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Data Set ID:
AMSREL1A

AMSR-E/Aqua L1A Raw Observation Counts, Version 3

AMSR-E Level-1A observation counts are processed from Level-0 science packet data by the Japan Aerospace Exploration Agency (JAXA) Earth Observation Center (EOC) in Japan.

Version Summary:

The improved V003 AMSREL1A product features empirical corrections to the co-registration parameters A1 and A2, and an updated parameter file used for correcting the AMSR-E 89 GHz position information. As a result, Version 3 AMSREL1A data provide improved accuracy for the following: Latitude and Longitude, land/ocean flags, earth incidence angle, earth azimuth angle, sun azimuth angle, and sun elevation angle. Additionally, the HDF-EOS version was updated from 4.2r1 to 4.2r4.

Geographic Coverage

Parameter(s):
  • Microwave > Sensor Counts
Spatial Coverage:
  • N: 90, S: -90, E: 180, W: -180

Spatial Resolution: Not Specified
Temporal Coverage:
  • 1 June 2002 to 4 October 2011
(updated daily)
Temporal Resolution: 50 minute
Data Format(s):
  • HDF
Platform(s) AQUA
Sensor(s): AMSR-E
Version: V3
Data Contributor(s): Japan Aerospace Exploration Agency (JAXA).
Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Japan Aerospace Exploration Agency (JAXA). 2003, updated daily. AMSR-E/Aqua L1A Raw Observation Counts, Version 3. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/AMSR-E/AMSREL1A.003. [Date Accessed].

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Detailed Data Description

Format

Level-1A data are in Hierarchical Data Format (HDF) with the following contents:

AMSR-E Level-1A Header

Level-1A Data Fields

  • Navigation and attitude data
  • Observation counts
  • Calibration temperature counts
  • Antenna temperature coefficients
  • Time
  • Latitude
  • Longitude
  • Sun azimuth
  • Sun elevation
  • Earth incidence
  • Earth azimuth
  • Data quality

The dimension of observation count data is 243 observations by approximately 2003 scans for all channels except 89.0 GHz. The dimension of 89.0 GHz data is 486 observations by approximately 2003 scans. The number of scans may fluctuate slightly. Missing data are indicated by a value of -9999.999.

For more information on the data fields' format descriptions, see Aqua AMSR-E Level 1 Product Format Description Document

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File Naming Convention

This section explains the file naming convention used for this product with an example. The date and time correspond to the first scan of the granule.

Example File NameP1AME020602173MA_P01A0000000.00

P1AMEYYMMDD###MX_P###0000000.00

Refer to Table 1 for the valid values for the file name variables listed above.

Where:

Variable Description
Table 1. File Naming Convention Description
P1 Aqua satellite (PM-1)
AME AMSR-E sensor
YY Two-digit year
MM Two-digit month
DD 2-digit day
### Path number
MX Orbital mode (A = ascending pass)
P### Product type (01A = Level-1A product)

Table 2 provides examples of file name extensions for related files that further describe or supplement data files.

Table 2. Related File Extensions and Descriptions
Extensions for Related Files Description
.brws Browse data
.qa Quality assurance information
.ph Product history data
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File Size

Each half-orbit granule is approximately 37.5 MB.

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Volume

The daily data rate is approximately 1.2 GB.

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Spatial Coverage

Coverage is global between 89.24°N and 89.24°S, except where gaps occur in a single day of observations, as the spatial coverage map shows. Multiple days of data produce no gaps in coverage. See AMSR-E Pole Hole for a description of gaps that occur at the North and South Poles.

Spatial Coverage Map

The following map shows a typical day of coverage:

Figure 1. Spatial Coverage Map

Spatial Resolution

The sampling interval at the earth's surface is 10 km for the 6.9 GHz to 36.5 GHz channels, and 5 km for the 89.0 GHz channel. Please see 89 GHz Scan Spacing for a figure that summarizes sampling intervals.

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Temporal Coverage

Temporal coverage is from 1 June 2002 to 4 October 2011.

Temporal Resolution

The data sampling interval is 2.6 msec for each 1.5 sec scan period for the 6.9 GHz to 36.5 GHz channels, and 1.3 msec for the 89.0 GHz channel. AMSR-E collects 243 data points per scan for the 6.9 GHz to 36.5 GHz channels, and 486 data points for the 89.0 GHz channel.

The number of satellite passes per day is a function of latitude, as shown in AMSR-E Observation Times.

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Parameter or Variable

See Level-1A data fields for details.

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Software and Tools

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Quality Assessment

Level-1A quality flags are provided with the AMSR-E/Aqua L2A Global Swath Spatially-Resampled Brightness Temperatures (Tb) data set. Users should obtain the corresponding Level-2A data granule to see quality flags for a given Level-1A granule. Note, however, that there is no 1:1 mapping between the two sets of flags. Users should match the Level-1A quality flags with the corresponding time of acquisition.

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Data Acquisition and Processing

Data Acquisition Methods

See the AMSR-E Instrument Description Web page for more information.

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Derivation Techniques and Algorithms

Apply the procedures described below to derive brightness temperatures using JAXA's calibration.

Step 1

Convert the observation count data into antenna temperatures by the following formula.

Ta = Asl * Obs + Aof

Where:

Table 3. Step 1 Formula
Variable Description
Ta Antenna temperature (K)
Asl Antenna temperature conversion coefficient (slope value)
Obs Count value of observation data
Aof Antenna temperature conversion coefficient (offset value)

The offset and slope values of the antenna temperature conversion coefficient are stored in the Antenna_Temperature_Coef(Of+Sl) attribute of this Level-1A data product.

Step 2

Correct the scan bias for 6 GHz only by using the following formula.

Ta' = Ta * Cog[i]

Where Cog[i] is the scan bias coefficient for 6 GHz only. (i: observation point in the range of the Level-1B product.)

See Scan Bias Coefficients or download a table of coefficients (Excel file, 28 KB).

Step 3

Correct the non-linear calibration using the following formula.

Ta'' = C0 + C1 Ta' + C2 (Ta')2 + C3 (Ta')3 + C4 (Ta')4

Where:

Table 4. Step 3 Formula
Variable Description
Ta'' Nonlinear calibrated antenna temperature (K)
C0 — C4 Calibration Curve Coefficient#1 - #5
Ta' Antenna temperature calculated with antenna temperature coefficients (K)

The calibration curve coefficients #1- #4 are stored in the CalibrationCurveCoeficient#1 -#5 attribute of this Level-1A data product.

Step 4

Convert the antenna temperature into a brightness temperature using the following formula.

Tbv = Avv Ta''v + Ahv Ta''h + 2.7 Aov

Where:

Table 5. Step 4 Formula
Variable Description
Tbv Observation brightness temperature of the vertical polarization
Avv Conversion coefficient of the vertical co-polarization
Ta''v Antenna temperature of the vertical polarization
Ahv Conversion coefficient of the vertical cross-polarization
Ta''h Antenna temperature of the horizontal polarization
Aov Coefficient of the deep space's brightness temperature of the vertical polarization

Tbh = Ahh Ta''h + Avh Ta''v + 2.7 Aoh

Where:

Table 6. Step 4 Formula 4b
Variable Description
Tbh Observation brightness temperature of the horizontal polarization
Ahh Conversion coefficient of the horizontal co-polarization
Ta''h Antenna temperature of the horizontal polarization
Avh Conversion coefficient of the horizontal cross-polarization
Ta''v Antenna temperature of the vertical polarization
Aoh Coefficient of the deep space's brightness temperature of the horizontal polarization

These conversion coefficients are stored in the CoefficientAvv – Aoh attribute of this Level-1A data product.

Processing Steps

Under normal operating conditions, Remote Sensing Systems (RSS) in Santa Rosa, California, receives Level-1A data from JAXA via the NASA Jet Propulsion Laboratory (JPL) Physical Oceanography Distributed Active Archive Center (PO.DAAC).

The calibration coefficients and offsets for this data set are determined by JAXA. They are different from those of the AMSR-E/Aqua L2A Global Swath Spatially-Resampled Brightness Temperatures (Tb), which are determined by RSS. The Level-1A data have not been calibrated; specifically, they were not converted from instrument counts to TAs. Coefficients are written to the Level-1A data but not applied.

Version History

Version 2 (V002) of this Level-1A product was released in March 2005 and uses a non-linear correction. This improved version features empirical corrections to the Aqua scan azimuth and satellite flight direction. With corrected sun azimuth, sun elevation, earth azimuth, and earth incidence angles, the geometric accuracy of AMSR-E 89 GHz data improved to within 2 km.

Version 3 (V003) of this Level-1A product was released in September 2011 and features empirical corrections to the co-registration parameters A1 and A2, and an updated parameter file used for correcting the AMSR-E 89 GHz position information. As a result, Version 3 AMSREL1A data provide improved accuracy for the following: Latitude and longitude, land/ocean flags, earth incidence angle, earth azimuth angle, sun azimuth angle, and sun elevation angle. Additionally, the HDF-EOS version was updated from 4.2r1 to 4.2r4.

Error Sources

The AMSR-E Instrument Description provides details on potential errors associated with radiometer calibration.

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Sensor or Instrument Description

Please refer to the AMSR-E Instrument Description document.

Calibration

AMSR-E's calibration system has a cold mirror that provides a clear view of deep space (a known temperature of 2.7 K) and a hot reference load that acts as a blackbody emitter; its temperature is measured by eight precision thermistors. After launch, large thermal gradients due to solar heating developed within the hot load, making it difficult to determine from the thermistor readings the average effective temperature, or the temperature the radiometer sees.

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References and Related Publications

Contacts and Acknowledgments

National Space Development Agency of Japan
Earth Observation Center
Chuo-ku, Tokyo, 104-6023
Japan

Document Information

Document Creation Date

February 2003

Document Revision Date

September 2011

No technical references available for this data set.

FAQ

How do the calibration coefficients differ between the Level-1A and Level-2A AMSR-E data sets?
The calibration coefficients and offsets for the AMSR-E/Aqua L1A Raw Observation Counts are determined by JAXA. They are different from those of the AMSR-E/Aqua L2A Global Swath Spatially-... read more