AMSR2 L1R ProductJapan Aerospace Exploration Agency
Earth Observation Research Center
Takashi Maeda
Apr. 8, 20131

Contents• Concept• Implementation• Validation Results• Summary2

Difference of an observation area (footprint)
at the same pixel numbere. g.)
250 K @ 89 GHz
200 K @ 6.925 GHz

Can we treat them as the data from the same location?

No!
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To use the data with different footprints equivalently...
• Synthesis of the data in appropriate coefficients.
Small footprints (antenna pattern) are collected and synthesized, then largefoot print (antenna pattern) is duplicated from them at any position.
89 GHz

L1B

6.925 GHz4

To use the data with different footprints equivalently...
• Synthesis of the data in appropriate coefficients.
Small footprints (antenna pattern) are collected and synthesized, then largefoot print (antenna pattern) is duplicated from them at any position.
89 GHzLarge coefficient at a high gain point

L1B

Small coefficient at a low gain point
6.925 GHz5

To use the data with different footprints equivalently...
• Synthesis of the data in appropriate coefficients.
Small footprints (antenna pattern) are collected and synthesized, then largefoot print (antenna pattern) is duplicated from them at any position.
89 GHzVirtual Tb of 89 GHz observed by the antenna
pattern of 6.9 GHz.

L1R
L1B

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Tb data stored in L1R product
Criteria:
Small footprints (antenna pattern) are collected and synthesized, then largefoot print (antenna pattern) is duplicated from them at the geolocations of89 GHz (A).
TARGET ANTENNA PATTERNSOURCE ANT. PATTERN

6.925 GHz

10.65 GHz

23.8 GHz

36.5 GHz

6.925 GHzO

7.3 GHzO10.65 GHzOO

18.7 GHzOOO

23.8 GHzOOO

36.5 GHzOOOO

89 GHzOOOO* O : Because the footprint sizes of source and target antennapatterns are same, these are operations to move the geolocationsof the source antenna patterns to those of 89 GHz (A).
* The antenna pattern of 18.7 GHz does not become a target
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because its size is almost the same as that of 23.8 GHz.

Additional processing : altitude correction
A geolocation finally stored in L1R is corrected using the altitude at it.
Corrected geolocation
approaches L (H tan Θ)
to the satellite.

Original geolocation

Accordingly, the geolocations of 89 GHz (A) and (B) in L1R differ from thosein L1B in land areas.
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Theoretical background : Backus‐Gilbert Method
Gi (i = 1 ... p) : the antenna patterns of f1 GHz↓
F : the antenna pattern of f2 GHz
Coefficients ai are calculated asκ : parameter to control the quality of synthesis (0 ~ ∞)― volume of Gi― crossover's volume of Gi and F― crossover's volume of Gi and Gjκ is always set to 0.0001 with reference to AMSR‐E L2A product right now.
9Contents• Concept• Implementation• Validation Results• Summary
10Antenna pattern used in L1R processing (e.g., 6.925 GHz V)

Ant. pattern measured at a ground test (8241 sampling points)
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Projection to the ground from the nominal altitude of AMSR2 (700 km)

12Normalization of volume to 1.0 for BG Method

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Cutoff under ‐30 dB (0.1%) of the highest gain

volume ≈ 0.996

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9 times broader than the nominal
foot print size (35 x 62 km2)

170 km120 kmOther antenna patterns are created along the same criteria.
15Synthesis of antenna pattern (e.g., 89 GHz V → 6.925 GHz V)

M px

Always M = 30, N = 30

N px

M px

N px

A large antenna pattern is always synthesized from3721 (61 x 61) small antenna patterns.

16However, considering the antenna pattern alignment in a swath, ...
#122(#243)#243(#486)#1

the number of small antenna patterns required to completely covera large antenna pattern varies depending on the position in a swath.
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If M = 15 and N = 15, ... (cf. M = 14, N = 14 for AMSR‐E L2A)

The range for high‐quality L1R Tb is
too narrow!

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Therefore, M = 30 and N = 30, then ...

The range for high‐quality L1R Tb isexpanded to the max.

Deterioration of coverage,
eventually the quality of L1R Tb, atthe swath edge is inevitable. So,
this information is provided tousers for reference.

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(Ref.) Coverage to synthesize ...
ex.) source : 89.0 GHz (A), target: 6.925 GHz

coverage : 100%at the pixel in the center of a swath

antenna pattern of 6.925 GHz V

coverage : 77.12%
at the pixel in the edge of a swath

If the coverage of source antenna patterns (S) for the target antenna
pattern (T) is 100%, T can be completely synthesized by S. However,as the pixel number goes to the edge of a swath, T cannot becompletely covered with S because no pixels exist beyond the edgeof the swath. Accordingly, a resampling filter as T is completely
synthesized by S cannot be obtained in such cases, so that thequality of resampled brightness temperatures calculated by such
filters deteriorates.

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(Ref.) Coverage to synthesize ...

antenna pattern of 6.925 GHz H
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(Ref.) Coverage to synthesize ...

antenna pattern of 10.65 GHz V

antenna pattern of 10.65 GHz H
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(Ref.) Coverage to synthesize ...

antenna pattern of 23.8 GHz V

antenna pattern of 23.8 GHz H
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(Ref.) Coverage to synthesize ...

antenna pattern of 36.5 GHz V

antenna pattern of 36.5 GHz H
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Contents• Concept• Implementation• Validation Results• Summary
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Instance of geometric validation results
R: L1R Tb of 6.9 GHz V
G: L1R Tb of 10.65 GHz Vby synthesized ant. pattern of 6.9 GHz V
B: L1R Tb of 6.9 GHz V

It is assumed that Tb values at these 3channels are observed by the antenna
pattern of 6.9 GHz V located at the sameposition.
Therefore, coastlines must fit closely
between L1R Tb of 6.9 and 10.65 GHz V.
Actually, green (#00FF00) or magenta(#FF00FF) lines do not appear along
coastlines.
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Contents• Concept• Implementation• Validation Results• Summary27

Summary• AMSR2 L1R productimplemented based on BG Method– Parameters (e.g., M, N) are determined as high‐quality L1RTb can be obtained in the widest possible range of a swath.
– Deterioration of the quality of L1R Tb is inevitable at theswath edge.

• Good geometric validation results

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