H/A/α Decomposition (halphafp)#

polsartools.halphafp(infolder, window_size=1, outType='tif', cog_flag=False, cog_overviews=[2, 4, 8, 16], write_flag=True, max_workers=None, block_size=(512, 512), progress_callback=None)[source]

Perform H/α/A (Entropy/Alpha/Anisotropy) decomposition for full-pol SAR data.

This function implements the Cloude-Pottier decomposition, computing entropy (H), alpha angle (α), anisotropy (A), and normalized eigenvalues from full-polarimetric SAR coherency (T3) or covariance (C3) matrices. This decomposition is fundamental for understanding scattering mechanisms in polarimetric SAR data.

Examples

>>> # Basic usage with default parameters
>>> halphafp("/path/to/fullpol_data")

>>> # Advanced usage with custom parameters
>>> halphafp(
...     infolder="/path/to/fullpol_data",
...     window_size=5,
...     outType="tif",
...     cog_flag=True,
...     block_size=(1024, 1024)
... )
Parameters:

  • infolder (str) – Path to the input folder containing full-pol T3 or C3 matrix files.

  • window_size (int, default=1) – Size of the spatial averaging window. Larger windows improve eigenvalue/eigenvector estimation but decrease spatial resolution.

  • outType ({'tif', 'bin'}, default='tif') – Output file format: - ‘tif’: GeoTIFF format with georeferencing information - ‘bin’: Raw binary format

  • cog_flag (bool, default=False) – If True, creates Cloud Optimized GeoTIFF (COG) outputs with internal tiling and overviews for efficient web access.

  • cog_overviews (list[int], default=[2, 4, 8, 16]) – Overview levels for COG creation. Each number represents the decimation factor for that overview level.

  • write_flag (bool, default=True) – If True, writes results to disk. If False, only processes data in memory.

  • max_workers (int | None, default=None) – Maximum number of parallel processing workers. If None, uses CPU count - 1 workers.

  • block_size (tuple[int, int], default=(512, 512)) – Size of processing blocks (rows, cols) for parallel computation. Larger blocks use more memory but may be more efficient.

Returns:

Writes six output files to disk: 1. H_fp: Entropy (H) [0-1] 2. alpha_fp: Alpha angle (α) [0°-90°] 3. anisotropy_fp: Anisotropy (A) [0-1] 4. e1_norm: Normalized first eigenvalue 5. e2_norm: Normalized second eigenvalue 6. e3_norm: Normalized third eigenvalue

Return type:

None

Notes

The H/α/A decomposition provides three main parameters:

  1. Entropy (H): - Range: [0, 1] - H = 0: Single scattering mechanism - H = 1: Random mixture of scattering mechanisms - Formula: H = -∑(pᵢ log₃(pᵢ)), where pᵢ are normalized eigenvalues

  2. Alpha angle (α): - Range: [0°, 90°] - α ≈ 0°: Surface scattering - α ≈ 45°: Volume scattering - α ≈ 90°: Double-bounce scattering - Formula: α = ∑(pᵢαᵢ), where αᵢ are individual alpha angles

  3. Anisotropy (A): - Range: [0, 1] - Measures relative importance of secondary mechanisms - A = (λ₂ - λ₃)/(λ₂ + λ₃), where λᵢ are eigenvalues

Applications: - Land cover classification - Forest type mapping - Urban area analysis - Agricultural monitoring - Target detection - Change detection - Soil moisture estimation

References

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