=== versions === python 3.12.0 | pystac-client 0.9.0 | planetary-computer 1.0.0 | rasterio 1.5.2 | osmnx 2.1.1 | numpy 2.5.4 | pandas 3.0.6 === reservoir outlines (OpenStreetMap) === reservoir id area_ha core_ha Howden 955357 62.4 33.6 Derwent 955161 69.5 42.9 Ladybower 1959653 198.1 124.8 Torside 8598540 62.6 42.0 === analysis grid === 817 x 738 pixels of 20 m (16.3 x 14.8 km), EPSG:32630 Howden 838 core water pixels Derwent 1073 core water pixels Ladybower 3129 core water pixels Torside 1046 core water pixels === STAC search === 821 Sentinel-2 L2A scenes of tile 30UWE with < 95% cloud, 02 Jan 2019 to 14 Oct 2026 {'02.12': 257, '03.00': 75, '04.00': 51, '05.09': 16, '05.10': 149, '05.11': 171, '05.12': 93, '05.13': 9} === reading Sentinel-2 over the reservoirs === 821 scenes already cached, 0 to read === quality control === reservoir Howden Derwent Ladybower Torside qc cloud or shadow 663 684 676 666 haze or glint 3 2 2 5 low sun 35 26 30 25 negative reflectance 10 10 5 9 ok 80 80 86 80 signal too dark 13 9 7 11 too few water pixels 17 10 15 25 326 usable reservoir-dates on 122 dates, 24 Feb 2019 to 22 Sep 2026 === why MNDWI fails on peaty water === rho_B03 rho_B11 mndwi scl_water_frac mndwi_pos_frac reservoir Howden 0.0100 0.0121 -0.0942 0.9335 0.0925 Derwent 0.0100 0.0129 -0.0920 0.8250 0.0920 Ladybower 0.0110 0.0121 -0.1394 0.8570 0.0890 Torside 0.0101 0.0142 -0.1662 0.8540 0.0055 === dates most worth investigating (NDCI robust z > 2) === date reservoir ndci ndci_z ndti green_blue sun_zenith flag 2023-05-21 Derwent 0.118 4.873 -0.088 0.947 34.8 check atmosphere (≥3 reservoirs high) 2025-04-10 Howden 0.115 3.922 -0.011 1.093 46.8 investigate 2019-09-17 Ladybower 0.205 3.484 0.000 0.660 51.9 investigate 2025-05-13 Derwent 0.093 3.331 0.025 1.167 35.9 investigate 2025-04-30 Derwent 0.131 3.261 -0.049 0.970 39.9 investigate 2020-08-12 Derwent 0.116 3.181 -0.121 0.866 40.0 investigate 2026-04-08 Howden 0.099 3.038 0.045 1.455 47.2 check atmosphere (≥3 reservoirs high) 2026-04-08 Torside 0.139 2.997 0.087 1.738 47.2 check atmosphere (≥3 reservoirs high) 2026-04-08 Ladybower 0.122 2.960 0.000 1.418 47.2 check atmosphere (≥3 reservoirs high) 2023-05-21 Howden 0.109 2.604 -0.106 0.932 34.8 check atmosphere (≥3 reservoirs high) 2026-03-04 Howden 0.098 2.602 0.150 0.515 61.1 investigate 2025-07-12 Howden 0.143 2.576 0.069 1.373 33.0 investigate === tidy CSV exports === howden_sentinel2_water_quality.csv 821 rows, 80 usable derwent_sentinel2_water_quality.csv 821 rows, 80 usable ladybower_sentinel2_water_quality.csv 821 rows, 86 usable torside_sentinel2_water_quality.csv 821 rows, 80 usable === median NDCI by season (n in brackets) === spring summer autumn Howden 0.035 (42) 0.045 (29) 0.071 (7) Derwent 0.044 (44) 0.038 (30) 0.038 (4) Ladybower 0.054 (48) 0.036 (32) 0.114 (3) Torside 0.042 (43) 0.007 (30) 0.042 (6) === whole-record medians === ndci mci ndti red green_blue n reservoir Howden 0.0412 0.0004 -0.0308 0.0094 0.8301 80 Derwent 0.0421 0.0002 -0.0395 0.0098 0.8525 80 Ladybower 0.0490 0.0003 -0.0355 0.0096 0.8828 86 Torside 0.0287 0.0007 -0.0078 0.0098 0.8245 80 === map date === 12 July 2026 S2B_MSIL2A_20260712T112109_R037_T30UWE_20260712T133747 sun zenith 33.0° Howden NDCI p10/median/p90 0.019 0.052 0.112 | NDTI median 0.028 Derwent NDCI p10/median/p90 0.023 0.059 0.110 | NDTI median 0.009 Ladybower NDCI p10/median/p90 0.023 0.056 0.100 | NDTI median 0.011 Torside NDCI p10/median/p90 0.017 0.041 0.070 | NDTI median 0.022 === Environment Agency samples (2019 onwards) === reservoir var n min max Derwent chlorophyll_ugl 47 2019-01-16 2026-08-13 Derwent colour_hazen 19 2019-01-16 2022-07-19 Howden chlorophyll_ugl 11 2019-01-16 2020-03-19 Howden colour_hazen 11 2019-01-16 2020-03-19 Ladybower chlorophyll_ugl 5 2026-04-20 2026-08-05 Ladybower colour_hazen 5 2026-04-20 2026-08-05 Torside chlorophyll_ugl 15 2019-02-11 2020-03-18 Torside colour_hazen 15 2019-02-11 2020-03-18 === satellite vs sample matches (within ±3 days) === reservoir sample_date s2_date value censored ndci mci Howden 2019-02-21 2019-02-24 0.50 True 0.0279 0.0023 Howden 2019-03-25 2019-03-28 0.60 False 0.0340 0.0012 Howden 2020-03-19 2020-03-22 0.50 True 0.0680 0.0006 Derwent 2019-02-21 2019-02-24 0.50 True 0.0333 0.0025 Derwent 2019-03-25 2019-03-28 0.50 True 0.0299 0.0011 Derwent 2021-06-18 2021-06-15 3.00 False 0.0451 -0.0004 Derwent 2022-04-20 2022-04-21 0.76 False 0.0352 0.0002 Derwent 2022-06-23 2022-06-20 8.70 False -0.0145 0.0013 Derwent 2022-08-10 2022-08-12 1.80 False 0.0548 0.0017 Derwent 2024-03-21 2024-03-24 0.59 False 0.0000 0.0004 Derwent 2025-05-15 2025-05-13 1.70 False 0.0925 0.0001 Derwent 2025-06-17 2025-06-17 1.30 False 0.0571 0.0004 Derwent 2026-04-21 2026-04-23 1.40 False 0.0704 -0.0005 Ladybower 2026-04-20 2026-04-23 1.80 False 0.0714 -0.0008 Ladybower 2026-07-10 2026-07-09 4.50 False 0.0159 0.0010 Ladybower 2026-08-05 2026-08-03 9.00 False -0.0435 0.0013 Torside 2019-04-24 2019-04-22 2.70 False 0.0649 -0.0000 Torside 2019-08-28 2019-08-25 5.00 False 0.0687 -0.0001 chlorophyll vs NDCI n = 18 Spearman rho = -0.03 p = 0.90 chlorophyll vs MCI n = 18 Spearman rho = -0.27 p = 0.28 colour vs B3/B2 n = 12 Spearman rho = -0.04 p = 0.91 === figures written === 01-locator-map.png 02-true-colour.png 03-ndci-map.png 04-turbidity-map.png 05-ndci-timeseries.png 06-monthly-climatology.png 07-in-situ-check.png