Active Microwave Physics and Basics

1. Active Microwave Physics and Basics Simon Yueh JPL, Pasadena, CA August 14, 2014

2. How Deep Can the Radio Waves Penetrate • 10 to17 GHz microwave can penetrate dry snowpack with a broad range of depth (1 to 5 m) 0.01m 0.1m 1m 10m • Experiment, Radio Laboratory, Helsinki University of Technology in 1987 • Theoretical simulations from bicontinuous medium/NMM3D, Xu et al, 2012

3. Radar Sounding of SnowSurface Scattering • Surface scattering dominates at near nadir looking • Early demonstration by late Prof. Hal Boyne (CSU) • Current Status – A well-developed tool for probing the snow stratigraphy • Marsahll et al., ground-based FMCW Radar • Gogineni et al., aircraft-based Snow Radar Courtesy of Boyne • What is the resolution? • ΔR=Range resolution=C/2B • ΔH=H(1/cosθ-1) for rough interface • Beamwidth(2θ) and height (H) • Horizontal resolution=2Hθ – limited by beamwidth ΔH ΔR

4. Off-nadir Looking RadarVolume Scattering SAR processing can achieve horizontal resolution of a few meters from space At off-nadir angles (30-50 degrees incidence angles) Volume scattering starts to dominate Surface scattering diminishes • Main parameters for snow backscatter: • Dry snow • Snow water equivalent • Grain size (d) • Density (ρ) • Soil background signal • Wet snow • Liquid water content (radar signal does not penetrate) Backscatter contributions: Volume, surface, and interaction terms. Observed backscatter coefficient σ° :

5. One example of data and theoryMore data acquired through CLPX2, SnowScat and SnowSAR campaigns • Snow SnowSCATbackscatter time series σvv with 40∘ incidence angle against SWE. Data taken from at Sodankylä between 12/28 /2010 and 03/01/2011. Simulated radar backscatter using the DMRT/QCA for snow volume scatteringat three frequencies. All three frequencies show response to snow water equivalent for moderate and large grain size.

6. SAR Snow TomographySide-looking radar with multiple baselines Measurements at Reynolds Creek study site, 200 meters from tower-116 manual probe depth measurements. (Marshall et al. of BSU) n Lel • Snow stratigraphy - Metamorphism and environmental factors create complex layering structures in the snow pack r dr • SAR Tomography • Tested for 3-D forest canopy mapping • Coherence and multiple baselines • Demosntrated by GB-SAR, K Morrison of Cranfield U. Height (m) • SAR Tomography will provide insight into snow and ice • Lack of comprehensive theoretical development and experimental testing for snow Slant Range (m) Polarimetrictomographic profile over a forested area using DLR’s E-SAR system at L-band [Moreira et al., IEEE GRS magazine, 2013].

7. Recent campaigns covering main snow regimes Inuvik, Canada, Tundra Sodankylä, Finland, Taiga Churchill, Canada, Tundra Colorado, USA Alpine/Tundra/ Taiga/Prairie Innsbruck, Austria, Alpine Kuparuk, Alaska, Tundra (Near-)Coincident Ku-band and X-band scatterometers and SAR used

8. Radar backscatter versus SWE – from Sodankylä, Finland, Taiga SnowScat measurements at 40° for two winters Backscatter versus observed SWE, Sodankylä, Finland , SnowScat measurements for winter I , for winter II  radiativetransfermodel calculation for 3 different values of grain size

9. Radar backscatter versus SWE – from Rocky Mountain, Colorado NASA/JPL POLSCAT measurements Backscatter for VV, HH, and VH polarizations shows sensitivity to SWE for three sampling sites Yueh et al., Airborne Ku-band Polarimetric Radar Remote Sensing of Terrestrial Snow Cover, IEEE TGRS, Vol. 47, No. 10, 3347-3364, 2009.