The Synthetic Aperture Radar (SAR) data transmitted to Earth from an Earth observation satellite are in a form unsuitable for immediate use by customers. Geoscience Australia can process the raw data in a number of ways to produce products which comply with a range of standard processing levels suitable for use by clients. In the case of SAR data from the JERS-1 (Japanese Earth Resource Satellite), our products are processed to conform to the European Space Agency (ESA) specifications and formats, with the exception of Raw Data products which conform to JAXA format specifications.
The information below has been compiled to present an overview of the processing levels available. Further detailed information on processing levels may be obtained from Geoscience Australia, while general information about SAR is available through NASA's Jet Propulsion Laboratory publication on What is Imaging Radar?
There are three basic aspects associated with processing SAR data:
At the most basic level of processing, data is not able to be interpreted as an image. An image is formed only after considerable processing of the data.
After this initial processing, the image can be oriented to the satellite path, or to a map projection.
These corrections include multi-looks (averaging of the data), incorporation of Ground Control Points and/or Digital Elevation Models as mentioned under the relevant categories below.
There is a trade-off between radiometric accuracy and spatial resolution. For example, improved radiometric accuracy resulting from an increased number of looks will result in reduced speckle with lower spatial resolution.
Data products at this level consist of minimally pre-processed raw SAR data suitable for input to another SAR processor. Such data is not able to be ingested by an image processing system and is most likely to be used by research institutes interested in full SAR data processing, or as an interchange format for other SAR ground stations. The product contains all the required auxiliary data necessary for data processing.
| Raw Data | Characteristics |
|---|---|
| Scene area (nominal) | 75km (range) × 75km (azimuth) approx. |
| Spatial Resolution | 9m range; 5m azimuth |
| Pixel depth (2 samples/pixel) | 8 bits I; 8 bits Q |
| Total product volume | ~420MBytes |
| Projection | Slant range |
| Number of looks | 1 range; 1 azimuth |
This product can be considered the foundation for all other products below, but its use requires sophisticated SAR processing software. The data are in 'slant range' which basically means that relationships between observed objects across track are based on time differences between radar pulses. This is in contrast to other processing levels in 'ground range', meaning that observed objects are spatially related to the Earth as an approximate flat image.
Single Look Complex data maintain the phase information of the data. Its primary use is for interferometry as well as for the development, calibration, testing and use of SAR algorithms used in post-processing.
| Raw Data | Characteristics |
|---|---|
| Scene area (nominal) | 75km × 75km (approx.) |
| Spatial Resolution | 9m range; 5m azimuth |
| Pixel depth | 16 bits I; 16 bits Q |
| Total product volume | ~420Mbytes |
| Projection | Slant range |
| Number of looks | 1 range; 1 azimuth |
This is a path oriented and system corrected product, being the basic product used for a variety of remote sensing applications. The European Space Agency (ESA) uses the name 'Precision Image' for this product, but we have chosen not to adopt this name due to potential confusion with other products.
This is a multilook product. The multilook process reduces the noise and results in less speckle on the image. However, there is an increase in coarseness of the spatial resolution.
| Raw Data | Characteristics |
|---|---|
| Scene area (nominal) | 75km × 75km (approx.) |
| Spatial resolution | 16m range; 14m azimuth |
| Pixel size | 12.5m × 12.5m |
| Total product volume | ~100Mbytes |
| Projection | Ground range |
| Effective No. of looks | 3 |
This is a map oriented and system corrected product. Instead of being in ground range projection, this product is aligned parallel to true north and corrected using either an Equidistant Rectangular, UTM or AMG map projection, as selected by the user. This type of image is the most appropriate for integration into existing GIS databases.
This is a multilook product. The multilook process reduces the noise and results in less speckle on the image. However, there is an increase in coarseness of the spatial resolution.
| Raw Data | Characteristics |
|---|---|
| Scene area (nominal) | 75km × 75km (approx.) |
| Spatial resolution | 16m range; 14m azimuth |
| Pixel size | 12.5m × 12.5m |
| Total product volume | 80-130Mbytes |
| Projections | UTM, AMG, Equidistant Rectangular |
| Effective No. of looks | 3 |
Details on acquision are available from JERS SAR Prices.