i.landsat.acca(1grass)

💖 i.landsat.acca — bestie's guide to cloud-spotting from SPACE 🛰️✨

okay so. you know that one GRASS module literally called i.landsat.acca? yeah. she does Landsat TM/ETM+ Automatic Cloud Cover Assessment (ACCA). that's it, that's the name, she's not subtle and honestly? iconic. 👑

keywords, if you're searching: imagery, ACCA, cloud detection, satellite, Landsat

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✨ SYNOPSIS ✨

the way she shows up when you type her name:

i.landsat.acca
i.landsat.acca --help
i.landsat.acca [-5fx2s] input=basename output=name  [b56composite=float]
[b45ratio=float]   [histogram=integer]   [--overwrite]  [--help]
[--verbose]  [--quiet]  [--ui]

🎀 Flags

• -5 — this data is Landsat-5 TM. i.e. the thermal band is .6, not .61. lowkey important, don't skip it.
• -f — apply that post-processing filter to yeet the small holes 🕳️
• -x — always use the cloud signature (step 14). no second-guessing, we commit.
• -2 — bypass the second-pass processing and merge warm (not ambiguous) clouds with cold clouds. two passes? not today.
• -s — include a whole extra category for cloud shadows 🌥️
• --overwrite — let output files bulldoze existing files. she said out with the old.
• --help — print usage summary
• --verbose — verbose module output (she talks a lot, we love that)
• --quiet — quiet module output (she shuts up, also valid)
• --ui — force launching the GUI dialog 🖱️

🦋 Parameters

• input=basename — required. Base name of input raster bands. Example: B. for B.1, B.2, ...
• output=name — required. Name for the output raster map.
• b56composite=float — B56composite (step 6). Default: 225.
• b45ratio=float — B45ratio: Desert detection (step 10). Default: 1.
• histogram=integer — Number of classes in the cloud temperature histogram. Default: 100

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🌸 DESCRIPTION 🌸

i.landsat.acca implements the Automated Cloud-Cover Assessment (ACCA) Algorithm from Irish (2000), with the constant values for pass filter one from Irish et al. (2006).

to do all of this she needs Landsat band numbers 2, 3, 4, 5, and 6 (or band 61 for Landsat-7 ETM+), which — and this is the part people forget 😭 — have already been processed from DN into reflectance and band-6 temperature with i.landsat.toar).

fr fr, do that step first. she's not doing it for you.

so the ACCA algorithm gives good results over most of the planet 🌍 with the exception of ice sheets, because ACCA operates on the premise that clouds are colder than the land surface they cover (and ice sheets are like... already cold, bestie, the vibe check fails 💀). The algorithm was designed for Landsat-7 ETM+, but because reflectance is used, it's also useful for Landsat-4/5 TM. ate. 🔥

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📝 NOTES 📝

i.landsat.acca works in the current region settings. yes, current. set your region before you run her, she's not going to guess.

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🌈 EXAMPLES 🌈

okay so here's the standard ACCA algorithm run, with filling of small cloud holes (that's the -f flag):

with per-band reflectance raster maps named 226_62.toar.1, 226_62.toar.2, ... and the LANDSAT-7 thermal band 226_62.toar.61, outputting to a new raster map named 226_62.acca:

i.landsat.toar sensor=7 gain=HHHLHLHHL date=2003-04-07 \
  product_date=2008-11-27 band_prefix=226_62 solar_elevation=49.51654
i.landsat.acca -f band_prefix=226_62.toar output=226_62.acca

see how we did i.landsat.toar first? 👀 told you.

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📚 REFERENCES 📚

• Irish R.R., Barker J.L., Goward S.N., and Arvidson T., 2006. Characterization of the Landsat-7 ETM+ Automated Cloud-Cover Assessment (ACCA) Algorithm. Photogrammetric Engineering and Remote Sensing vol. 72(10): 1179-1188.
• Irish, R.R., 2000. Landsat 7 Automatic Cloud Cover Assessment. In S.S. Shen and M.R. Descour (Eds.): Algorithms for Multispectral, Hyperspectral, and Ultraspectral Imagery VI. Proceedings of SPIE, 4049: 348-355.

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👀 SEE ALSO 👀

i.atcorr, i.landsat.toar

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🫶 AUTHOR 🫶

E. Jorge Tizado (ej.tizado unileon es), Dept. Biodiversity and Environmental Management, University of León, Spain

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💾 SOURCE CODE 💾

Available at: i.landsat.acca source code (history)

Latest change: Thursday May 08 14:35:40 2025 in commit: 9528b1e38ba37992c1597a979dc3efbb07b74ec5

Main index | Imagery index | Topics index | Keywords index | Graphical index | Full index

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© 2003-2026 GRASS Development Team, GRASS 8.5.0 Reference Manual

and that's the whole page bestie 💅 go detect some clouds, it's giving main character energy, no cap. GRASS 8.5.0 out. 🎀✨🦋