Status of calibration and data evaluation of AMSR on board ADEOS-II

1
Status of calibration and data evaluation of AMSR
on board ADEOS-II

• Keiji Imaoka a, Yasuhiro Fujimoto a, Misako Kachi
  a, Toshiaki Takeshima a, Tamotsu Igarashi a,
  Toneo Kawanishi b, and Akira Shibata aa Earth
  Observation Research Center, NASDAb ALOS project
  team, NASDASPIE International Symposium in
  Remote Sensing EuropeBarcelona, SpainSeptember
  8, 2003

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AMSR TB at all channels (path 11, January 18,
2003)
6V
6H
10V
10H
18V
18H
23V
23H
36V
36H
89AV
89AH
89BV
89BH
50.3V
52.8V
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Characteristics of AMSR

• Multifrequency, dual-polarized passive microwave
  radiometer developed by NASDA.
• Higher spatial resolution compared to existing
  instruments (e.g., SSM/I).
• Addition of 6.9-GHz channels for estimating SST
  and soil moisture, and 50.3 and 52.8GHz for
  obtaining atmospheric temperature information.
• Flying in morning orbit (equatorial crossing
  time 1030 am). Combination with AMSR-E on Aqua
  (130 pm) will provide information on diurnal
  variability.

AMSR performing conical scan measurement in
orbit. Original ADEOS-II animation can be
obtained from NASDA website http//www.nasda.go
.jp/
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TB images of 50GHz channels
First look of 52.8-GHz channel by conically
scanning radiometer.
53.6GHz 4 km
52.8GHz 1 km

• No limb correction is necessary.
• Incidence angle of 55 degrees results in
  approximately 2 to 3 km of weighting peak.

AMSU-A daily browse from http//pm-esip.msfc.nasa.
gov/
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AMSR/AMSR-E combination

• Combination of AMSR-E and AMSR will be a powerful
  tool to investigate rapidly changing phenomena
  and diurnal cycle.
• Cross calibration will be important to keep
  consistency between AMSR and AMSR-E data.

Example of storm tracking by combining AMSR and
AMSR-E observations. Processed by using NASDA
standard algorithm developed by Dr. Petty (Univ.
of Wisconsin-Madison). Rainfall rates are under
validation.
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Characteristics of AMSR

• Non-deployable, offset parabolic antenna with
  effective aperture size of 2.0 m.
• Total power microwave radiometers.
• High Temperature noise Source (HTS) and Cold Sky
  Mirror (CSM) for onboard two-point calibration.
• Two feed horns for 89GHz to keep enough spatial
  sampling in along track direction.

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Direction of work

• AMSR and AMSR-E are almost identical instruments
  in terms of radiometric characteristics. Same
  problem exists in HTS performance (inhomogeneous
  physical temperature).
• Although we have to take into account the
  differences on thermal condition of the
  instruments (i.e., different local observing
  times), which is very important to calibration,
  direction of calibration activities are almost
  identical.
• Base on discussions in course of the examination,
  the final calibration method may differ from the
  current approaches.

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Radiometer sensitivity
Time series of radiometric sensitivity while
observing HTS (around 300K).
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Lunar emission in cold cal.

• Moon sometimes comes insight of CSM view angle
  and affects the cold calibration counts sometimes
  up to 30K in 89 GHz due to its small beam size
  compare to other frequencies.
• Correction is relatively straightforward since
  direction of the moon can be computed. After
  removed the affected counts, simple linear
  interpolation is applied to fill the gap in L1
  processing system.

AMSR CSM Output Voltages (March 22, 2003, Path
No. 40, Ascending)
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Earth emission in cold cal.

• 6.925-GHz CSM counts seem to be affected by
  Earths emission (up to 1K).
• Our current assumption is that this phenomena is
  due to a spillover occurring between feed horn
  and CSM.
• Earths emission pattern is relatively unclear in
  AMSR case. One possible explanation is a
  different satellite structure that may intercept
  the spillover path and obscure the Earths
  emission pattern.

AMSR-E
AMSR
Comparison of the Earths emission effect between
AMSR-E and AMSR. Psaudo maps are made of 233 and
57 descending paths for AMSR-E and AMSR,
respectively.
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Land emission in cold cal.

• Correlation was found between variations of
  contamination and Earths Tb of about 110 scans
  before.
• L1 processing system subtract this contamination
  by assuming CSM spillover (spillover occurring
  between feed horn and CSM) Spillover factor was
  statistically found and used for correction.

Before
After
Sample images showing the correction. Maps are
made of 57 descending paths.
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Radiometric correction
Step 1 PRT method
Step 2 RxT method

• Multiple regression model of Teff using eight PRT
  readings.
• Coefficients of the regression model were
  determined by using SSM/I oceanic Tb (18GHz and
  higher channels) and computed Tb (6 and 10GHz
  channels) based on the Reynolds OI-SST analysis.
• SSM/I data were provided by the Global Hydrology
  Resource Center (GHRC) at the Global Hydrology
  and Climate Center, Huntsville, Alabama, USA.
  Reynolds OI-SST dataset were made available by
  NOAA.

• Utilize Relationship between receiver temperature
  and its gain variation.
• Applying this equation to HTS measurement and
  assuming Teff derived by regression model as
  TOBS, bRX can be computed by regression analysis.
  Using this value, gain variations can be
  compensated by the equation.

PRT readings
HTS Effective Temp.
TOBS Scene Tb (K) TCSM Deep space Tb
(K) COBS Digital counts of scene CCSM
Digital counts of deep spece G0 Nominal
gain bRX Gain sensitivity to rec. temp.
(?-1) DTRX Rec. temp. departure from mean value
(?).
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HTS effective temperature
Ta
HTS Temp. (target)
TH
SSM/I or simulated Earth Tb
TOBS
Deep space Temp.
TC
Counts
CC
COBS
CH
AMSR-E measurement
Extrapolating HTS effective temperature (target)
by using Earth Tb
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Combining PRT and RxT
From PRT method
23GHz Vpol Tb_HTS Treciever
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Improvement by adding RxT method
BLUE HTS effective temp. by PRT method.
REDHTS effective temp.by PRTRxT method.
REDDifference between above two.
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Radiometric correction6.925GHz tentative results
Comparison between computed Tb based on OI-SST
and AMSR Tb by (a) simple two-point calibration
and (b) presented method for 6.925-GHz vertical
polarization on June 3, 2003. (c) Daily average
of difference between computed and AMSR Tb as a
function of position in orbit for simple
two-point calibration (cross) and presented
method (closed circle).
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Radiometric correction36.5GHz tentative results
Comparison between SSM/I Tb (corrected for
difference of incidence angle and center
frequency) and AMSR Tb by (a) simple two-point
calibration and (b) presented method for 36.5-GHz
vertical polarization on June 3, 2003. (c) Daily
average of difference between SSM/I Tb and AMSR
Tb as a function of position in orbit for simple
two-point calibration (cross) and presented
method (closed circle).
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AMSR and AMSR-E comparison
It should be noted that AMSR TB are still
tentative version.
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6.925GHz RFI
6.925GHz vertical polarization, ascending passes
(July 8, 2003)
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Known issues and on-going works

• Possible overestimation in high Tb over land in
  6.925 GHz. Suspect receiver non-linearity
  characteristics.
• Need further improvement particularly at lower
  frequency channels (for SST, etc.).
• Comparison of 50GHz channels TB with AMSU TB with
  an incidence angle of near 55 degrees.
• Utilization of SeaWinds wind speed data to
  minimize the uncertainties in comparing AMSR TB
  and computed TB based on Reynolds-SST.
• Comparison of AMSR and AMSR-E to keep these data
  set consistent.
• Assessment of other systematic errors (e.g., scan
  bias).
• Assessment of geolocation errors (errors may not
  be corrected if its size does not exceeds that of
  AMSR-E).

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Summary and conclusions

• AMSR is providing stable data stream since the
  beginning of normal operation.
• Same approaches (that were applied to AMSR-E) of
  post-launch evaluation and calibration are being
  tested. Some preliminary results of calibration
  were presented.
• Our current target date of releasing the data is
  after 1-year from ADEOS-II launch.

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AMSR-E data status

• NASDA/EOC started distribution of AMSR-E L1
  brightness temperature (and L3-Tb) products from
  June 18, 2003.
• http//www.eoc.nasda.go.jp/amsr-e/index_e.html
• http//www.eorc.nasda.go.jp/AMSR
• ? AMSR-E Data Release
• L1A (raw counts) data are also available at
  NSIDC.
• http//nsidc.org
• ? Data catalog
• ? AMSR-E/Aqua L1A Raw Observation Counts