The influence of spatial variability of polar firn on microwave emission Martin Proksch 1, Henning Löwe 1, Stefanie Weissbach 2, Martin Schneebeli 1 1 WSL-Institute for Snow- und Avalanche Research SLF, Davos, CH 2 Alfred-Wegener-Institute for Polar and Marine Research, Germany Microsnow Reading, 6. – 8. August 2014

Outline 1.Motivation 2.Instrument and measurements 3.Simulations and Results –Spatial variability –Layer thickness 4.Conclusions WSL-Institut für Schnee- und Lawinenforschung SLF2

1.Motivation 1.Motivation I Microwave observations are essential in polar regions (think about polar night!) To understand the microwave signatures of polar firn, in-situ data is necessary, but traditional snow measurements are: –limited in spatial resolution –limited by extensive measurement times –constrained due to harsh polar environments –subjective (variability between observers) Desirable: fast derivation of the relevant objective parameters with sufficient resolution (e.g. Correlation length and density to model microwave emission) WSL-Institut für Schnee- und Lawinenforschung SLF3

1.Motivation 1.Motivation II Where to measure (Sampling design)? Answer requires knowledge about snow variability! Pic: Martin Schneebeli 4WSL-Institut für Schnee- und Lawinenforschung SLF

2.1Instrument: SnowMicroPen (SMP)  Specifications:  High resolution: vertical ~1mm  Fast: 1 m profile ~ 1 minute –Portable => Ideal for spatial variability  Output: –Density, SSA and Correlation length (Proksch et al, submitted) –2D stratigraphy from transects 5

2.1Instrument: SnowMicroPen (SMP) 6 Density: Correlation length:

2.2Measurements at Kohnen Station: Density WSL-Institut für Schnee- und Lawinenforschung SLF7 92 SMP profiles with interval 0.5 m -> 45m transect:

2.2Measurements at Kohnen Station: Density WSL-Institut für Schnee- und Lawinenforschung SLF8 92 SMP profiles with interval 0.5 m -> 45m transect:

2.2Measurements at Kohnen Station: Correlation length l ex WSL-Institut für Schnee- und Lawinenforschung SLF9 92 SMP profiles with interval 0.5 m -> 45m transect:

2.2Measurements at Kohnen Station: specific surface area SSA WSL-Institut für Schnee- und Lawinenforschung SLF10 92 SMP profiles with interval 0.5 m -> 45m transect:

3.1MEMLS simulations WSL-Institut für Schnee- und Lawinenforschung SLF11 MEMLS: Microwave Emission Model of Layered Snowpacks, Wiesmann and Mätzler, > with Improved Born Approximation, Mätzler MEMLS input: 1cm layer thickness in top most meter l ex : SMP (no «grain size» scaling) Density: SMP Snow temperature profile T sky : 0K Snow-ground reflectivity: 0 20m deep profile, linearly increasing

3.2Results: Brightness temperatures WSL-Institut für Schnee- und Lawinenforschung SLF12 σ T b TbTb

3.2Results: Brightness temperatures WSL-Institut für Schnee- und Lawinenforschung SLF13 σ T b TbTb

3.2Results: Brightness temperatures WSL-Institut für Schnee- und Lawinenforschung SLF14  One MEMLS run per SMP profile, total N = 92  σ(T b, 36GHz ) = 16.6 K WSL-Institut für Schnee- und Lawinenforschung SLF14 σ T b TbTb

3.2Results: Brightness temperatures  One MEMLS run per SMP profile, total N = 92  σ(T b, 36GHz ) = 16.6 K To decrease σ, we have to increase the number of measurements N: σ(T b ) = 16 K for N=92 σ(T b ) = 8 K for N = 368 σ(Tb) = 2 K for N = 2944 WSL-Institut für Schnee- und Lawinenforschung SLF15 σ T b TbTb

3.2Results: Kohnen 16 Standard deviations: T 19GHz, V-pol = 7.1 K T 36GHz, V-pol = 16.6 K T 89GHz, V-pol = 17.2 K Constant Density:Constant corr. length T 19GHz, V-pol = 7.5 K T 19GHz, V-pol = 2.5 K T 36GHz, V-pol = 17.9 KT 36GHz, V-pol = 6.6 K T 89GHz, V-pol = 18.9 KT 89GHz, V-pol = 9.1 K

3.2Results: Summit 17 Standard deviations: T 19GHz, V-pol = 13.9 K T 36GHz, V-pol = 24.1 K T 89GHz, V-pol = 23.5 K Constant Density:Constant corr. length T 19GHz, V-pol = 13.5 K T 19GHz, V-pol = 3.7 K T 36GHz, V-pol = 26.1 KT 36GHz, V-pol = 3.8 K T 89GHz, V-pol = 27.8 KT 89GHz, V-pol = 7.0 K

3.2Results: Point Barnola WSL-Institut für Schnee- und Lawinenforschung SLF18 Standard deviations: T 19GHz, V-pol = 3.3 K T 36GHz, V-pol = 11.0 K T 89GHz, V-pol = 21.2 K Constant Density:Constant corr. length T 19GHz, V-pol = 4.5 K T 19GHz, V-pol = 1.2 K T 36GHz, V-pol = 12.8 KT 36GHz, V-pol = 1.5 K T 89GHz, V-pol = 23.7 KT 89GHz, V-pol = 4.3 K

3.3Results: Spatial correlations WSL-Institut für Schnee- und Lawinenforschung SLF19

3.3Results: Spatial correlations WSL-Institut für Schnee- und Lawinenforschung SLF20

3.3Results: Spatial correlations WSL-Institut für Schnee- und Lawinenforschung SLF21

3.3Results: Spatial correlations WSL-Institut für Schnee- und Lawinenforschung SLF22

3.3Results: Spatial correlations WSL-Institut für Schnee- und Lawinenforschung SLF23

3.3Results: Spatial correlations WSL-Institut für Schnee- und Lawinenforschung SLF24

3.3Results: Spatial correlations WSL-Institut für Schnee- und Lawinenforschung SLF25

3.4Results: Layer thickness WSL-Institut für Schnee- und Lawinenforschung SLF26 20m deep profile: –First meter SMP measurement –2 – 20 meter: linear increasing, with random noise added. 3 cm 20 cm

3.4Results: Effect of vertical averaging WSL-Institut für Schnee- und Lawinenforschung SLF27 Averaging to 3cm layer thickness leads to significant loss of density variations!

4.Summary and Conclusions WSL-Institut für Schnee- und Lawinenforschung SLF28  One single profile is not enough – statistically based sampling design?  Layer thickness critical The SnowMicroPen allows the measurement of full-meter profiles in less than one minute Transects reveals the 2D quantitative stratigraphy of polar firn o Outlook: optimize deep profiles to match Satellite data

s WSL-Institut für Schnee- und Lawinenforschung SLF29 Thank you! Thanks to: Christian Mätzler Ludovic Brucker

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3.5Results: Measurement accuracy WSL-Institut für Schnee- und Lawinenforschung SLF32 Meas. accuracy in top most meter To model Tb within 1K

Outlook Compare to SSMI WSL Institute for Snow and Avalanche Research SLF33

To do: Spat var - for other stations Layer thickness Meas accuracy WSL Institute for Snow and Avalanche Research SLF34

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3.2Results: Spatial correlations WSL-Institut für Schnee- und Lawinenforschung SLF36

3.2Results: Spatial correlations WSL-Institut für Schnee- und Lawinenforschung SLF37

3.2Results: Spatial correlations WSL-Institut für Schnee- und Lawinenforschung SLF38