Question

Why spectral reflectance of dry soil is more than wet soil?

Answer 1

Spectral reflectance of Vegetation

• In the range from about 0.7 to 1.3 μm a plant leaf

typically reflects 40 - 50% of the energy incident

upon it primarily due to the internal structure of

plant leaves

• Because the internal structure of leaves are highly

variable between plant species, reflectance

measurements in this range often permit us to

discriminate between species (even if they look the

same in visible wavelengths)

• Many plant stresses alter the reflectance in this

region, and sensors operating in this range are often

used for vegetation stress detection

Spectral reflectance of Soil

• The factors that influence soil reflectance act over

less specified spectral bands

• Factors affecting soil reflectance are moisture

content, soil texture (proportion of sand, silt and

clay), surface roughness, presence of iron oxide and

organic matter content

• The presence of moisture in soil will decrease its

reflectance - this effect is greatest in the water

absorption bands at about 1.4, 1.9, 2.2 and 2.7 μm

• Soil moisture content is strongly related to the soil

texture

Spectral reflectance of Water

• Water (in soil, vegetation or water bodies)

absorbs radiation at near-IR wavelengths and

beyond (strong absorption bands at about 1.4,

1.9 and 2.7 μm)

• Reflectance from a water body can stem from

an interaction with:

– the water’s surface (specular reflection),

– with material suspended in the water, or

– with the bottom of the water body