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Soil Column Sample Height Influences Soil Spectral Reflectance in Laboratory Experiment

Xu, Lu, Wang, Zhi-chun, Nyongesah, John Maina
Journal of the Indian Society of Remote Sensing 2019 v.47 no.7 pp. 1187-1196
analysis of variance, crystallization, irrigation, laboratory experimentation, models, particle size, reflectance, remote sensing, roughness, saline soils, sodium sulfate, soil salinity, soil salts, soil water, soil water content
Soil salt inversion models are basically calibrated in laboratory experiments and validated in the field. Unified standard about settings of soil column sample height (SCSH) is lacking. The main objective of this study was to identify the optimal SCSH for soil salinity estimation. Three types of soil particle size simulating soil roughness and ten different heights of soil column samples from 1 to 10 cm were designed, according to the previous studies, and soil spectral reflectance was measured before and after irrigation with deionized water. The spectrum, soil water content and soil salt amount (SA) on the surface of various soil column SHs in complex soil water system and soil roughness conditions were compared. Two-way ANOVA was applied to assess the effect of soil particle and salt crystallization on the spectral reflectance. Results indicated that SCSH caused distinct difference in salt accumulation at the surface (critical height is 6 cm) and in soil spectral reflectance (critical height is 2 cm) at the final state. Soil roughness influenced spectra significantly between the low-height samples (1–5 cm) and was covered up with SA at the surface between the high samples (6–10 cm). Considering the actual condition in the field, greater than 6 cm was deemed as an exact selection for saline soil in the region (Na₂SO₄). These results were critical to model soil salinity in laboratory experiment based on hyperspectral reflectance.