BSI: Isolating Bare Soil From Everything Growing On It
Bare ground has a spectral fingerprint all its own — high in red and SWIR, low in NIR and blue — and BSI combines all four bands to separate exposed soil from vegetation and water in a single number.
How it reads the surface
The numerator plays soil's bright bands (SWIR1 + Red) against vegetation's (NIR + Blue), so exposed ground rises while canopy and water fall. Drawing on four bands makes BSI more robust than a two-band ratio at the tricky soil/vegetation edge.
The math behind it
where SWIR1 is shortwave-infrared 1 reflectance (~1.6 µm), Red is red reflectance, NIR is near-infrared reflectance, Blue is blue reflectance.
How to interpret the output
Higher = more exposed bare soil; low or negative = vegetated or water-covered ground.
The bands it needs
| Sentinel-2 | SWIR1 B11 · Red B4 · NIR B8 · Blue B2 |
| Landsat 8/9 | SWIR1 B6 · Red B4 · NIR B5 · Blue B2 |
Real-world use
BSI supports desertification and land-degradation monitoring, fallow-field detection in agriculture, and erosion and mining-footprint mapping.
Watch out for
Soil moisture and soil type shift BSI values, and some dry built-up materials mimic bare soil — for change work, compare BSI on similar-season, similar-moisture dates rather than across wet and dry periods.
Compute BSI on your own study area
Skip the code. Draw or upload a boundary and Spatial Research Suite runs BSI on live Sentinel-2 or Landsat imagery — with cloud masking, exports and citations built in.
Run this analysis in GISforus →Frequently asked
What does a high BSI value mean?
Strongly exposed bare soil; vegetated and water-covered ground return low or negative values.
Does soil moisture affect BSI?
Yes — wet soil reads differently from dry, so compare dates with similar moisture and season for reliable change analysis.