ALOS Processing Options

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This page describes specific processing options for Geoscience Australia ALOS data. If you are unfamiliar with the generic processing options, it is recommended that you first read the Optical Data Processing Options.

If you already understand the processing options below, you may be interested in the ALOS Geometric and Radiometric Specifications.

ALOS processing levels

The various processing levels for ALOS data are described below. Links are provided also to the various Map Projection Options for Optical Image Products and Geometric Correction and Resampling of Data.

The differences between coordinate systems used for all ALOS products is the World Geodetic System 1984 (WGS84). This is due to a standardised worldwide processing system for ALOS.

For a particular ALOS sensor, pixel sizes remain unchanged for each processing level. For example, a PRISM triplet scene product has a pixel size of 10 metres for both path image and map oriented image processing level. This is unlike Landsat products which have different pixel sizes for path image and map oriented image.

PRISM and AVNIR-2

Processing level Description
Standard processing levels (suitable for input into most image processing software)
PRISM Wide Swath
ortho-corrected image (70 x 35KM)

Map oriented with systematic geometric corrections refined with the use of GCPs and the best DEM available to Geoscience Australia. (Note potential limitations to spatial positional accuracy.)

Map Projection Options for Optical Image Products: UTM
Geometric Correction and Resampling of Data options: NN, BL, CC

Map oriented image
(Level 1B2-G)

Image pixels are aligned to the map grid. (Radiometric calibration and geometric correction coefficients applied - rotation has been applied to make 'north up'.)
Map Projection Options for Optical Image Products: UTM
Geometric Correction and Resampling of Data options: NN, BL, CC

Note that this is not an ortho-corrected product.

Path image
(Level 1B2-R)
Image pixels are aligned to the satellite path. (Radiometric calibration and geometric correction coefficients applied - the image requires the user to apply a rotation factor to make 'north up'.)
Map Projection Options for Optical Image Products: UTM
Geometric Correction and Resampling of Data options: NN, BL, CC
Non-standard processing level (not suitable for most customers)
Raw image data
(Level 1B1)
As for raw image, plus radiometric correction.
Raw image
(Level 1A)
Uncompressed, reconstructed digital counts with radiometric and geometric calibration coefficients (appended but not applied).

Please note that orthocorrected ALOS products are not available at this time. We are investigating procedures to provide orthocorrected images in the future.

PALSAR

Processing level Description
Standard processing levels (suitable for input into most image processing software)
Map oriented image
(Level 1.5-G)
Multi-look processed image projected to map coordinates.
Image pixels aligned to the map grid.
Map projection options:
  • Fine beam (high resolution) mode: UTM
  • ScanSAR: UTM, LCC (GALCC)
  • Direct downlink: UTM
Path image
(Level 1.5-R)
Multi-look processed image projected to map coordinates.
Image pixels aligned to the satellite path.
Map projection options:
  • Fine beam (high resolution) mode: UTM
  • ScanSAR: UTM, LCC (GALCC)
  • Direct downlink: UTM
Non-standard processing level (not suitable for most customers)
Single look complex
(L1.1)
Complex data on slant range after range and azimuth compression processing.
Can be processed for high resolution mode, Polarimetric mode or direct downlink mode data.
Note this level is not available for SCANSAR
Raw data
(L1.0)
Reconstructed, unprocessed signal data with radiometric and geometric calibration coefficients (appended but not applied).
Can be acquired in high resolution mode, Scan SAR mode, Polarimetric mode or direct downlink mode.

Pixel sizes

The pixel sizes quoted for the ALOS Satellite characteristics apply to Nadir viewing by PRISM and to the default viewing angle for PALSAR. AVNIR-2 products processed after August 2007, will have a pixel size of 10 metres for all viewing angles.

Shifted scenes (framing your product)

Our products are extracted from a continuous swath of data collected by the orbiting satellite. Products can be framed from this swath in a variety of ways. For the purposes of product generation and delivery, each swath is normally divided into nominal scenes.

PRISM

There is a small amount of overlap necessary between each nominal scene along the swath such that nominal scene-centres are less than 35 kilometres apart for PRISM triplet mode.

PRISM nadir scenes

For an individual nadir scene from the ALOS PRISM triplet mode or wide swath mode, you may frame your product between the nominal centres in increments of 20% along the satellite track. The diagram below shows the 20% scene shifts which are possible and how they are labelled. Scene shifts can be labelled 0 (no shift), -2, -1, 1 or 2. If you require a scene shift, one of these numbers needs to be specified at the time of ordering. The diagram below shows a nominally framed scene in black (0 shift) and a shifted scene of +1 (=20%) in red, with the shifted scene centre represented by a red cross. A PRISM scene shift of +1 equates to a ground distance of approximately seven kilometres.

DIAGRAM of a PRISM triplet mode shifted scene

DIAGRAM of a PRISM triplet mode shifted scene

PRISM triplet scenes

A set of PRISM triplet scenes also may be ordered in triplet mode (i.e. forward, nadir and backward scenes). Note that our Earth Observation Catalogue displays only the nadir scene from a triplet set. In rare cases, there may be no associated forward or backward scene, which will be indicated in the metadata for that scene.

No scene shift is possible when ordering a triplet set, two scenes from a triplet set or an individual forward/backward scene. This allows us to optimise the overlap of the forward and backward scene with the nadir scene in the catalogue. Note that this overlap is optimised, but not complete.

AVNIR-2

There is a small amount of overlap necessary between each nominal scene along the swath such that nominal scene centres are less than 70 kilometres apart for AVNIR-2.

For AVNIR-2 the product may be framed in increments of 10% along the satellite track. Scene shifts can be -5, -4, -3, -2, -1, 0, +1, +2, +3 or +4, where each unit represents an approximate 10% shift, or about seven kilometres on the ground. The concept is similar to that described in the diagram above for PRISM. To order a shifted scene, the nominal scene centre coordinates still need to be quoted in addition to the required shift.

The Geoscience Australia Earth Observation Catalogue will have a tool in the future to help display the ground coverage of specified scene shifts.

PRISM and AVNIR-2 Scene Shifts

If a shifted scene is specified for ordering, you must ensure that the altered framing covers an area that:

  • is physically in the catalogue
  • has acceptable cloud cover for your requirements.

For example, if a nominal scene is shifted south along the satellite swath, it should be ensured that the next nominal scene to the south exists and that it has acceptable cloud cover in the northern portion forming part of the shifted product.

PALSAR

There is a small amount of overlap necessary between each PALSAR nominal scene such that nominal scene centres are a little less than 70 kilometres apart (more for ScanSAR) along the swath. If you wish to frame your product between these nominal centres you may do so in increments of approximately 10% along the satellite path.

As described above for PRISM and AVNIR-2 product framing, you can frame your PALSAR products along track by specifying scene shifts of -5, -4, -3, -2, -1, 0, +1, +2, +3 or +4.

To order a shifted scene, the nominal scene centre coordinates need to be quoted in addition to the required shift. The Geoscience Australia Earth Observation Catalogue will have a tool in the future to help display the ground coverage of specified scene shifts. If a shifted scene is ordered, you must ensure that the altered framing covers an area for which there is data in the catalogue.

Data format

ALOS satellite data is provided in formats suitable for image processing software. It is not suitable for viewing with standard office and home-based software.

PRISM and AVNIR-2 PRISM Wide Swath PALSAR
Path oriented Map oriented ortho-corrected Image All data
CEOS format only* CEOS format*
OR
GeoTIFF
GeoTIFF CEOS format only*

*CEOS formats for Geoscience Australia ALOS data also include header files for ER Mapper and ENVI image processing software.

We will consider adding additional text header files to facilitate direct read of ALOS products in other image processing packages. Please contact us with your request.

More details are available from ALOS Product Descriptions and Formats.

Topic contact: earth.observation@ga.gov.au Last updated: August 27, 2012