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AMSR-E/Aqua L1A Raw Observation Counts

Summary

The Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) instrument on the NASA EOS Aqua satellite provides global passive microwave measurements of land, ocean, and atmospheric variables for the investigation of global water and energy cycles.

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. Each half-orbit data granule consists of observation counts, antenna temperature coefficients, offsets for calculating antenna temperatures, calibration temperature counts, land/ocean flags, time, latitude, longitude, and navigation fields in HDF format.

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. Each swath spans 50 minutes. Data are available via FTP.

Citing These Data

The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.

Japan Aerospace Exploration Agency. 2003, updated daily. AMSR-E/Aqua L1A Raw Observation Counts. Version 3. [indicate subset used]. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.5067/AMSR-E/AMSREL1A.003.

Overview Table

Category Description
Data format HDF
Spatial coverage and resolution Coverage is global between 89.24°N and 89.24°S, except where gaps occur between satellite swaths. 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.
Temporal coverage and resolution See AMSR-E Data Versions for a summary of temporal coverage for different AMSR-E products and algorithms. Each half-orbit granule spans 50 minutes.
File naming convention Example: "P1AME020602173MA_P01A0000000.00"
File size Each half-orbit granule is approximately 37.5 MB.
Parameter(s) Observation counts, antenna temperature coefficients, offsets for calculating antenna temperatures, calibration temperature counts, and ancillary data
Procedures for obtaining data Please see Ordering AMSR-E Products from NSIDC for a list of order options.

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments

Investigator(s) Name and Title

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

Technical Contact

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

2. 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

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."

File Naming Convention

Following is an example of the file-naming convention for this product. The date corresponds to the first scan of the granule.

P1AME020602173MA_P01A0000000.00

Where:

P1 = Aqua satellite (PM-1)
AME = AMSR-E sensor
02 = Two-digit year (2002, in this example)
06 = Two-digit month (June, in this example)
02 = Day
173 = Path number
M = Orbital mode (A = ascending pass)
P = Product type (01A = Level 1A product)

File Size

Each half-orbit granule is approximately 37.5 MB.

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:

Spatial coverage of AMSR-E instrument

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.

Temporal Coverage

See AMSR-E Data Versions for a summary of temporal coverage for different AMSR-E products and algorithms.

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.

Parameter or Variable

See Level 1A data fields for details.

Error Sources

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

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.

3. Data Access and Tools

Data Access

Please see Ordering AMSR-E Products from NSIDC for a list of order options.

Volume

Each half-orbit granule is approximately 37.5 MB. The daily data rate is approximately 1.2 GB.

4. Data Acquisition and Processing

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.

Data Acquisition Methods

See the AMSR-E Instrument Description for more information.

Data Source

The Japan Aerospace Exploration Agency (JAXA) processed AMSR-E Level 0 data into Level 1A observation count data.

Formulae

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:

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:

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:

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:

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.

Processing 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.

5. References and Related Publications

Mitsubishi Electric Corporation. 2000. EOS-PM AMSR-E Data Processing System: Level 1A Format Description Document. GAMSRE-E-037. Tokyo: Mitsubishi Electric Corporation.

6. Document Information

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document:

Document Creation Date

February 2003

Document Revision Date

12 July 2005

Document Review Date

February 2003

Document URL

http://nsidc.org/data/docs/daac/amsrel1a_raw_counts.gd.html

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