This product guide introduces all parts of the ASF sample InSAR products. It includes details of the InSAR processing flow, the data layers stored in the HDF5 data container, the browse imagery, and the metadata.
Legacy-Product Content Overview
The following files are in the sample InSAR, or interferometric, product suite:
HDF5 Product: ALPSR_06713_08055_0770.h5
Browse Image: ALPSR_06713_08055_0770.jpg
XML Metadata: ALPSR_06713_08055_0770.xml
KML Overlay: ALPSR_06713_08055_0770.amp.kmz
Log File: ALPSR_06713_08055_0770.log.txt
Product Specification Guide
The product-format specification defines the sample standard InSAR products generated at the Alaska Satellite Facility (ASF). It contains the definition for the HDF5 data container as well as the ISO-compliant XML metadata.
Viewing HDF5 Products
The sample InSAR HDF5 products are currently supported to different degrees by several software packages that can be used to investigate and visualize the data.
The commercial geographic information system ArcGIS recognizes the HDF5 structure and is able to extract the SAR data on the fly. The program does not calculate standard statistics for this data layer and is very slow in rendering the data this way. The map projection information must be manually defined.
The Geospatial Data Abstraction Library (GDAL) helps users explore the general contents of the sample InSAR HDF5 data. The gdalinfo tool summarizes the data structure in the file.
This Java-based tool, provided by the HDF group, enables browsing and editing of HDF files.
The Interactive Data Language (IDL) provides a more programmatic means to visualize the sample InSAR HDF5 data. In a first step, users can verify that the dataset is in HDF5 format.
InSAR Processing Flow
All ASF standardized sample InSAR products have been processed with a customized version of ROI_PAC (version 3.1, revision 172). The SAR interferometric products have been terrain-corrected using a digital elevation model (DEM) provided by Open Topography. In Spring 2014, tropospheric effects will be corrected using water vapor model outputs based on MODIS data provided by the Online Services for Correcting Atmosphere in Radar (OSCAR) of the Jet Propulsion Laboratory (JPL).
Figure 1. ASF Standardized InSAR Processing Flow.
Sample InSAR Products
The sample InSAR Products are distributed in HDF5.
The HDF5 product contains a data section with the actual imagery and a metadata section with detailed information that corresponds to each data set.
Figure 2. HDF5 Structure visualized with HDFView.
Within the sample InSAR HDF5 product there are five sets of data: correlation map, wrapped interferogram, unwrapped interferogram, DEM, and an incidence angle map.
Figure 3. Correlation Map.
The value range of the correlation map is between 0 (complete loss of correlation) to 1 (perfect correlation between master and slave image).
The wrapped interferogram contains phase information with fringes that limit the values within a range of -π and +π. The phase unwrapping produces continuous phase values that can be directly linked to terrain height with the baseline information. Referring to the product example presented in Figure 2, the phase value ranges from -14.839 to 9.201.
The DEM is used to remove topographic effects from the InSAR product.
The incidence angle map is derived from the DEM and is added for advanced analysis purposes.
The metadata section of the HDF5 product contains the metadata for the correlation map, wrapped and unwrapped interferogram, DEM, and incidence angle map, as well as metadata for the original SAR master and slave data used to generate the sample InSAR product.
The sample InSAR products are currently distributed with XML metadata. In Spring 2014, the sample InSAR products will be updated with ISO-compliant metadata.
Figure 4. Example of XML metadata file used to generate ISO-compliant metadata.
Browse Imagery and Overlay Files
ASF provides a browse image of the unwrapped interferogram in JPEG format and four KML overlay files in compressed KMZ format: amplitude, wrapped and unwrapped interferogram, and correlation.
Figure 5. Browse of unwrapped interferogram.
Figure 6. KML overlay of the terrain-corrected SAR amplitude image.