AMSR-E/Aqua L1A Raw Observation Count, 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.

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

Citing These Data

We kindly request that you cite the use of this data set in a publication using the following citation. For more information, see our Use and Copyright Web page.

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

Overview

Platform

AQUA

Sensor

Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E)

Spatial Coverage

Coverage is global between 89.24°N and 89.24°S.

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.

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.

Parameters

Observation counts
Antenna temperature coefficients
Offsets for calculating antenna temperatures
Calibration temperature counts
Ancillary Data

Data Format

HDF

Metadata Access

View Metadata Record

Version

V3. See the AMSR-E Data Versions Web page for previous version information.

Get Data

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

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

  • 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.

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 Name: P1AME020602173MA_P01A0000000.00

P1AMEYYMMDD###MX_P###0000000.00

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

Where:

Table 1. File Naming Convention Description
Variable 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

File Size

Each half-orbit granule is approximately 37.5 MB.

Volume

The daily data rate is approximately 1.2 GB.

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
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.

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.

Parameter or Variable

See Level-1A data fields for details.

3. Data Access and Tools

Get Data

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

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.

4. Data Acquisition and Processing

Data Acquisition Methods

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

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:

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.

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.

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 acronyms used in this document are listed in Table 7.

Table 7. Acronyms and Abbreviations
Acronym Description
AMSR-E Advanced Microwave Scanning Radiometer - Earth Observing System
ASCII American Standard Code for Information Interchange
DAAC Distributed Active Archive Center
EASE-Grid Equal Area Scalable Earth-Grid
EOS Earth Observing System
EOSDIS EOS Data and Information System
FTP file transfer protoco
GHCC Global Hydrology Climate Center
HDF-EOS Hierarchical Data Format - EOS
JAXA Japan Aerospace Exploration Agency (JAXA)
JPL Jet Propulsion Laboratory (NASA)
NASA National Aeronautics and Space Administration
PO.DAAC Physical Oceanography Distributed Active Archive Center
QC Quality Control
RSS Remote Sensing Systems
SIPS Science Investigator-led Processing System
SMMR Scanning Multichannel Microwave Radiometer
SSM/I Special Sensor Microwave/Imager
TA Antenna temperature

Document Creation Date

February 2003

Document Revision Date

September 2011

Document URL

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