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AMSR-E/AMSR2 Unified L3 Daily 6.25 km Polar Gridded 89 GHz Brightness Temperatures, Version 1
The AMSR-E/AMSR2 Unified Level-3 6.25 km product includes brightness temperatures at 89.0 GHz. Data are mapped to a polar stereographic grid at a spatial resolution of 6.25 km for the Northern and Southern Hemispheres. This product uses the Japan Aerospace Exploration Agency (JAXA) AMSR2 Level-1R input brightness temperatures that are calibrated (unified) across the JAXA AMSR-E and AMSR2 Level-1R products.
This is the most recent version of these data.
COMPREHENSIVE Level of Service
Data: Data integrity and usability verified; data customization services available for select data
Documentation: Key metadata and comprehensive user guide available
User Support: Assistance with data access and usage; guidance on use of data in tools and data customization services
|
Geographic Coverage |
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Once you have logged in, you will be able to click and download files via a Web browser. There are also options for downloading via a command line or client. For more detailed instructions, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login. Earthdata Search: This application allows you to search, visualize, and access data across thousands of Earth science data sets. Additional customization services are available for select data sets, including subsetting, reformatting, and reprojection. Worldview: This application allows you to interactively browse global satellite imagery within hours of it being acquired. You can also save it, share it, and download the underlying data. |
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.
Meier, W. N., J. C. Comiso, and T. Markus. 2018. AMSR-E/AMSR2 Unified L3 Daily 6.25 km Polar Gridded 89 GHz Brightness Temperatures, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/NX1R09ORNOZN. [Date Accessed].Data Description
Parameters
This data set consists of brightness temperature (Tb) observations at 89.0 GHz. Tables 1 and 2 show the parameters associated with this data set.
|
Field Name |
Description |
|---|---|
SI_06km_NH_89V_ASC |
89.0 GHz vertical daily average ascending Tb |
SI_06km_NH_89V_DSC |
89.0 GHz vertical daily average descending Tb |
SI_06km_NH_89V_DAY |
89.0 GHz vertical daily average Tb |
SI_06km_NH_89H_ASC |
89.0 GHz horizontal daily average ascending Tb |
SI_06km_NH_89H_DSC |
89.0 GHz horizontal daily average descending Tb |
SI_06km_NH_89H_DAY |
89.0 GHz horizontal daily average Tb |
|
Field Name |
Description |
|---|---|
SI_06km_SH_89V_ASC |
89.0 GHz vertical daily average ascending Tb |
SI_06km_SH_89V_DSC |
89.0 GHz vertical daily average descending Tb |
SI_06km_SH_89V_DAY |
89.0 GHz vertical daily average Tb |
SI_06km_SH_89H_ASC |
89.0 GHz horizontal daily average ascending Tb |
SI_06km_SH_89H_DSC |
89.0 GHz horizontal daily average descending Tb |
SI_06km_SH_89H_DAY |
89.0 GHz horizontal daily average Tb |
Parameter Details
Missing or out-of-bounds grid cells have a value of 0. Data have a scale factor of 0.1. Multiply data values by 0.1 to obtain Tb in Kelvin (K). The valid range of Tb is approximately 50 K to 300 K.
File Information
Format
Data are stored in Hierarchical Data Format - Earth Observing System (HDF-EOS5) format.
File and Directory Structure
As shown in Figure 1, each data file includes twelve parameter fields (six Northern Hemisphere and six Southern Hemisphere) and three metadata objects (CoreMetadata, StructMetadata, and Processing_Facility) in 32 bit signed integer format.
Ancillary Data
There are two ancillary text files (.qa and .ph) included with each day of data. The .qa text file provides a quality assessment summary. The .ph text file provides a list of the input data files.
Parameter Naming Convention
Table 3 explains the parameter name variable values using the parameter convention example below.
Example parameter convention: SI_6km_HE_PARAM_TIME
| Variable | Values |
|---|---|
SI |
Indicates sea ice. |
6km |
Indicates a nominal spatial resolution of 6 km. |
HE |
Indicates the observation hemisphere; NH: Northern Hemisphere, SH Southern Hemisphere. |
PARAM |
Indicates the measured parameter; 6 GHz, 10 GHz, 18 GHz Tbs, 23 GHz Tbs, 36 GHz Tbs, and 89 GHz Tbs. Brightness Temperature parameters also include a polarization identifier; V: Vertical and H: Horizontal. |
TIME |
Indicates the observation time period; ASC: 12 hour ascending orbit, DSC: 12 hour decending orbit, DAY: Full orbit daily average |
Example parameter name: SI_6km_NH_89H_ASC
File Naming Convention
Table 4 explains the file name variable values using the file name convention example below.
Example file convention: AMSR_U2_L3_SeaIce6km_X##_yyyymmdd.he5
| Variable | Description |
|---|---|
| AMSR | Advanced Microwave Sounding Radiometer |
| U | Unified |
| 2 | AMSR2 |
| L3 | Level 3 |
X |
Product Maturity Code (Refer to Table 5) |
## |
File version number |
yyyy |
Four-digit year |
mm |
Two-digit month |
dd |
Two-digit day |
|
Hierarchical Data Format (HDF-EOS5) |
Example file name: AMSR_U2_L3_SeaIce6km_B02_20180509.he5
Table 5 provides the meaning for the product maturity code variable values.
| Variables | Description |
|---|---|
| B | Beta: indicates a developing algorithm with updates anticipated. |
| T | Transitional: period between Beta and Validated when the product is past the beta stage, but not quite ready for validation while the algorithm matures and stabilizes. |
| V | Validated: products are upgraded to Validated once the algorithm is verified by the algorithm team and validated by the validation team. Validated products have an associated validation stage. Refer to Table 2 in the Naming Conventions section of the AMSR Unified Data Versions page for a description of the stages. |
File Size
The average file size for this data set is 88.3 MB.
Spatial Information
Coverage
A small gap in coverage exists at the poles due to the path of the ascending and descending orbits. Known as the pole hole, this gap is consistent for both AMSR2 and AMSR-E data sets. For additional information see the AMSR-E Pole Hole page.
Resolution
The nominal spatial resolution of the 89.0 GHz brightness temperature polar grids is 6.25 km. However, because the polar grids are not equal area, the actual resolution varies by latitude.
Geolocation
Tables 6 and 9 provide projection and grid details for this data set.
| Northern Hemisphere | Southern Hemisphere | |
| Geographic coordinate system | Unspecified (Based on Hughes 1980 ellipsoid) | Unspecified (Based on Hughes 1980 ellipsoid) |
| Projected coordinate system | NSIDC Sea Ice Polar Stereographic North | NSIDC Sea Ice Polar Stereographic South |
| Longitude of true origin | 0 | 0 |
| Latitude of true origin | 70° N | 70° S |
| Scale factor at longitude of true origin | 1 | 1 |
| Datum | Unspecified (Based on Hughes 1980 ellipsoid) | Unspecified (Based on Hughes 1980 ellipsoid) |
| Ellipsoid/spheroid | Hughes 1980 | Hughes 1980 |
| Units | Meter | Meter |
| False easting | 0 | 0 |
| False northing | 0 | 0 |
| EPSG code | 3411 | 3412 |
| PROJ4 string |
+proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6356889.449 +units=m +no_defs |
+proj=stere +lat_0=-90 +lat_ts=-70 +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6356889.449 +units=m +no_defs |
| Reference | http://epsg.io/3411 | http://epsg.io/3412 |
| Northern Hemisphere | Southern Hemisphere | |
| Grid cell size (x, y pixel dimensions) | 6.25 km | 6.25 km |
| Number of rows | 1792 | 1328 |
| Number of columns | 1216 | 1264 |
| Geolocated lower left point in grid | -3850 E, -5350 S | -3950 E, -3950 S |
| Nominal gridded resolution | 6.25 km | 6.25 km |
| ulxmap – x-axis map coordinate of the center of the upper-left pixel (XLLCORNER for ASCII data) | -3850 | -3950 |
| ulymap – y-axis map coordinate of the center of the upper-left pixel (YLLCORNER for ASCII data) | 5850 | 4350 |
The origin of each x, y grid is the pole. Tables 7 and 8 show the approximate outer boundaries for the Arctic and Antarctic grids. Corner points are listed starting from the upper left corner and progress clockwise. Interim rows define boundary midpoints.
|
X (km) |
Y (km) |
Latitude (deg) |
Longitude (deg) |
Pixel Location |
|---|---|---|---|---|
| -3850 | 5850 | 30.98 | 168.35 | corner |
| 0 | 5850 | 39.43 | 135.00 | midpoint |
| 3750 | 5850 | 31.37 | 102.34 | corner |
| 3750 | 0 | 56.35 | 45.00 | midpoint |
| 3750 | -5350 | 34.35 | 350.03 | corner |
| 0 | -5350 | 43.28 | 315.00 | midpoint |
| -3850 | -5350 | 33.92 | 279.26 | corner |
| -3850 | 0 | 55.50 | 225.00 | midpoint |
|
X (km) |
Y (km) |
Latitude (deg) |
Longitude (deg) |
Pixel Location |
|---|---|---|---|---|
| -3950 | 4350 | -39.23 | 317.76 | corner |
| 0 | 4350 | -51.32 | 0.00 | midpoint |
| 3950 | 4350 | -39.23 | 42.24 | corner |
| 3950 | 0 | -54.66 | 90.00 | midpoint |
| 3950 | -3950 | -41.45 | 135.00 | corner |
| 0 | -3950 | -54.66 | 180.00 | midpoint |
| -3950 | -3950 | -41.45 | 225.00 | corner |
| -3950 | 0 | -54.66 | 270.00 | midpoint |
Geolocation Tools
NSIDC provides geolocation tools for polar stereographic data sets. The first two tools in the list below enable users to obtain latitude/longitude coordinates from (i,j) oordinates and vice versa. The last tool in the list enables users to identify pixel areas.
- psn06lats_v3.dat and pss06lats_v3.dat
- psn06lons_v3.dat and pss06lons_v3.dat
- psn6area_v3.dat and pss6area_v3.dat
Land Masks
A 6.25 km Northern Hemisphere land mask (amsr_gsfc_6n.hdf) and a 6.25 km Southern Hemisphere land mask (amsr_nic_6s.hdf) are available for use with these data.
Temporal Information
Coverage
02 July 2012 to the present.
Resolution
Brightness temperatures are provided in three daily-averaged composites: daily-averaged ascending orbits, daily-averaged descending orbits and a daily average of all orbits.
Sample Data Images
AMSR_2_L3_SeaIce6km_P00_20160705_N_89V.png
AMSR_2_L3_SeaIce6km_P00_20160705_S_89V.png
Data Acquisition and Processing
Acquisition
Source
This product uses the JAXA AMSR2 Level-1R input Tb observations that are calibrated (unified) across the JAXA AMSR-E and AMSR2 Level-1R products. Note that the AMSR-E products at NSIDC currently only use the Level-2A Tb observations provided by Remote Sensing Systems. In the future, AMSR-E Tb observations may be reprocessed with the unified JAXA Level-1R Tb observations and archived at NSIDC.
The Level-1R input data consist of resampled brightness temperatures. The brightness temperature sensor footprints (instantaneous fields of view) vary with frequency. The resampling remaps the brightness temperatures to sets of consistent footprint sizes using a Backus-Gilbert method. Each resampled set corresponds to the footprint of one frequency and contains that frequency plus all higher-resolution frequencies. Therefore, the number of channels in each resampled set of brightness temperatures varies. In the AU_SI6 product, only 89 GHz data is included, so there is only one resampled set of brightness temperatures. See JAXA Level 1R documentation or Maeda et al. (2016) for more information.
Processing
Processing Steps
Swath data from the 89 GHz channel are mapped onto the 6.25 km polar stereographic grid by converting the geodetic latitude and longitude for the center of each scene station, such as the observation footprint, into AMSR2 map grid coordinates. Scene station map grid coordinates determine grid cell assignments. Observations that fall outside the AMSR2 polar grid are ignored. For each grid cell, brightness temperatures observed over a 24-hour period (midnight to midnight GMT) are summed and then divided by the total number of observations to obtain a daily-averaged brightness temperature value. If no observations fall within a grid cell for a given day, the average brightness temperature is labeled 'missing'. The 24-hour averaging is done three ways: for all ascending orbits; all descending orbits; and a daily average of all orbits.
The daily average is not simply an average of ascending and descending orbits, because a given pixel could have, for example, three measurements from ascending orbits and two from descending orbits. Instead, the algorithm computes the daily average for that grid cell from daily ascending and descending averages. For example, if A = ascending and B = descending:
((A1 + A2)/2 + (B1 + B2 + B3)/3)/2 (Equation 1)
However, this approach biases daytime (ascending) orbits over nighttime (descending) orbits.
Quality
Assessment
Each HDF-EOS5 data file contains core metadata with quality assessment (QA) metadata flags. These flags are set by the operational processing code run by the AMSR Science Investigator-led Processing System (SIPS) prior to delivery to NSIDC. A separate metadata file in XML format is also delivered to NSIDC with the HDF-EOS5 file. This file contains the same quality assessment (QA) metadata flags as the core metadata contained in the HDF-EOS5 file. Three levels of QA are applied to AMSR2 files: automatic, operational, and science. Please note that if a granule passes automatic QA and operational QA, the granule is forwarded to NSIDC for archive and distribution. If not, the issue is resolved and the granule is reprocessed. Science QA is performed automatically during nominal processing but only reviewed closely after the fact in conjunction with questions that arise post-processing.
Automatic QA
Out-of-bounds Level-1R brightness temperatures are screened out before brightness temperatures are interpolated to the 6.25 km grid.
Operational QA
AMSR2 L1R data are subject to operational QA by JAXA prior to arriving at the AMSR SIPS for processing to higher level products. Operational QA varies by product, but it typically checks for the following criteria in a given file (Conway 2002):
- File is correctly named and sized
- File contains all expected elements
- File is in the expected format
- Required EOS fields of time, latitude, and longitude are present and populated
- Structural metadata are correct and complete
- File is not a duplicate
- HDF-EOS5 version number is provided in the global attributes
- Correct number of input files were available and processed
Science QA
In the SIPS environment, as part of the processing code, the science QA includes checking the maximum and minimum variable values, and percent of missing data and out-of-bounds data per variable value. At the Science Computing Facility (SCF), co-located with the SIPS, post-processing science QA involves reviewing the operational QA files and browse images, and performing the following additional QA procedures (Conway 2002):
- Comparisons with historical data
- Detection of errors in geolocation
- Verification of calibration data
- Detection of trends in calibration data
- Detection of large scatter among data points that should be consistent.
Several tools have been developed to aid in the QA process of the Level 3 AMSR2 products. The AMSR SIPS provides software that creates a QA browse image in Portable Network Graphics (PNG) format that can be used for visual QA. The team lead SCF (TLSCF) provides metadata and QA software specific to each product that generate the metadata files discussed above and a QA summary report in text format. The products of these tools are provided to NSIDC along with each data granule.
Accuracy and Precision
Refer to the Algorithm Theoretical Basis Document for information about data used to check the accuracy and precision of AMSR2 observations.
Anomalies
Refer to the AMSR2 LANCE Anomalies Page for information regarding data anomalies or gaps in coverage.
Instrument Description
For a detailed description of the AMSR2 instrument, refer to the AMSR2 Channel Specification and Products page.
Software and Tools
For general tools that work with HDF-EOS data, see the NSIDC HDF-EOS web page.
Contacts and Acknowledgments
Josefino Comiso
Laboratory for Hydrospheric Processes
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Thorsten Markus
Laboratory for Hydrospheric Processes
NASA Goddard Space Flight Center
Greenbelt, MD 20771
References
Meier, W.N., and A. Ivanoff, 2017. Intercalibration of AMSR2 NASA Team 2 algorithm sea ice concentrations with AMSR-E slow rotation data, IEEE J. Spec. Topics Appl. Earth Obs. & Rem. Sens., 10(8), doi:10.1109/JSTARS.2017.2719624.
Comiso, J. C. 2009. Enhanced sea ice concentration and ice extent from AMSR-E Data. J. Remote Sensing Soc. of Japan 29(1): 199-215.
Markus, T., and D. J. Cavalieri. 2009. "The AMSR-E NT2 sea ice concentration algorithm: its basis and implementation." Journal of The Remote Sensing Society of Japan, 29 (1): 216-225
Comiso, J., D. Cavalieri, and T. Markus. 2003. Sea Ice Concentration, Ice Temperature, and Snow Depth using AMSR-E data. IEEE Transactions on Geoscience and Remote Sensing 41(2): 243-252.
Markus, T. and D. Cavalieri. 2000. An Enhancement of the NASA Team Sea Ice Algorithm. IEEE Transactions on Geoscience and Remote Sensing 38: 1387-1398.
