nirs4all.operators.augmentation.environmental module

Environmental effects augmentation operators for spectral data.

This module provides wavelength-aware augmentation operators that simulate environmental effects on NIR spectra, including temperature-induced changes and moisture/water activity effects.

These operators inherit from SpectraTransformerMixin and automatically receive wavelength information from the dataset when used in nirs4all pipelines.

References

  • Maeda, H., Ozaki, Y., et al. (1995). Near infrared spectroscopy and chemometrics studies of temperature-dependent spectral variations of water. Journal of Near Infrared Spectroscopy, 3(4), 191-201.

  • Segtnan, V. H., et al. (2001). Studies on the structure of water using two-dimensional near-infrared correlation spectroscopy. Analytical Chemistry, 73(13), 3153-3161.

  • Luck, W. A. P. (1998). The importance of cooperativity for the properties of liquid water. Journal of Molecular Structure, 448(2-3), 131-142.

class nirs4all.operators.augmentation.environmental.MoistureAugmenter(water_activity_delta: float = 0.1, water_activity_range: tuple[float, float] | None = None, reference_water_activity: float = 0.5, free_water_fraction: float = 0.3, bound_water_shift: float = 25.0, moisture_content: float = 0.1, enable_shift: bool = True, enable_intensity: bool = True, random_state: int | None = None)[source]

Bases: SpectraTransformerMixin

Simulate moisture-induced spectral changes for data augmentation.

Water activity and moisture content affect NIR spectra through shifts in water bands between free and bound states. Higher water activity leads to more free water, while lower water activity means more water is hydrogen-bonded to the sample matrix.

Parameters:

  • water_activity_delta (float, default=0.1) – Change in water activity from reference (0-1 scale).

  • water_activity_range (tuple of (float, float), optional) – If provided, randomly sample water_activity_delta from this range for each sample.

  • reference_water_activity (float, default=0.5) – Reference water activity for the input spectra.

  • free_water_fraction (float, default=0.3) – Base fraction of water that is “free” vs. bound (0-1).

  • bound_water_shift (float, default=25.0) – Wavelength shift (nm) for bound water relative to free water.

  • moisture_content (float, default=0.10) – Base moisture content as fraction (affects intensity).

  • enable_shift (bool, default=True) – Apply water band position shifts.

  • enable_intensity (bool, default=True) – Apply water band intensity changes based on moisture content.

  • random_state (int, optional) – Random seed for reproducibility.

Variables:

_requires_wavelengths (bool) – Always True - this operator requires wavelength information.

Examples

>>> from nirs4all.operators.augmentation import MoistureAugmenter
>>> aug = MoistureAugmenter(water_activity_delta=0.2)
>>> X_aug = aug.transform(X, wavelengths=wavelengths)

>>> # Random moisture variation in pipeline
>>> aug = MoistureAugmenter(water_activity_range=(-0.2, 0.2))
>>> pipeline = [aug, PLSRegression(10)]

References

  • Büning-Pfaue, H. (2003). Analysis of water in food by near infrared spectroscopy. Food Chemistry, 82(1), 107-115.

  • Luck, W. A. P. (1998). The importance of cooperativity for the properties of liquid water. Journal of Molecular Structure.

BOUND_WATER_PEAK_1ST = 1460
BOUND_WATER_PEAK_COMB = 1940
FREE_WATER_PEAK_1ST = 1410
FREE_WATER_PEAK_COMB = 1920
class nirs4all.operators.augmentation.environmental.TemperatureAugmenter(temperature_delta: float = 5.0, temperature_range: tuple[float, float] | None = None, reference_temperature: float = 25.0, enable_shift: bool = True, enable_intensity: bool = True, enable_broadening: bool = True, region_specific: bool = True, random_state: int | None = None)[source]

Bases: SpectraTransformerMixin

Simulate temperature-induced spectral changes for data augmentation.

Temperature affects NIR spectra through: - Peak position shifts (especially O-H, N-H bands) - Intensity changes (hydrogen bonding disruption) - Band broadening (thermal motion)

This operator applies region-specific temperature effects based on literature values for NIR spectroscopy.

Parameters:

  • temperature_delta (float, default=5.0) – Temperature change from reference (°C). Positive = heating.

  • temperature_range (tuple of (float, float), optional) – If provided, randomly sample temperature_delta from this range for each sample. Overrides temperature_delta parameter.

  • reference_temperature (float, default=25.0) – Reference temperature for the input spectra (°C).

  • enable_shift (bool, default=True) – Apply peak position shifts.

  • enable_intensity (bool, default=True) – Apply intensity changes.

  • enable_broadening (bool, default=True) – Apply band broadening.

  • region_specific (bool, default=True) – Apply region-specific effects (recommended). If False, applies uniform average effects across all wavelengths.

  • random_state (int, optional) – Random seed for reproducibility.

Variables:

_requires_wavelengths (bool) – Always True - this operator requires wavelength information.

Examples

>>> from nirs4all.operators.augmentation import TemperatureAugmenter
>>> aug = TemperatureAugmenter(temperature_delta=10.0)
>>> X_aug = aug.transform(X, wavelengths=wavelengths)

>>> # Random temperature variation in pipeline
>>> aug = TemperatureAugmenter(temperature_range=(-5, 10))
>>> pipeline = [aug, PLSRegression(10)]

References

  • Maeda et al. (1995). JNIR Spectroscopy, 3(4), 191-201.

  • Segtnan et al. (2001). Analytical Chemistry, 73(13), 3153-3161.