Alaska Satellite Facility
Delivering Remote Sensing Data Since 1991
Synthetic aperture radar (SAR) RTC images processed
Synthetic aperture radar (SAR) RTC scenes

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). 


Radiometric Terrain Correction

Click for Product Guide


ASF's RTC 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.


RTC Products

Synthetic aperture radar (SAR) PALSAR Grand Canyon

These two images of part of the Grand Canyon are processed from the 
same PALSAR data. The image on the left is uncorrected. The image on the
right is terrain 
corrected. In the uncorrected image, the sides of the canyon
appear to be stretched on one side and 
compressed on the other side.
Click to enlarge. ASF DAAC 2014; Includes Material © JAXA/METI 2008.

Both a high (12.5m) and a low (30m) resolution product have been produced for all project areas.

The high-resolution product bundle includes:

  • Gamma naught power, floating point
  • UTM GeoTIFF 12.5m
  • GeoTIFF Incidence Angle Map, 32 bit float radians 
  • DEM INT16 GeoTIFF 12.5m
  • Geo-JPEG browse 1000 x 1000 (color for FBD & PLR)
  • ISO 19115 compliant metadata
  • KMZ with 30m overlay

The low-resolution bundle includes:

  • Gamma naught power, floating point, UTM GeoTIFF 30m
  • Layover/Shadow mask byte GeoTIFF - 30m
  • GeoTIFF Incidence Angle Map, 32 bit float radians
  • DEM INT16 GeoTIFF 90m
  • Geo-JPEG browse 1000 x 1000 (color for FBD & PLR)
  • ISO 19115 compliant metadata
  • KMZ with 30m overlay

More information is available in the RTC Product Guide and in the ATBD (algorithm) information.
DEM elevation information is in the FAQs.


Video tutorial: How to download DEMs. Cómo descargar DEMs

Video created by Géo Tech


Synthetic aperture radar (SAR) PALSAR before and after correction

PALSAR images of hills in Fairbanks, Alaska, before and after
radiometric correction. The correction adjusts the values of the pixels
to show only the properties of the land surface. This is a sigma naught image.
Actual products are gamma naught. ASF DAAC 2014; Includes Material
© JAXA/METI 2008.

Image Corrections

Radiometric Correction

Synthetic aperture radar (SAR)correction PALSAR before and after correction

PALSAR images of hills in Fairbanks, Alaska, before and after terrain 
correction. The correction involves moving pixels, effectively sliding
the hills into the correct geometry. This is a sigma naught image.
Actual products are gamma naught. ASF DAAC 2014; Includes
Material © JAXA/METI 2008.

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 images of the Rocky Mountains before and after terrain 
correction. Extreme layover is corrected as the mountains 
are made to "stand up." ASF DAAC 2014; Includes Material 
© JAXA/METI 2007.


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.

Synthetic aperture radar (SAR) uncorrected PALSAR and Landsat 8

PALSAR (L1.5 uncorrected) and Landsat 8 fusion. Note the incoherent appearance.
Click for larger images. ASF DAAC 2014; Includes Material 
© JAXA/METI 2009.

Synthetic aperture radar (SAR) uncorrected PALSAR and Landsat 8

PALSAR RTC and Landsat 8 fusion. Note the close match between images.
Click for larger images. ASF DAAC 2014; Includes Material 
© JAXA/METI 2009.

Get SAR Data

Get SAR Data

Select and download SAR data online using Vertex.

Use the ASF API for downloading SAR data via a command line.