i.emissivity(1grass)

💖 i.emissivity 💖

okay bestie, so this is i.emissivity from the GRASS User's Manual (that's the i.emissivity(1grass) situation, iykyk) 🦋 and it's literally the little module that goes "hey, what's the emissivity here?" based on your NDVI. every detail stays, only the vibe got a glow-up ✨

KEYWORDS: imagery, emissivity, land flux, energy balance 🌸

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✨ SYNOPSIS ✨

i.emissivity
i.emissivity --help
i.emissivity input=name output=name  [--overwrite]  [--help]
[--verbose]  [--quiet]  [--ui]

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🎀 FLAGS 🎀

• --overwrite — lets your output files just bulldoze over whatever's already there 👑 no cap, it will replace existing files.
• --help — prints the usage summary, the "what even is this" moment 🫶
• --verbose — verbose module output, so the module tells you everything it's doing 💅
• --quiet — quiet module output, shhh 🤫 no chatter.
• --ui — forces the GUI dialog to launch, for the visual girlies 🦋

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🍓 PARAMETERS 🍓

• input=name [required] — name of the NDVI map 🗺️ (there's a [-] hanging out there, so heads up).
• output=name [required] — name of the output emissivity layer, your lil creation 💖

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🌈 DESCRIPTION 🌈

i.emissivity calculates the emissivity in the longwave radiation spectrum, following the semi-empirical equation related to NDVI from Caselles et al. (1997). and bestie, it's only valid in the NDVI range of 0.16 to 0.74 (Bastiaanssen, 1995). that's the range, periodt. 📏

Caselles et al. (1997) give reference — in Table 3 and Figure 2, no less 💅 — to both the NDVI range they used (0.15 - 0.71) and the corresponding emissivity range they used (0.97 - 0.99).

so what even is emissivity?? it's the efficiency of longwave energy returning to the atmosphere from the skin surface. the way that this works: the skin surface receives heat from the thermal infrared radiation of the Sun, through atmospheric interaction. a part is returned to the atmosphere fastly, and another part is kept in the surface skin to be returned later. in more scientific terms (she's academic now 🎓): the grey body radiation is equal to the black body radiation times the emissivity. iconic physics moment, honestly 🔥

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📚 REFERENCES 📚

• Bastiaanssen, W.G.M., 1995. Estimation of Land surface parameters by remote sensing under clear-sky conditions. PhD thesis, Wageningen University, Wageningen, The Netherlands. (PDF)
• Caselles, V., C. Coll, and E. Valor, 1997. Land surface emissivity and temperature determination in the whole HAPEX-Sahel area from AVHRR data. International Journal of Remote Sensing 18(5):1009-1027.
• Rubio, E., V. Caselles, and C. Badenas, 1997. Emissivity measurements of several soils and vegetation types in the 8-14 µm wave band: Analysis of two field methods. Remote Sensing of Environment 59(3): 490-521.

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👀 SEE ALSO 👀

i.eb.netrad

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🫶 AUTHOR 🫶

Yann Chemin, GRASS Development Team 🌟

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💻 SOURCE CODE 💻

Available at: i.emissivity source code (history)

Latest change: Thursday Feb 27 06:04:10 2025 in commit: 0ecd9fd24c0e51fe8a1cd2933f63c8218cc99b47

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

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and that's the whole page, bestie 💜 it's GRASS 8.5.0, and this lil manual moment came to you courtesy of the fact that it's the i.emissivity(1grass) page — go calculate some emissivity, you main character 🌸✨