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Table 1 Environmental covariates initially considered for soil quality prediction

From: Soil quality estimation using environmental covariates and predictive models: an example from tropical soils of Nigeria

Environmental covariates

Variable

Description

 DEM

AHShad

Analytical hillshade

 

Aspect

Aspect

 

CNBL

Cannel network base level

 

CIndex

Convergence index

 

Elv (m)

Elevation

 

LS (m)

Slope length factor

 

Plcurv

Plane curvature

 

Prcurv

Profile curvature

 

Slope (degree)

Land surface slope

 

TCA

Total catchment area

 

TWI

Topographic wetness index

 

VDepth

Valley depth: The relative height difference to the immediate adjacent channel lines

 Sentinel-2

B2

0.46 − 0.52 μm

 

B3

0.54–0.58 μm

 

B4

0.65–0.68 μm

 

B5

0.70–0.71 μm

 

B6

0.73 − 0.7 μm

 

B7

0.77 − 0.79 μm

 

B8

0.78 − 0.90 μm

 

B8A

0.85 − 0.87 μm

 

B11

1.56 − 1.65 μm

 

B12

2.10 − 2.28 μm

 

Carbonate index (CBI)

\({\text{CBI = }}\frac{{{\text{RED}}}}{{{\text{GREEN}}}}\)

 

Iron index (Fe)

\({\text{Fe = }}\frac{{{\text{RED}}}}{{{\text{BLUE}}}}\)

 

Clay index (CI)

\({\text{CI = }}\frac{{{\text{SWIR1}}}}{{{\text{SWIR2}}}}\)

 

Normalized Difference Build-up Index (NDBI)

\({\text{NDBI = }}\frac{{\text{(SWIR - NIR)}}}{{\text{(SWIR + NIR)}}}\)

 

Ratio Vegetation Index (RVI)

\({\text{RVI = }}\frac{{{\text{NIR}}}}{{{\text{RED}}}}\)

 

Modified Soil Adjusted Vegetation Index (MSAVI)

\({\text{MSAVI = }}\frac{{{{2 \times \text{NIR} + 1 - }}\sqrt {{{(2 \times \text{NIR}}}} {{ + 1)}}^{{{2}}} {{ - 8 \times (\text{NIR - RED})}}}}{{{2}}}\)

 

Normalized Difference Vegetation Index (NDVI)

\({\text{NDVI = }}\frac{{\text{(NIR - RED)}}}{{\text{(NIR + RED)}}}\)

 

Green Normalized Difference Vegetation Index (GNDVI)

\({\text{GNDVI = }}\frac{{\text{(NIR - GREEN)}}}{{\text{(NIR + GREEN)}}}\)

 

Land Surface Water Index (LSWI)

\({\text{LSWI = }}\frac{{\text{(NIR - SWIR)}}}{{\text{(NIR + SWIR)}}}\)

  1. Sentinel-2 (B2: blue, B3: green, B4: red, B5: red edge, B8: NIR, B8A: NIR, SWIR1: 11, SWIR2: 12); DEM digital elevation model