The influence of spatial variability of polar firn on microwave emission Martin Proksch 1, Henning...
-
Upload
liane-lenz -
Category
Documents
-
view
214 -
download
0
Transcript of The influence of spatial variability of polar firn on microwave emission Martin Proksch 1, Henning...
The influence of spatial variability of polar firn on microwave emission
Martin Proksch1, Henning Löwe1, Stefanie Weissbach2, Martin Schneebeli1
1 WSL-Institute for Snow- und Avalanche Research SLF, Davos, CH2 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 SLF 2
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 SLF 3
1. Motivation II • Where to measure (Sampling design)?
• Answer requires knowledge about snow variability!
Pic: Martin Schneebeli
4WSL-Institut für Schnee- und Lawinenforschung SLF
2.1 Instrument: 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
2.2 Measurements at Kohnen Station:Density
WSL-Institut für Schnee- und Lawinenforschung SLF 8
92 SMP profiles with interval 0.5 m -> 45m transect:
2.2 Measurements at Kohnen Station:Correlation length lex
WSL-Institut für Schnee- und Lawinenforschung SLF 9
92 SMP profiles with interval 0.5 m -> 45m transect:
2.2 Measurements at Kohnen Station:specific surface area SSA
WSL-Institut für Schnee- und Lawinenforschung SLF 10
92 SMP profiles with interval 0.5 m -> 45m transect:
3.1 MEMLS simulations
WSL-Institut für Schnee- und Lawinenforschung SLF 11
MEMLS: Microwave Emission Model of Layered Snowpacks, Wiesmann and Mätzler, 1999.
-> with Improved Born Approximation, Mätzler 1998.
MEMLS input: • 1cm layer thickness in top most meter• lex: SMP (no «grain size» scaling)• Density: SMP• Snow temperature profile• Tsky: 0K• Snow-ground reflectivity: 0• 20m deep profile, linearly increasing
3.2 Results: Brightness temperatures
WSL-Institut für Schnee- und Lawinenforschung SLF 12
σ Tb
Tb
3.2 Results: Brightness temperatures
WSL-Institut für Schnee- und Lawinenforschung SLF 13
σ Tb
Tb
3.2 Results: Brightness temperatures
WSL-Institut für Schnee- und Lawinenforschung SLF 14
One MEMLS run per SMP profile, total N = 92
σ(Tb, 36GHz) = 16.6 K
WSL-Institut für Schnee- und Lawinenforschung SLF 14
σ Tb
Tb
3.2 Results: Brightness temperatures One MEMLS run
per SMP profile, total N = 92
σ(Tb, 36GHz) = 16.6 K
To decrease σ, we have to increase the number of measurements N:
σ(Tb) = 16 K for N=92
σ(Tb) = 8 K for N = 368
σ(Tb) = 2 K for N = 2944
WSL-Institut für Schnee- und Lawinenforschung SLF 15
σ Tb
Tb
3.2 Results: Summit
17
Standard deviations:
• T19GHz, V-pol = 13.9 K
• T36GHz, V-pol = 24.1 K
• T89GHz, V-pol = 23.5 K
Constant Density: Constant corr. length
• T19GHz, V-pol = 13.5 K T19GHz, V-pol = 3.7 K T36GHz, V-pol = 26.1 K T36GHz, V-pol = 3.8 K T89GHz, V-pol = 27.8 K T89GHz, V-pol = 7.0 K
3.2 Results: Point Barnola
WSL-Institut für Schnee- und Lawinenforschung SLF 18
Standard deviations:
• T19GHz, V-pol = 3.3 K
• T36GHz, V-pol = 11.0 K
• T89GHz, V-pol = 21.2 K
Constant Density: Constant corr. length
• T19GHz, V-pol = 4.5 K T19GHz, V-pol = 1.2 K T36GHz, V-pol = 12.8 K T36GHz, V-pol = 1.5 K T89GHz, V-pol = 23.7 KT89GHz, V-pol = 4.3 K
3.3 Results: Spatial correlations
WSL-Institut für Schnee- und Lawinenforschung SLF 19
3.3 Results: Spatial correlations
WSL-Institut für Schnee- und Lawinenforschung SLF 20
3.3 Results: Spatial correlations
WSL-Institut für Schnee- und Lawinenforschung SLF 21
3.3 Results: Spatial correlations
WSL-Institut für Schnee- und Lawinenforschung SLF 22
3.3 Results: Spatial correlations
WSL-Institut für Schnee- und Lawinenforschung SLF 23
3.3 Results: Spatial correlations
WSL-Institut für Schnee- und Lawinenforschung SLF 24
3.3 Results: Spatial correlations
WSL-Institut für Schnee- und Lawinenforschung SLF 25
3.4 Results: Layer thickness
WSL-Institut für Schnee- und Lawinenforschung SLF 26
• 20m deep profile: – First meter SMP measurement– 2 – 20 meter: linear increasing, with random noise added.
3 cm
20 cm
3.4 Results: Effect of vertical averaging
WSL-Institut für Schnee- und Lawinenforschung SLF 27
Averaging to 3cm layer thickness leads to significant loss of density variations!
4. Summary and Conclusions
WSL-Institut für Schnee- und Lawinenforschung SLF 28
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 SLF 29
Thank you!
Thanks to:Christian MätzlerLudovic Brucker
WSL-Institut für Schnee- und Lawinenforschung SLF 30
WSL-Institut für Schnee- und Lawinenforschung SLF 31
3.5 Results: Measurement accuracy
WSL-Institut für Schnee- und Lawinenforschung SLF 32
• Meas. accuracy in top most meter
• To model Tb within 1K
Outlook
• Compare to SSMI
WSL Institute for Snow and Avalanche Research SLF 33
To do:
• Spat var - for other stations
• Layer thickness
• Meas accuracy
WSL Institute for Snow and Avalanche Research SLF 34
3.2 Results: Spatial correlations
WSL-Institut für Schnee- und Lawinenforschung SLF 36
3.2 Results: Spatial correlations
WSL-Institut für Schnee- und Lawinenforschung SLF 37
3.2 Results: Spatial correlations
WSL-Institut für Schnee- und Lawinenforschung SLF 38