Development of AMSR and AMSR-E retrieval algorithms at EORC
Keiji Imaoka
Earth Observation Research Center / NASDA
1. Introduction
The Advanced Microwave Scanning Radiometer (AMSR) is a multi-frequency, dual-polarized microwave
radiometer that detects microwave emissions from the Earth's surface and atmosphere. Various geophysicalparameters, particularly those related to water (H2 O), can be estimated from AMSR data. In addition to theproven parameters such as water vapor, precipitation, and sea surface wind speed, novel geophysical parameters,including sea surface temperature and soil moisture, are expected to be retrieved by using new frequency channels.
The largest ever microwave radiometer antenna enables us to perform continuous global observation with highspatial resolution. Long-term records of AMSR measurements will play an important role in climate changemonitoring as well as in providing indispensable information for understanding the Earth's climate system,including water and energy circulation. Near-real-time products will be used for investigating satellite data
assimilation into weather forecasting models and will contribute to improving forecast accuracy. In thistechnical report, we will summarize the theoretical basis and descriptions of an each retrieval algorithm.
2. Algorithm Development
NASDA issued the first Research Announcement (RA) in October 1995 to solicit standard algorithms forADEOS-II AMSR and GLI. Standard algorithms will be installed at the Earth Observation Center (EOC) to
operationally produce Level 2 and 3 geophysical products. The AMSR sensor team was organized based on thisannouncement. After the decision of providing AMSR-E to the EOS PM-1 satellite, the team has also been
responsible for AMSR-E standard algorithms. Retrieval algorithms for AMSR standard products have been
evaluated and selected through an algorithm inter-comparison proces s by the AMSR sensor team. Theinter-comparison procedure was mainly based on a comparison between in-situ or aircraft data and retrieved
geophysical parameters from brightness temperatures of existing space-borne sensors such as the Special Sensor
Microwave/Imager (SSM/I). Although the comparison showed little differences in the performance ofalgorithms, the day-1 algorithms (i.e. the algorithms at launch phase) and supporting PIs were selected based on
this result (e.g. whether he or she could meet report and program deadlines). The AMSR algorithm selection
board was held at EORC in May 2000. As a result of this board, the soil moisture product was re-defined as aresearch product at the launch phase due to the difficulties of accurate retrieval. For geophysical parameters with
two algorithm candidates, one algorithm was selected as standard and the other one was positioned as a researchalgorithm. Current day-1 algorithm investigators are listed in Table 1. These day-1 algorithms will be used atEOC during the first six-months after launch. After the real AMSR brightness temperatures are obtained, thisselection will be re-shuffled, and one algorithm will be selected based on its real performance. Through the 2nd
Research Announcement, several PIs have joined the project as research algorithm investigators. These PIs will
be added to the list at the next opportunity.
Table 1. Day-1 algorithms for AMSR and AMSR-E
Geophysical products
Integrated water vapor
Integrated cloud liquid water
Precipitation
Sea surface wind speed
Sea surface temperature
Sea ice concentrationSnow depth
Soil moistureStandard
Takeuchi
Wentz
Petty
Shibata
Shibata
ComisoChang-ResearchLiu
Wentz
Koike
Njoku, Jackson,Paloscia, Koike

3. Algorithm integration testing
EORC is responsible for proto-typing and testing the AMSR data retrieval system. We asked the algorithm
PIs to submit their source codes for retrieval algorithms. Prior to this request, NASDA distributed the “commonlibrary,” that is a kind of interfacing toolkit between the PI environment and the NASDA processing system. We
can easily integrate PI source codes written using this common library into our processing system. During fiscal
year 2000, we were provided the algorithms twice, corresponding to the distributions of different version of thecommon library. Since the AMSR has not flown yet, no real brightness temperatures are available to check thecondition and performance of each algorithm. As the input data for the testing, we generated AMSR simulated
brightness temperatures by using existing microwave radiometer data such as SSM/I and SMMR with slightcorrections for incident angle and center frequencies. Radiative transfer calculations were also used fornonexistent frequency channels. Through the algorithm integration testing, we have confirmed that most of thealgorithms functioned properly. Since the AMSR simulated data are not ideal, we have to wait for the real
AMSR data to investigate algorithm performance. Sample browse images of the retrieval results are shown in Fig.
1.

Fig. 1. Global images generated by AMSR processing system at EORC. Images of sea surface wind speed (left)
and sea surface temperature (right) are shown as examples. Input data are AMSR simulated ascending passes onJune 24, 1998.