Improving the AMSR-E snow d epth p roduct: recent developments
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Improving the AMSR-E snow depth product: recent developments
Richard KellyUniversity of Waterloo, Canada.
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Outline
• Current product: performance of the satellite only product
• Development issues– RFI– Lake behaviour– Forest attenuation
• Observations and Conclusions
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Current snow depth product:Approach (AMSR-E observation-based)
where
fd=50%ff=40%
r=12.5km
fd=10%ff=40%
IFOV radius=12.5 kmForest stand
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Performance (2002-2003)
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comments
• Retrievals are conducted at the IFOV level (not at the grid-averaged level)
• Retrievals are then aggregated to coarser grid (0.25x025 deg)
• Tb correction (forest only) is built into the retrievals but not perfectly formulated.
• RFI and water bodies not well accounted for.
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RFI issues
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RFI
Kidd, C.(2006) 'Radio frequency interference at passive microwave earth observation frequencies’, International Journal of Remote Sensing,27:18,3853 — 3865
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MODIS-Daily2 Feb. 2009
3 Feb. 2009
4 Feb. 2009
5 Feb. 2009
6 Feb. 2009
7 Feb. 2009
8 Feb. 2009
9 Feb. 2009
10 Feb. 2009
From sat.dundee.ac.uk
RFI impacts
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UK AMSR-EDaily Snow 2.2.2009
Missing / badWater320 – 540160 - 32080 - 16040-801 - 400SWE [mm]
RFI impacts
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10V GHz 10V-36V (current)
5 February 2009
RFI impacts
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Adjusted retrievals without the use of the 10 GHz channel in UK.
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Lake issues
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• Much of the Arctic and sub-Arctic are dominated by lake cover (fractions of 40% not uncommon).
• At 25 km grid resolution lakes will play an important role
• But what is that role and can lake signals be identified?
• Time series of data for 9 years.
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Kang et al. (2010) GRSL 7(4)
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A note on gridding and AMSR-E measurement samples
10 km
10 k
m
AMSR-E sampling grid
25 km
LOI
Depending on the proximity threshold (x), may or may not be daily, but it will be for a consistent location
x
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Water Fraction0-10%
11-20%
21-30%
31-50%
>50%
Forest Fraction0%
1-10%
11-20%
21-30%
31-50%
>50%
0 400 km
MOD44W Water mask & MODIS VCF25 km diameter circle averaged on 1 km grid
25km
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Snow
dep
th (c
m)
Date
AMSR snow depth (0.25x0.25 deg gridded)
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Nearest WMO snow depth / air temperatureSn
ow d
epth
(cm
)
Date
Mean Tem
p (C)
0% FF & 37% WF
0% FF & 35% WF
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Tb (K
)
Date
AMSR Tbs (36V & 18V): centre within 4 km of locations of interest
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AMSR Tbs (36V & 18V)
Lake freeze-up
Snow
accumulation
on lake
Snow and
lake ice melt
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Forest fraction
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Water Fraction0-10%
11-20%
21-30%
31-50%
>50%
Forest Fraction0%
1-10%
11-20%
21-30%
31-50%
>50%
0 400 km
MOD44W Water mask & MODIS VCF25 km diameter circle averaged on 1 km grid
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Snow
dep
th (c
m)
Date
AMSR snow depth (0.25x0.25 deg gridded)
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AMSR Tbs (36V & 18V): centre within 4 km of locations of interestTb
(K)
Date
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Forest & lakes combined
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Water Fraction0-10%
11-20%
21-30%
31-50%
>50%
Forest Fraction0%
1-10%
11-20%
21-30%
31-50%
>50%
0 400 km
And when you mix forest and lakes….
MOD44W Water mask & MODIS VCF25 km diameter circle averaged on 1 km grid
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Snow
dep
th (c
m)
Date
AMSR snow depth (0.25x0.25 deg gridded)
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4% Water fraction and 55% forest fraction
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AMSR Tbs (36V & 18V): centre within 4 km of locations of interestTb
(K)
Date
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Areas of development• RFI can be accommodated in the current implementation by a of 10 GHz
observations with 18 GHz in the affected areas• Water fraction changes the nature of a Tb difference or ratio. 18 GHz is
sensitive to lake ice thickness so that DTb is not necessarily a function of DSD or SWE.
• Forest fraction/structure reduces sensitivity (known). But it is likely not a linear forest fraction attenuation effect
• Forest and water fraction together require correction before SWE inversion is applied. Recent work by Langlois et al. (2011) has demonstrated new approach to transmissivity correction and lake fraction can likely be corrected for (ongoing work)
• Operational implementation of forest and lake correction is yet to be completed.
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• Is it not time we began looking at grids that are higher resolution – 25 km EASE grid was chosen because the SSM/I 37 GHz approximate this resolution?
• AMSR-E/GCOM-W are at 10x14 km at 36 GHz. Perhaps a higher spatial resolution (e.g. 12.5km grid)?
Thank you