ISCE2 (Interferometric Synthetic Aperture Radar Scientific Computing Environment)

ISCE uses XML documents for configuration. The structure relies on <component> and <property> tags.

Key Concepts:

• <component>: Represents a configurable part of the ISCE code. Names are case-insensitive. Components can contain nested components.
• <property>: Defines a single variable value within a component. Names are case-insensitive.
• <catalog>: Used to reference the contents of another XML file, allowing you to split large configurations into modular files.
• <constant>: Defines a constant value that can be used as a variable (e.g., $dir$) within the XML.

Example: Modular Configuration using <catalog>

Main file (stripmapApp.xml):

<stripmapApp>
    <component name="insar">
        <property name="Sensor name">ALOS</property>
        <component name="reference">
            <catalog>20070215.xml</catalog>
        </component>
        <component name="secondary">
            <catalog>20061231.xml</catalog>
        </component>
    </component>
</stripmapApp>

Referenced file (20070215.xml):

<component name="Reference">
    <property name="IMAGEFILE">/path/to/image</property>
    <property name="LEADERFILE">/path/to/leader</property>
    <property name="OUTPUT">20070215</property>
</component>

<!-- Example of a full stripmapApp configuration -->
<stripmapApp>
<component name="stripmapApp">
    <property name="sensor name">ALOS</property>
    <component name="Reference">
        <property name="IMAGEFILE">/a/b/c/20070215/IMG-HH-ALPSRP056480670-H1.0__A</property>
        <property name="LEADERFILE">/a/b/c/20070215/LED-ALPSRP056480670-H1.0__A</property>
        <property name="OUTPUT">20070215</property>
    </component>
    <component name="Secondary">
        <property name="IMAGEFILE">/a/b/c/20061231/IMG-HH-ALPSRP049770670-H1.0__A</property>
        <property name="LEADERFILE">/a/b/c/20061231/LED-ALPSRP049770670-H1.0__A</property>
        <property name="OUTPUT">20061231</property>
    </component>
</component>
</stripmapApp>

In ISCE2, the insarApp.py application uses an insarApp.xml input file to define processing parameters. To keep the main configuration file clean, you can use "catalogs"—external XML files that contain specific data for components like reference or secondary.

When a <catalog> tag is used within a component in insarApp.xml, the contents of that catalog file (excluding its top-level root tag) are parsed and directly inserted into the main configuration. This allows you to reuse sensor-specific data structures (e.g., reference_alos.xml) across different projects.

Usage Pattern

1. Define your main insarApp.xml with <catalog> tags pointing to your external files.
2. Create sensor-specific catalog files (e.g., reference_SENSOR.xml) containing the <component> definitions.
3. Alternatively, you can use an "All-in-One" style where all properties are defined directly inside insarApp.xml without external references.

<!-- insarApp.xml -->
<insarApp>
    <component name="insar">
        <property name="Sensor name">ALOS</property>
        <component name="reference">
            <catalog>reference_alos.xml</catalog>
        </component>
        <component name="secondary">
            <catalog>secondary_alos.xml</catalog>
        </component>
    </component>
</insarApp>

<!-- reference_alos.xml -->
<component name="Reference">
    <property name="IMAGEFILE">/<path-to-your-file>/IMG-HH-ALPSRP056480670-H1.0__A</property>
    <property name="LEADERFILE">/<path-to-your-file>/LED-ALPSRP056480670-H1.0__A</property>
    <property name="OUTPUT">20070215.raw</property>
</component>

PyCuAmpcor follows a multi-step procedure to estimate offsets:

1. Coarse Window Loading: Loads a reference window and a larger secondary chip (sized by the search range) to allow for shifts.
2. Initial Cross-Correlation: Computes a normalized correlation surface using either frequency or time domain algorithms. It finds the peak position and extracts statistics (SNR, variance) around it.
3. Secondary Window Extraction: Extracts a smaller window from the secondary image centered around the initial peak position to prepare for oversampling.
4. Window Oversampling: Both windows are oversampled (typically by a factor of 2) using FFT to prevent aliasing. For TOPSAR, the magnitude is used (derampMethod=0) to avoid issues with quadratic phase ramps.
5. Fine Cross-Correlation: Performs correlation on the oversampled windows to produce a high-resolution correlation surface.
6. Final Peak Detection: The correlation surface is further oversampled (using FFT or sinc), and the final offset is calculated using the formula: offset = (OffsetInit - halfSearchRange) + OffsetZoomIn / (oversamplingFactor * rawDataOversamplingFactor) Note: Users must manually add any pre-defined gross offsets to this result.

ISCE2 applications (like stripmapApp.py) are composed of multiple Component objects. Each component is configurable via XML files or command-line arguments.

Component Naming Model

Every configurable component has two identifiers used to locate configuration files:

1. Family Name: A broad identifier shared by all instances of a specific class (e.g., the family name for stripmapApp.py is insar).
2. Instance Name: A unique identifier for a specific instance of a component within an application (e.g., stripmapApp is an instance of the insar family).

Configuration Priority (Layered Approach)

ISCE2 uses a layered configuration system where higher-priority sources overwrite values from lower-priority sources. The priority sequence (from lowest to highest) is:

1. Environment Variable (ISCEDB): XML files placed in the directory defined by the ISCEDB environment variable. Use this for global settings.
2. Local Directory: XML files located in the directory where the application is executed.
3. Command Line:
   • Arguments passed as XML filenames (e.g., stripmapApp.py myInput.xml).
   • Direct parameter overrides using the syntax family.instance.parameter=value (e.g., insar.reference.output=reference_c.raw).

Within each location, files named after the family name are loaded first, and files named after the instance name are loaded second, overwriting the family-level settings.

# Example of command line override (Highest Priority)
stripmapApp.py insar.reference.output=reference_c.raw