=== versions ===
python 3.12.0 | pystac-client 0.9.0 | planetary-computer 1.0.0 | rasterio 1.5.2 | numpy 2.5.4 | scipy 1.18.1 | geopandas 1.2.0

=== STAC search ===
13 scene slices from relative orbit 110; dates covering the whole box: 2026-09-05, 2026-09-11, 2026-09-17, 2026-09-23, 2026-09-29, 2026-10-11
2026-10-11: S1C_IW_GRDH_1SDV_20261011T055745_20261011T055810_009833_01397D_rtc, S1C_IW_GRDH_1SDV_20261011T055720_20261011T055745_009833_01397D_rtc
platform sentinel-1c | descending | polarisations ['VV', 'VH'] | ENL 4.4 | EPSG:32631

=== land mask ===
grid 4860 x 5066 pixels at 10 m (48.6 x 50.7 km)
WorldCover land 11.0%; open sea after a 250 m coastal buffer: 2,133 km² (86.6%)

=== CA-CFAR ===
Pfa 1e-06, ENL 4.4: threshold = 5.04 x local clutter mean (7.0 dB above it)
background ring 410 m to 1010 m wide; expected false-alarm pixels over pure gamma speckle: 21
detected pixels: VV 9,984, VH 25,941
VV: sea clutter median -9.6 dB; isolated speckle hits (clusters < 4 px) 623 = 2.9e-05 of sea pixels
VH: sea clutter median -25.1 dB; isolated speckle hits (clusters < 4 px) 892 = 4.2e-05 of sea pixels

=== targets ===
1,251 connected blobs in VV or VH -> 208 targets after merging blobs within 250 m and dropping those under 4 pixels
seen in both 144, VV only 19, VH only 45
median target-to-clutter ratio of targets seen in both: VV 16.6 dB, VH 23.2 dB

=== sidelobes and ambiguities ===
brightest target: VH 54.1 dB above clutter at row 602, col 4200
its sidelobe cross gives azimuth 9.2° and range 99.2° (grid bearings)
azimuth ambiguity offset lambda*R*PRF/(2V) for IW: 4.0-6.5 km
targets on the sidelobe cross of one >= 10 dB brighter: 35
targets at the ambiguity offset of one >= 10 dB brighter: 6

=== persistence across dates ===
5 other passes; main-date targets also found within 100 m on n other passes: {0: 94, 1: 18, 2: 7, 3: 7, 4: 6, 5: 76}
class
vessel                87
fixed structure       80
sidelobe              35
possible ambiguity     6

=== OpenStreetMap check ===
64 OSM wind turbines over open sea in the box; 100% have a target within 100 m (median offset 39 m)
fixed structures within 100 m of an OSM turbine: 63 of 80

=== result 2026-10-11 ===
87 vessels written to output/ship_detections_2026-10-11.geojson (all 208 targets kept, with a class column)
vessel extent median 152 m, largest 544 m; seen in VV 82%, in VH 79%, in both 61%
 class  pixels  blobs  extent_m  tcr_vv_db  tcr_vh_db  in_vv  in_vh  dates_seen     lon      lat
vessel   376.0      1     544.5       48.7       54.1   True   True           3 4.16453 52.24682
vessel   482.0      9     495.2       43.0       29.3   True   True           1 3.99061 51.97583
vessel   280.0      3     374.8       41.8       22.5   True   True           0 4.22320 52.20756
vessel   417.0      6     389.0       38.7       33.0   True   True           1 3.57532 51.90549
vessel   227.0      9     330.2       35.9       31.8   True   True           0 4.25611 52.19563

=== vessel counts per pass ===
      date    platform  targets  fixed  artefacts  vessels
2026-09-05 sentinel-1c      239     79         48      112
2026-09-11 sentinel-1d      250     75         30      145
2026-09-17 sentinel-1c      258     79         48      131
2026-09-23 sentinel-1d      305     79         54      172
2026-09-29 sentinel-1c      349     78        103      168
2026-10-11 sentinel-1c      208     80         41       87
mean 136 vessels per pass, range 87-172

=== figures ===
saved output/01-scene-vv-vh-land-mask.png
saved output/02-cfar-window-and-threshold.png
saved output/03-vv-vs-vh-anchorage.png
saved output/04-detections-map.png
saved output/05-sidelobes-and-turbines.png
saved output/06-counts-and-sizes.png