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Quality Control

Daisho.jl provides a suite of quality control functions for radar data. The QC workflow typically proceeds in several stages.

QC Workflow

1. Initialize QC Fields

Copy raw moments into QC arrays that will be progressively filtered:

qc_moments = Daisho.initialize_qc_fields(volume, raw_dict, qc_dict)

2. Apply Threshold Filters

Remove gates based on signal quality indicators:

# Remove gates with low SQI
qc_moments = Daisho.threshold_qc(volume.moments, raw_dict, qc_moments, qc_dict,
    "SQI", 0.3, "SQI", true)

# Remove gates with high spectrum width
qc_moments = Daisho.threshold_qc(volume.moments, raw_dict, qc_moments, qc_dict,
    "WIDTH", 8.0, "WIDTH", false)

Or apply multiple thresholds at once:

qc_moments = Daisho.threshold_qc(volume.moments, raw_dict, qc_moments, qc_dict,
    0.35, 6.0, 0.7, 8.0)  # SQI, SNR, RHOHV, WIDTH thresholds

3. Remove Speckle

Remove isolated gates (speckle) in range and azimuth:

qc_moments = Daisho.despeckle(3, qc_moments, qc_dict, n_gates, n_rays)
qc_moments = Daisho.despeckle_azimuthal(3, qc_moments, qc_dict, n_gates, n_rays)

4. PHIDP-Based Filtering

Remove gates with high differential phase variability:

qc_moments = Daisho.stddev_phidp_threshold(qc_moments, qc_dict, n_gates, n_rays, 11, 12)

5. Platform Motion Removal

For moving platforms (ships, aircraft), remove platform motion from radial velocity:

Daisho.remove_platform_motion!(volume, qc_moments, qc_dict)

6. Terrain Masking

Remove gates contaminated by ground clutter using SRTM elevation data:

qc_moments = Daisho.threshold_terrain_height(volume, raw_dict, qc_moments, qc_dict,
    5.0, "/path/to/srtm/tiles")

7. Sector Masking

Mask data in specific heading-relative azimuth sectors (e.g., ship superstructure blockage):

heading = get_heading_array(volume)
qc_moments = Daisho.mask_sector(volume, raw_dict, qc_moments, qc_dict,
    heading, 170.0, 190.0, "SQI")

SEA-POL Specific

For the SEA-POL C-band radar, RHOHV requires special handling:

Daisho.fix_SEAPOL_RHOHV!(volume, raw_dict)

Utility Functions