea Ice Sounder
Ice thickness 50-300 MHz 10 W Broadband slot array
Twin Otter Basler
Future: Radar Instrumentation
2D infinite dual-pol array simulation
Ideal 8-element array patterns at 5, 10 and 15 GHz
Array Performance
• Advances in RF and Digital technologies enabled us:– To develop low-power and high sensitivity
ultrawideband radars– Wide use over sea ice– FCC permit to operate over land
Conclusions