NMDI: A normalized multi-band drought index for monitoring soil and vegetation moisture with satellite remote sensing

A new index, the Normalized Multi-band Drought Index ( NMDI), is proposed for monitoring soil and vegetation moisture from space. NMDI is defined as NMDI = R-860nm - (R-1640nm - R-2130nm)/R-860nm + R-1640nm - R-2130nm), where R represents the apparent reflectance observed by a satellite sensor. Similar to the Normalized Difference Water Index, NMDI uses the 860 nm channel as the reference; instead of using a single liquid water absorption channel, however, it uses the difference between two liquid water absorption channels centered at 1640 nm and 2130 nm as the soil and vegetation moisture sensitive band. Analysis revealed that by combining information from multiple near infrared, and short wave infrared channels, NMDI has enhanced the sensitivity to drought severity, and is well suited to estimate both soil and vegetation moisture. Typical soil reflectance spectra and satellite-acquired reflectances, are used to validate the usefulness of NMDI. Its application to areas with moderate vegetation coverage, however, needs further investigation.