=== versions ===
python 3.12.0 | numpy 2.5.4 | scipy 1.18.1 | rasterio 1.5.2 | pystac-client 0.9.1

=== Step 1: search and read Sentinel-1 RTC ===
29 scenes from relative orbit 154, 06 Oct 2025 to 29 Mar 2026
target: S1A_IW_GRDH_1SDV_20260110T062247_20260110T062312_062701_07DC9E_rtc | sentinel-1a | looks 5 x 1 | nominal ENL 4.4 | EPSG:32630
read 29 chips of 1156 x 1316 pixels (10 m) in 20 s; NaN pixels in target: 0
target gamma0 VV: min 0.0018, median 0.0980, max 111.50 (linear)

=== Step 2: the multiplicative speckle model ===
window 1 (water): rows 671-691, cols 497-517 | reference CV 0.067 | mean -14.0 dB | ENL 6.65
window 2 (water): rows 597-617, cols 487-507 | reference CV 0.067 | mean -16.0 dB | ENL 5.48
window 3 (water): rows 593-613, cols 820-840 | reference CV 0.070 | mean -14.2 dB | ENL 5.87
window 4 (water): rows 679-699, cols 869-889 | reference CV 0.071 | mean -13.4 dB | ENL 6.65
window 5 (land ): rows 639-659, cols 1274-1294 | reference CV 0.078 | mean -8.1 dB | ENL 5.97
window 6 (land ): rows 39-59, cols 110-130 | reference CV 0.078 | mean -11.5 dB | ENL 8.56
window 7 (land ): rows 221-241, cols 681-701 | reference CV 0.079 | mean -7.5 dB | ENL 8.78
window 8 (land ): rows 1002-1022, cols 352-372 | reference CV 0.080 | mean -8.2 dB | ENL 5.68
ENL of the raw target image: 6.71 (nominal 4.4); speckle CV 0.386; reference ENL 187
normalised intensity in windows: mean 1.000, variance 0.153; gamma fit shape L = 6.80, scale 0.147
Kolmogorov-Smirnov distance: gamma(L=6.80) 0.020; single-look exponential 0.335
mean of dB pixels -11.95 dB vs dB of mean power -11.63 dB: bias -0.33 dB (theory for L=6.80: -0.33 dB)

=== Step 3: speckle filters ===
filtering with a 7 x 7 window and ENL = 6.7
Boxcar 7×7         15 ms  ( 98.9 Mpixel/s)
Lee                37 ms  ( 41.5 Mpixel/s)
Refined Lee       464 ms  (  3.3 Mpixel/s)
Enhanced Lee       58 ms  ( 26.0 Mpixel/s)
Frost             679 ms  (  2.2 Mpixel/s)
Gamma-MAP          52 ms  ( 29.3 Mpixel/s)

=== Step 4: ENL, edge preservation and the ratio image ===
edge pixels (top 10% Sobel gradient of the reference): 152,130
               ENL  ENL water  ENL land    EPI  ratio mean  ratio std  RMSE vs ref (dB)     ms
filter                                                                                        
None (raw)     6.7        6.2       7.2  0.781       1.000      0.000              2.14    0.0
Boxcar 7×7    56.4       40.7      72.1  0.401       0.977      0.402              1.58   15.0
Lee           52.1       35.7      68.4  0.811       0.970      0.299              1.49   37.0
Refined Lee   24.7       19.3      30.1  0.790       1.022      0.287              1.71  464.0
Enhanced Lee  55.4       39.3      71.4  0.806       0.978      0.324              1.49   58.0
Frost         48.0       34.5      61.6  0.808       0.974      0.315              1.48  679.0
Gamma-MAP     50.6       34.7      66.4  0.809       1.011      0.294              1.63   52.0
(pure speckle would give a ratio image with mean 1 and std 0.386)
raw image         : mean over homogeneous windows -11.63 dB; whole-chip mean power  -8.86 dB
boxcar in linear  : mean over homogeneous windows -11.63 dB; whole-chip mean power  -8.86 dB
boxcar in dB      : mean over homogeneous windows -11.91 dB; whole-chip mean power  -9.58 dB

=== Figures ===
figures written: 01-study-area-raw-and-reference.png, 02-speckle-statistics.png, 03-filter-comparison.png, 04-edge-transect.png, 05-enl-vs-epi.png, 06-ratio-images.png