Alos Palsar
PALSAR was one of three instruments on the Advanced Land Observing Satellite-1 (ALOS), also known as DAICHI, developed to contribute to the fields of mapping, precise regional land-coverage observation, disaster monitoring, and resource surveying. ALOS was a mission of the Japan Aerospace Exploration Agency (JAXA).
Alaska Satellite Facility’s Radiometric Terrain Correction Project (RTC)
Creation of RTC products is a project of ASF that makes SAR data accessible to a broader community of users. The project corrects synthetic aperture radar (SAR) geometry and radiometry, and presents the data in the GIS-friendly GeoTIFF format. Data included in the RTC project are Fine Beam and Polarimetric scenes in all global land areas except Antarctica, Greenland, Iceland, and northern Eurasia.
ALOS Phased Array type L-band Synthetic Aperture Radar
| Fine Resolution | ScanSAR | Polarimetric | ||
|---|---|---|---|---|
| Beam Mode | FBS, DSN | FBD | WB1, WB2 | PLR |
| Center Frequency | L-Band (1.27 GHz) | |||
| Polarization | HH or VV | HH+HV or VV+VH | HH or VV | HH+HV+VV+VH |
| Spatial Resolution | 10 m | 20 m | 100 m | 30 m |
| Swath Width | 70 km | 70 km | 250-350 km | 30 km |
| Off-Nadir Angle | 34.3° (default) | 27.1° (default) | 21.5° (default) | |
PALSAR cannot observe the areas beyond 87.8 degrees north latitude and 75.9 degrees south latitude when the off-nadir angle is 41.5 degrees.
Read more on the JAXA website.
PALSAR Technical Specs — Beam Modes
PALSAR has two fine beam modes: single polarization (FBS) and dual polarization (FBD), as well as quad polarization, also known as polarimetric mode (PLR). ScanSAR wide beam (WB1, WB2) operates with a considerable loss of resolution. See table below.
From 2006 to 2011, PALSAR’s L-band synthetic aperture radar (SAR) yielded detailed, all-weather, day-and-night observation, as well as repeat-pass interferometry. PALSAR data are from multiple observation modes with variable polarization, resolution, swath width, and off-nadir angle.
PALSAR was one of three instruments on the Advanced Land Observing Satellite-1 (ALOS), also known as DAICHI, developed to contribute to the fields of mapping, precise regional land-coverage observation, disaster monitoring, and resource surveying. ALOS was a mission of the Japan Aerospace Exploration Agency (JAXA).
ALOS L1.5 FBS Coverage Map
ALOS L1.5 FBD Coverage Map
ALOS L1.5 FBS Coverage Map
ALOS L1.5 FBD Coverage Map
ALOS L1.5 Wide Beam Coverage Map
ALOS L1.5 Polarimetric Coverage Map
Additional coverage maps from the ALOS data collection.
PALSAR
| Name | Description |
|---|---|
| ALOS Data Users Handbook, 2008 | Overview of the ALOS Project and related technological information on satellites and land systems |
| ALOS User Guide | Overview, products, product format, operations |
| PALSAR Product Format | Detailed L1.1 and L1.5 product format description |
| PALSAR Product Format (zip file downloads) | Detailed L1.0 product format description |
Radiometrically Terrain-Corrected (RTC)
| Name | Description |
|---|---|
| RTC Product Guide, 2015 | Guide for radiometrically terrain-corrected products. |
| RTC Product Specification, 2014 | This product format specification defines standard terrain-corrected products generated at ASF. It contains the definition for the ISO-compliant XML metadata. |
| RTC ATBD, 2015 | Algorithm theoretical basis document: Provides the theoretical background of the algorithms and processing flows used for the generation of terrain-corrected products processed by ASF. |
Software Tools
| Name | Description |
|---|---|
| MapReady, ASF | Terrain correct, geocode, and apply polarimetric decompositions to multi-pol SAR data |
| Convert to Vector, ASF | Transform point or scene information to formats compatible with Google Earth, GIS, and more |
| SAR Training Processor, ASF | Learn SAR processing |
| Bulk Download, ASF | Bulk download from the ASF datapool via Metalink files |
| Other Software Tools | Access a variety of tools for viewing, analyzing, and processing radar data |
GIS Platforms
RTC GeoTIFF products are readily visualized in GIS programs such as ArcGIS or QGIS.
| Name | Description |
|---|---|
| QGIS: open source | Windows, Mac, Linux, BSD |
| ArcGIS: commercial software | Windows, Linux |
Processors
PALSAR Processor versions used to process data at ASF
| Processing Dates | Processor Version | JAXA Calibration Result as of (MM-DD-YYYY) |
|---|---|---|
| April 18, 2007- April 26, 2007 | 3.00 | 10-23-2006 3-29-2007 |
| April 27, 2007- March 17, 2008 | 4.00 | 3-29-2007 9-28-2007 |
| March 18, 2008 – June 12, 2008 | 4.03 | 9-28-2007 |
| June 13, 2008 – February 3, 2009 | 5.00 | 9-28-2007 |
| February 4, 2008 – ? | 5.04 | 9-28-2007 7-1-2009 |
| September, 2013 | 6.07 | 9-6-2011 |
Optical Processor versions used to process data at ASF
| Processing Dates | Processor Version | JAXA Calibration Result as of (MM-DD-YYYY) |
|---|---|---|
| April 18, 2007- April 26, 2007 | 3.00 | 10-23-2006 3-29-2007 |
| April 27, 2007- March 30, 2009 | 4.01 | 3-29-2007 9-28-2007 |
| March 31, 2009 – February 3, 2010 | 5.02 | 9-28-07 7-1-2009 |
| February 4, 2010 – January 18, 2011 | 5.09 | 7-1-2009 |
| January 18, 2011 – Present | 6.03 | 7-1-2009 |
How to Obtain PALSAR Data
Researchers can download open-access ALOS PALSAR data from the NASA-sponsored ASF DAAC.
Product Type Format Open Access L1.0 Unprocessed/raw n/a Find Data L1.5 Georeferenced amplitude image CEOS Find Data RTC Radiometrically and terrain-corrected geocoded GeoTIFF image GeoTIFF Find Data
Note 1: L1.0 and L1.5 products may have originated from older JAXA processor versions.
Note 2: Users may request L1.1 data – if not already available through Vertex or the ASF API – by contacting our User Support Office, [email protected]. Please provide a list of the granule names you wish to have processed.
L1.1 processing is not possible for data acquired in ScanSAR beam mode (WB1 and WB2).
RTC Products
ASF has produced products at both 12.5-m and 30-m resolutions for the areas indicated in the map.
The product package includes the following contents:
Radiometric Terrain Corrected GeoTIFF file for each polarization available
- Pixel values are gamma nought power in 32-bit floating point format
- Pixel spacing is 12.5 m for high-resolution (RT1) and 30 m for low-resolution (RT2) products
Incidence Angle GeoTIFF, indicating the angle in radians for each pixel
- Pixel spacing is the same as the RTC GeoTIFF in the package
Layover/Shadow GeoTIFF, indicating where processing was impacted by layover or shadow
- Pixel spacing is the same as the RTC GeoTIFF in the package
- The DEM used for RTC processing in GeoTIFF format
Best resolution SRTM or NED source DEM available, with geoid correction applied
- Pixel spacing is the same as the RTC GeoTIFF in the package
Technical information is available in the RTC Product Guide and the ATBD (algorithm) information
- Browse image in GeoJPEG format
- 1000 x 1000 pixels
Color images available when multiple polarizations are available (FBD and PLR products)
- Metadata in ISO 19115 format (xml file)
- KMZ file with 30-m overlay
Note: More information on the DEMs used for RTC processing can be found in the PALSAR RTC DEM Information section.
ALOS PALSAR & RTC Standard Product License Agreement
The Alaska Satellite Facility (ASF) grants the End User use of Advanced Land Observing Satellite (ALOS) PALSAR data if the End User accepts and agrees to the following ALOS PALSAR Standard Product End User License Agreement. The End User will be deemed to have accepted and agreed to the terms and conditions if the End User starts using ALOS PALSAR data including but not limited to downloading, installing, manipulation or other action.
Section 1 Definitions
1. “End User” means the person, legal business entity, public entity or any other legal entity who obtains the Product and is considered to have accepted this End User License Agreement. In the case of a public entity, the End User is deemed to be only the part, division, etc. of the public entity located at the address to which the Product is supplied, unless otherwise agreed upon by ASF in writing and in advance.
Standard Product – Level 1 Data (CEOS format) PALSAR Level 1.0, 1.1, 1.5
Derivative Work Product – A processed product using the Standard Product which retains the original pixel structure and can be converted back to the original data or a processed product that does not retain the original pixel structure and cannot be converted back to the original data , with the exception of value-added products
Value Added Product (VAP) – A modified Standard or Derivative Work Product with high-level processing that cannot be converted back to the original product. The high-level processing includes data analysis or combining multiple-satellite data, image processing based on external information, and physical quantity conversion.
2. “Product” means any ALOS satellite data product supplied by ASF. Product is classified as standard product, Derivative-work Product and Value Added Product (VAP). Definition of the three product types is shown below.
3. “JAXA” means the Japan Aerospace Exploration Agency.
4. “METI” means the Japanese Ministry of Economy, Trade, and Industry.
5. “Related Parties” means the parties that have been involved in the creation, production, distribution or delivery of the Product.
Section 2 Permitted Uses
1. The End User shall utilize the Product for peaceful purposes only.
2. The End User may redistribute the Product provided the data source is attributed to JAXA/METI.
Section 3 Prohibited Uses
1. The End User shall not use the Product other than for peaceful purposes.
2. The End User shall not delete, obscure, remove or alter any copyright notice that is contained in or appears on the Product.
Section 4 Intellectual Property Right and Copyright Notice
1. The End User confirms that JAXA and METI own all intellectual property rights, including copyrights, for ALOS PALSAR Standard and Derivative-work products.
2. The End User owns all intellectual property rights, including copyrights, which result from the End User’s act of interpretation, adaptation, authorship or any other work on the Standard Product resulting in the creation of a VAP. All VAP products must be accompanied with the copyright notice.
3. The End User agrees that any embodiment of the Product permitted under this agreement shall contain the following copyright notice. The copyright notice shall be prominently displayed and the [Year] field correctly filled with a numerical value corresponding to the year of raw data acquisition.
Copyright Notice
Standard Product – ©JAXA,METI [Year] Derivative Work Product – ©JAXA,METI [Year] Value Added Product – Includes Material ©JAXA,METI [Year]
Section 5 Limited Warranty – Disclaimer
1. Neither ASF nor the Related Parties, if any, warrants that the Product is free of bugs, errors, defects or omissions.
2. The Product is provided as is with no warranty of merchantability or fitness for a particular purpose.
3. ASF and the Related Parties shall have no liability to the End User for any damage suffered by the End User or any third party, as a result of using ALOS PALSAR products. This damage is including but not limited to consequential loss and lost earnings.
Section 6 Modification of this Agreement
ASF reserves the right to modify this agreement if necessary and the modified agreement will govern. In the case of modification ASF will announce on ASF internet site.
Section 7 Governing Law and Jurisdiction
This End User License Agreement shall be governed by the laws of the United States of America.
ALOS PALSAR RTC Product License Agreement
The Alaska Satellite Facility (ASF) grants the End User use of Radiometrically Terrain Corrected (RTC) Advanced Land Observing Satellite (ALOS) PALSAR data if the End User accepts and agrees to the following ALOS PALSAR RTC End User License Agreement. The End User will be deemed to have accepted and agreed to the terms and conditions if the End User starts using ALOS PALSAR RTC data including but not limited to downloading, installing, manipulation or other action.
Section 1 Definitions
1. “End User” means the person, legal business entity, public entity or any other legal entity who obtains the Product and is considered to have accepted this End User License Agreement. In the case of a public entity, the End User is deemed to be only the part, division, etc. of the public entity located at the address to which the Product is supplied, unless otherwise agreed upon by ASF in writing and in advance.
Value Added Product (VAP) – A modified Standard or Derivative Work Product with high-level processing that cannot be converted back to the original product. The high-level processing includes data analysis or combining multiple-satellite data, image processing based on external information, and physical quantity conversion.
2. “Product” means any ALOS RTC satellite data product supplied by ASF. Product is classified as Value Added Product (VAP). Definition of the product types is shown below.
3. “JAXA” means the Japan Aerospace Exploration Agency.
4. “METI” means the Japanese Ministry of Economy, Trade, and Industry.
5. “Related Parties” means the parties that have been involved in the creation, production, distribution or delivery of the Product.
Section 2 Permitted Uses
These data are provided in accordance with NASA’s free and open data policy. There are no restrictions on their use.
Section 3 Prohibited Uses
1. The End User shall not delete, obscure, remove or alter any copyright notice that is contained in or appears on the Product.
Section 4 Intellectual Property Right and Copyright Notice
1. The End user confirms that NASA retains the copyright to the ALOS PALSAR RTC products, and that JAXA/METI retain the copyright to the original data from which the Product was derived.
2. The End User owns all intellectual property rights, including copyrights, which result from the End User’s act of interpretation, adaptation, authorship or any other work on the Product resulting in the creation of another VAP. All VAP products must be accompanied with the appropriate copyright notice.
3. The End User agrees that any embodiment of the Product permitted under this agreement shall contain the following copyright notice. The copyright notice shall be prominently displayed and the [Year] field correctly filled with a numerical value corresponding to the year of raw data acquisition.
Copyright Notice for ALOS PALSAR RTC: © NASA [Year], Includes Material © JAXA, METI [Year]
Section 5 Limited Warranty – Disclaimer
1. Neither ASF nor the Related Parties, if any, warrants that the Product is free of bugs, errors, defects or omissions.
2. The Product is provided as is with no warranty of merchantability or fitness for a particular purpose.
3. ASF and the Related Parties shall have no liability to the End User for any damage suffered by the End User or any third party, as a result of using ALOS PALSAR RTC products. This damage is including but not limited to consequential loss and lost earnings.
Section 6 Modification of this Agreement
ASF reserves the right to modify this agreement if necessary and the modified agreement will govern. In the case of modification ASF will announce on ASF internet site.
Section 7 Governing Law and Jurisdiction
This End User License Agreement shall be governed by the laws of the United States of America.
ASF's ALOS PALSAR Radiometric Terrain Correction Project
ASF’s Radiometric Terrain Correction Project
Creation of radiometrically terrain corrected (RTC) products is a project of the Alaska Satellite Facility that makes SAR data accessible to a broader community of users. The project corrects synthetic aperture radar (SAR) geometry and radiometry, and presents the data in the GIS-friendly GeoTIFF format.
Release of new ALOS PALSAR RTC products commenced October 2014 and was completed a year later. Data included in the RTC project are Fine Beam and Polarimetric scenes in all global land areas except Antarctica, Greenland, Iceland, and northern Eurasia.
Extent and concentration of processed RTC scenes. PALSAR has two fine beam modes, single polarization (FBS) and dual polarization (FBD), as well as quad polarization, also known as polarimetric mode (PLR).
Image Corrections
Radiometric Correction
Radiometric correction involves removing the misleading influence of topography on backscatter values. For example, the correction eliminates bright backscatter caused by radar reflection from steep slopes, leaving only the backscatter that reveals surface characteristics such as vegetation and soil moisture.
In the image on the right, southern slopes are initially bright, northern slopes are dark. After correction the southern slopes have a more uniform appearance. Interestingly, the northern slopes stay dark. This is attributable to different vegetation types: deciduous trees on the southern slopes, and conifers such as white and black spruce on the northern slopes.
Terrain Correction
Terrain correction is the process of correcting geometric distortions that lead to geolocation errors. The distortions are induced by side-looking (rather than straight-down looking or nadir) imaging, and compounded by rugged terrain. Terrain correction moves image pixels into the proper spatial relationship with each other. Mountains that look as if they have fallen over toward the sensor are corrected in their shape and geolocation. Terrain correction in moderate topography is shown on the right, in mountainous terrain below.
Correction of geometric distortion is sometimes called orthorectification, especially for processing of optical imagery.
Radiometric Terrain Correction
Radiometric terrain correction combines both corrections to produce a superior product for science applications.
PALSAR and Landsat 8 Fusion
PALSAR and Landsat can be used as complementary or fusion products for biomass estimation, biodiversity assessment, and forest mapping and monitoring. ASF’s RTC product provides researchers an off-the-shelf match to Landsat 8, an orthorectified product.
The fusion images below demonstrate the off-the-shelf compatability between ASF’s RTC product and Landsat 8, an orthorectified product. The first image shows the incoherent appearance of the uncorrected PALSAR L1.5 image fused with Landsat 8. The second image, a fusion of RTC and Landsat 8, shows an excellent match.
PALSAR RTC DEM Information
Most DEMs are geoid-based and require a correction before they can be used for terrain correction. The DEM included with an ASF RTC product was converted from the orthometric height of the source DEM to ellipsoid height using the ASF MapReady geoid_adjust tool. This tool applies a geoid correction so that the resulting DEM relates to the ellipsoid.
The GeoidEval Utilty is a free online tool that computes the height of the geoid above the WGS84 ellipsoid at a specific location, and will show the amount of correction that was applied to the source DEM used in creating an RTC product.
About the source DEMs used for ALOS PALSAR RTC processing
The quality of an ALOS PALSAR RTC product is directly related to the quality of the digital elevation model (DEM) used in the radiometric terrain correction (RTC) process. The table below summarizes the various DEM sources and the map indicates which DEM was used in a given location.
The continental U.S., Hawaii, and parts of Alaska are covered with 1⁄3 arc-second National Elevation Dataset (NED) at a 10 m resolution. The rest of Alaska above 60 degrees northern latitude was only available at 60 m resolution with 2 arc-second NED data. The best resolution for Canada and Mexico at 30 m was provided by 1 arc-second NED. For the remaining globe, the Shuttle Radar Topography Mission (SRTM) GL1 data at 1 arc-second (30 m) resolution was used. Greenland and Antarctica were mostly covered by ice and glaciers and not suitable for terrain correction. For areas in Eurasia above 60 degrees northern latitude, no suitable DEMs were available.
DEMs used for ALOS PALSAR RTC processing
| DEM | Datum | Coverage Area | DEM Resolution | Product Resolution | Resampling Approach |
|---|---|---|---|---|---|
| NED13 | NAVD88 | CONUS, Hawaii, parts of Alaska | ~10m (1/3 arc sec) | 12.5 m | No resampling |
| 30 m | Down-sampled DEM to 30-m pixel spacing | ||||
| SRTMGL1 | EGM96 | Latitudes between 60 N and 57 S degrees | ~30 m (1 arc sec) | 12.5 m | Up-sampled 30-m mapping function to 12.5-m mapping function |
| 30 m | No resampling | ||||
| SRTMUS1 | EGM96 | CONUS, Hawaii, parts of Alaska | ~30 m (1 arc sec) | 12.5 m | Up-sampled 30-m mapping function to 12.5-m mapping function |
| 30 m | No resampling | ||||
| NED1 | NAVD88 | CONUS, Hawaii, parts of Alaska, Canada, Mexico | ~30 m (1 arc sec) | 12.5 m | Up-sampled 30-m mapping function to 12.5-m mapping function |
| 30 m | No resampling | ||||
| NED2 | NAVD88 | Alaska | ~60 m (2 arc sec) | 12.5 m | Up-sampled 30-m mapping function to 12.5-m mapping function |
| 30 m | Up-sampled DEM to 30-m pixel spacing |
The DEMs were pre-processed by ASF to a consistent raster format (GeoTIFF) from the original source formats: height (*.hgt), ESRI ArcGrid (*.adf), etc. Many of the NASA-provided DEMs were provided as orthometric heights with EGM96 vertical datum. These were converted to ellipsoid heights using the ASF MapReady tool named geoid_adjust. The pixel reference varied from the center (pixel as point) to a corner (pixel as area). The GAMMA software, used to generate the terrain-corrected products, uses pixel as area and adjusts DEM coordinates as needed. Where more than one DEM was available, the best-resolution DEM was used for processing. Complete DEM coverage from a single DEM source was required for processing to proceed.
