In the physiological monitoring of saline-alkali land reclamation vegetation, understanding the impacts of salt stress on plant spectral characteristics serves as the theoretical foundation for multispectral remote sensing. When plants are exposed to saline-alkali environments, high soil osmotic pressure restricts root water uptake, inducing physiological drought, stomatal closure, and reduced transpiration rates. Concurrently, the excessive accumulation of Na⁺ and Cl⁻ ions induces ion toxicity, disrupting chloroplast ultrastructure and suppressing chlorophyll biosynthesis. These physiological and biochemical alterations manifest distinctively in the canopy reflectance spectra: increased reflectance in the visible spectrum—particularly around the red absorption valley near 660 nm due to chlorophyll degradation; decreased reflectance in the near-infrared (NIR, 800–900 nm) band owing to cellular structure degradation and reduced leaf area index (LAI); and pronounced deepening or structural shifts in the short-wave infrared (SWIR, 1400–1900 nm) water absorption bands caused by decreased leaf fuel moisture status. By capturing reflectance data across these diagnostic bands, multispectral imagers extract specific vegetation indices highly correlated with stress severity, such as the Normalized Difference Vegetation Index (NDVI), Salinity Stress Index (SSI), Water Index (WI), and Normalized Difference Red Edge Index (NDRE), achieving rapid diagnostic modeling of plant salt-induced injury. Research indicates that the red edge position (REP) is exceptionally sensitive to salt stress. Under optimal physiological conditions, the plant red edge is typically situated between 700 nm and 730 nm. Salt stress triggers chlorophyll degradation and photosynthetic capacity suppression, driving the red edge position toward shorter wavelengths (a phenomenon termed "blue shift"), with the magnitude of this shift being positively correlated with stress intensity. Extracting reflectance values across the red edge spectral region (e.g., 670 nm, 700 nm, 730 nm, and 780 nm) via multispectral imagers allows the mathematical calculation of the red edge position and its dynamic trajectory, serving as a robust metric for evaluating salt tolerance among different species or reclamation treatments. The HG-MultiSP-800 UAV-borne lightweight multispectral camera, developed by Hagorun Technology Limited, integrates multiple dedicated spectral bands optimized for agricultural and ecological monitoring. It adapts seamlessly to both unmanned aerial vehicles and ground-based panning platforms, delivering a highly flexible and efficient data acquisition tool for vegetation physiological monitoring in saline-alkali regions. Distinct plant species and varying genotypes exhibit heterogeneous spectral response signatures under salt stress. Salt-tolerant varieties maintain higher relative chlorophyll concentrations and stable hydration profiles under salinity exposure; consequently, the rate of decline in their spectral indices relative to increasing soil electrical conductivity is significantly lower than that of salt-sensitive variants—a critical differentiator leveraged for early-stage germplasm screening.

Within saline-alkali land reclamation workflows, the screening of salt-tolerant plant germplasm resources represents a bottleneck for successful ecological restoration. Traditional evaluation protocols rely on measuring biomass accumulation, survival rates, and foliar ion concentrations under controlled salinity gradients—processes characterized by prolonged turnaround times, destructive sampling, and restricted analytical throughput. Multispectral imaging technology overcomes these limitations under both open-field and greenhouse pot-controlled conditions, executing high-throughput tracking of canopy spectral indices across diverse genotypes following salinity treatment. By monitoring change profiles in parameters such as NDVI, NDRE, and REP, researchers rapidly isolate salt-tolerant breeding lines that maintain stable spectral index outputs under stress. This non-destructive screening can be performed during early seedling or vegetative growth stages, drastically compressing breeding cycles while preserving valuable material for downstream propagation or genomic validation. Regarding dynamic plant physiological monitoring under salt stress, utilizing multispectral imagers to log canopy indices across chronological intervals (e.g., 1, 3, 7, and 14 days post-treatment) map the onset, propagation, and autogenous regulation pathways of salinity damage. The rate of decline in NDVI reflects the velocity of chlorophyll degradation and displays a strong negative correlation with foliar Na⁺ accumulation rates, while time-series changes in the water index (WI) track the plants' capacity for cellular turgor recovery. Integrating these hypercubes with destructive biochemical assays (such as leaf electrical conductivity, malondialdehyde content, and proline accumulation metrics) enables the construction of robust empirical models to upscale regional remote-sensing monitoring of vegetation salt injury. The HG-MultiSP-800 multispectral camera by Hagorun Technology Limited supports automated interval logging and remote control via mobile terminals, making it ideally configured for deployment at permanent monitoring stations within saline-alkali reclamation fields to capture multi-temporal physiological spectral datasets. For evaluating heterogeneous soil reclamation treatments (such as chemical amendment application, freshwater leaching, and halophyte cultivation), researchers can partition experimental blocks into discrete treatment plots. Periodically acquired multispectral imagery allows the calculation of mean NDVI and NDRE metrics across individual plots, enabling rigorous statistical comparisons of vegetation canopy cover and growth vigor to objectively judge short- and long-term reclamation efficacy and optimize soil management configurations.

Mounting multispectral imagers onto UAV platforms supports large-scale, high-frequency remote sensing diagnostics across saline-alkali reclamation zones. Although conventional point-based ground surveys yield high-accuracy soil salinity and plant physiological data, they suffer from restricted spatial representation and cannot capture field-scale spatial heterogeneity. UAV multispectral flights overcome this by delivering vegetation index distribution maps with centimeter-level spatial resolution, precisely mapping salinity hot-spots and localized zones of vegetation decline within treated fields to guide variable-rate precision agriculture operations (such as target amendment micro-dosing or localized irrigation adjustments). Comparing multi-temporal multispectral imagery across pre-implementation, active, and post-implementation phases provides objective, quantitative evidence of improvements in fractional vegetation cover (FVC), chlorophyll density, and canopy photosynthetic capacity, validating overall engineering efficacy. In the indirect inversion of spatial soil salinity distribution, researchers establish "soil salinity-vegetation spectral response" predictive models by leveraging the statistical correlations between foliar indices and soil electrical conductivity. Because the spectral features of salt-stressed vegetation and exposed salt crusts vary predictably with shifting salinity levels, applying multispectral image classification and spectral unmixing algorithms resolves the spatial boundaries and severity gradations of salinized patches, outputting high-fidelity digital soil salinity maps to guide precision land management. The HG-MultiSP-800 UAV-borne lightweight multispectral camera from Hagorun Technology Limited features a low-mass, low-power architecture that integrates seamlessly with a wide range of drone platforms. A single flight covers extensive saline-alkali experimental fields, and when combined with ground control points (GCPs), automatically generates high-accuracy orthomosaics and vegetation index maps, delivering a powerful, airborne monitoring solution for saline-alkali ecological restoration initiatives.

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