Remote Sensing of SoilsRemote Sensing of SoilsRemote Sensing of SoilsRemote Sensing of Soils

•• 26% of the Earth’s surface is exposed land26% of the Earth’s surface is exposed land•• 74% of the Earth’s surface is covered by water74% of the Earth’s surface is covered by water•• Almost all humanity lives on the terrestrial, solid Earth Almost all humanity lives on the terrestrial, solid Earth comprised of bedrock and the weathered bedrock called comprised of bedrock and the weathered bedrock called soilsoil. . •• Remote sensing can play a limited role in the identification, inventory, and Remote sensing can play a limited role in the identification, inventory, and mapping of mapping of surficial soilssurficial soils not covered with dense vegetation. not covered with dense vegetation.•• Remote sensing can provide information about the Remote sensing can provide information about the chemical compositionchemical composition of of rocks and minerals that are on the Earth’s surface, and not completely covered rocks and minerals that are on the Earth’s surface, and not completely covered by dense vegetation. Emphasis is placed on understanding unique by dense vegetation. Emphasis is placed on understanding unique absorption absorption bandsbands associated with specific types of rocks and minerals using imaging associated with specific types of rocks and minerals using imaging spectroscopy techniques. spectroscopy techniques. •• Remote sensing can also be used to extract Remote sensing can also be used to extract geologic informationgeologic information including, including, lithology, structure, drainage patterns, and geomorphology (landforms).lithology, structure, drainage patterns, and geomorphology (landforms).

•• 26% of the Earth’s surface is exposed land26% of the Earth’s surface is exposed land•• 74% of the Earth’s surface is covered by water74% of the Earth’s surface is covered by water•• Almost all humanity lives on the terrestrial, solid Earth Almost all humanity lives on the terrestrial, solid Earth comprised of bedrock and the weathered bedrock called comprised of bedrock and the weathered bedrock called soilsoil. . •• Remote sensing can play a limited role in the identification, inventory, and Remote sensing can play a limited role in the identification, inventory, and mapping of mapping of surficial soilssurficial soils not covered with dense vegetation. not covered with dense vegetation.•• Remote sensing can provide information about the Remote sensing can provide information about the chemical compositionchemical composition of of rocks and minerals that are on the Earth’s surface, and not completely covered rocks and minerals that are on the Earth’s surface, and not completely covered by dense vegetation. Emphasis is placed on understanding unique by dense vegetation. Emphasis is placed on understanding unique absorption absorption bandsbands associated with specific types of rocks and minerals using imaging associated with specific types of rocks and minerals using imaging spectroscopy techniques. spectroscopy techniques. •• Remote sensing can also be used to extract Remote sensing can also be used to extract geologic informationgeologic information including, including, lithology, structure, drainage patterns, and geomorphology (landforms).lithology, structure, drainage patterns, and geomorphology (landforms).

Remote Sensing of Soils, Remote Sensing of Soils, Minerals, and GeomorphologyMinerals, and Geomorphology

Remote Sensing of Soils, Remote Sensing of Soils, Minerals, and GeomorphologyMinerals, and Geomorphology

•• SoilSoil is unconsolidated material at the surface of the Earth that is unconsolidated material at the surface of the Earth that serves as a natural medium for growing plants. Plant roots reside serves as a natural medium for growing plants. Plant roots reside within this material and extract water and nutrients. Soil is the within this material and extract water and nutrients. Soil is the weathered material between the atmosphere at the Earth’s surface weathered material between the atmosphere at the Earth’s surface and the bedrock below the surface to a maximum depth of and the bedrock below the surface to a maximum depth of approximately 200 cm (USDA, 1998).approximately 200 cm (USDA, 1998).

•• SoilSoil is a mixture of inorganic mineral particles and organic is a mixture of inorganic mineral particles and organic matter of varying size and composition. The particles make up matter of varying size and composition. The particles make up about 50 percent of the soil’s volume. Pores containing air about 50 percent of the soil’s volume. Pores containing air and/water occupy the remaining volume. and/water occupy the remaining volume.

•• SoilSoil is unconsolidated material at the surface of the Earth that is unconsolidated material at the surface of the Earth that serves as a natural medium for growing plants. Plant roots reside serves as a natural medium for growing plants. Plant roots reside within this material and extract water and nutrients. Soil is the within this material and extract water and nutrients. Soil is the weathered material between the atmosphere at the Earth’s surface weathered material between the atmosphere at the Earth’s surface and the bedrock below the surface to a maximum depth of and the bedrock below the surface to a maximum depth of approximately 200 cm (USDA, 1998).approximately 200 cm (USDA, 1998).

•• SoilSoil is a mixture of inorganic mineral particles and organic is a mixture of inorganic mineral particles and organic matter of varying size and composition. The particles make up matter of varying size and composition. The particles make up about 50 percent of the soil’s volume. Pores containing air about 50 percent of the soil’s volume. Pores containing air and/water occupy the remaining volume. and/water occupy the remaining volume.

Soil CharacteristicsSoil CharacteristicsSoil CharacteristicsSoil Characteristics

•• We no longer identify a “soil type”. Rather, soil scientists determine the We no longer identify a “soil type”. Rather, soil scientists determine the soil soil taxonomytaxonomy (Petersen, 1999). (Petersen, 1999). ““Keys to Soil TaxonomyKeys to Soil Taxonomy”” have been used by the have been used by the USDA Natural Resources Conservation Service since 1975 to qualitatively and USDA Natural Resources Conservation Service since 1975 to qualitatively and quantitatively differentiate between soil quantitatively differentiate between soil taxataxa. The highest category of the U.S. . The highest category of the U.S. Soil Taxonomy is Soil Taxonomy is Soil OrderSoil Order. Each order reflects the dominant soil-forming . Each order reflects the dominant soil-forming processes and the degree of soil formation. processes and the degree of soil formation.

•• There are 12 dominant U.S. There are 12 dominant U.S. Soils OrdersSoils Orders: Alfisols (high-nutrient soils), : Alfisols (high-nutrient soils), Andisols (volcanic soils), Aridisols (desert soils), Entisols (new soils), Gelisols Andisols (volcanic soils), Aridisols (desert soils), Entisols (new soils), Gelisols (tundra soils), Histosols (organic soils), Inceptisols (young soils), Mollisols (tundra soils), Histosols (organic soils), Inceptisols (young soils), Mollisols (prairie soils), Oxisols (tropical soils),Spodosols (forest soils), Ultisols (low-(prairie soils), Oxisols (tropical soils),Spodosols (forest soils), Ultisols (low-nutrient sols), and Verticols (swelling-clay soils). Scientists use Dichotomous nutrient sols), and Verticols (swelling-clay soils). Scientists use Dichotomous Keys to classify soils into Suborder, Great Groups, Subgroups, Family Level, Keys to classify soils into Suborder, Great Groups, Subgroups, Family Level, and Soil Series.and Soil Series.

•• We no longer identify a “soil type”. Rather, soil scientists determine the We no longer identify a “soil type”. Rather, soil scientists determine the soil soil taxonomytaxonomy (Petersen, 1999). (Petersen, 1999). ““Keys to Soil TaxonomyKeys to Soil Taxonomy”” have been used by the have been used by the USDA Natural Resources Conservation Service since 1975 to qualitatively and USDA Natural Resources Conservation Service since 1975 to qualitatively and quantitatively differentiate between soil quantitatively differentiate between soil taxataxa. The highest category of the U.S. . The highest category of the U.S. Soil Taxonomy is Soil Taxonomy is Soil OrderSoil Order. Each order reflects the dominant soil-forming . Each order reflects the dominant soil-forming processes and the degree of soil formation. processes and the degree of soil formation.

•• There are 12 dominant U.S. There are 12 dominant U.S. Soils OrdersSoils Orders: Alfisols (high-nutrient soils), : Alfisols (high-nutrient soils), Andisols (volcanic soils), Aridisols (desert soils), Entisols (new soils), Gelisols Andisols (volcanic soils), Aridisols (desert soils), Entisols (new soils), Gelisols (tundra soils), Histosols (organic soils), Inceptisols (young soils), Mollisols (tundra soils), Histosols (organic soils), Inceptisols (young soils), Mollisols (prairie soils), Oxisols (tropical soils),Spodosols (forest soils), Ultisols (low-(prairie soils), Oxisols (tropical soils),Spodosols (forest soils), Ultisols (low-nutrient sols), and Verticols (swelling-clay soils). Scientists use Dichotomous nutrient sols), and Verticols (swelling-clay soils). Scientists use Dichotomous Keys to classify soils into Suborder, Great Groups, Subgroups, Family Level, Keys to classify soils into Suborder, Great Groups, Subgroups, Family Level, and Soil Series.and Soil Series.

Soil TaxonomySoil TaxonomySoil TaxonomySoil Taxonomy

Standard Soil Standard Soil Profile Profile

(U.S. Department (U.S. Department of Agriculture)of Agriculture)

Standard Soil Standard Soil Profile Profile

(U.S. Department (U.S. Department of Agriculture)of Agriculture)

Soil Particle Size ScalesSoil Particle Size ScalesSoil Particle Size ScalesSoil Particle Size Scales

0.002 0.05 0.1 0.25 0.5 1 2 mm

Particle size relative to a grain of sand 0.15 mm in diameter

Sand

SiltClay

Clay SiltSand

v. fine fine medium coarse v. coarseGravel

0.002 0.06 0.2 2 mm

Clay Silt SandGravel Stones

fine medium coarse

0.006 0.02 0.6

0.15 mm

fine medium coarse

76.2

0.002 0.2 2 mm

Clay SiltSand

Gravel

0.02

fine coarse

a. Soil Science Society of America and U.S. Department of Agriculture Soil Particle Size Scale

b. MIT and British Standards Institute

c. International Society of Soil Science

0.002 0.05 0.1 0.25 0.5 1 2 mm

Particle size relative to a grain of sand 0.15 mm in diameter

Sand

SiltClay

Clay SiltSand

v. fine fine medium coarse v. coarseGravel

0.002 0.06 0.2 2 mm

Clay Silt SandGravel Stones

fine medium coarse

0.006 0.02 0.6

0.15 mm

fine medium coarse

76.2

0.002 0.2 2 mm

Clay SiltSand

Gravel

0.02

fine coarse

a. Soil Science Society of America and U.S. Department of Agriculture Soil Particle Size Scale

b. MIT and British Standards Institute

c. International Society of Soil Science

Soil Texture TriangleSoil Texture TriangleSoil Texture TriangleSoil Texture Triangle100

90

80

70

60

50

40

30

20

10

100

100 90 80 70 60 50 40 30 20 10

90

80

70

60

50

40

30

20

10

Cla

y (%

)

Sand (%)

Silt (%)

read

read

read

Clay

SiltSand

loamysand

sandy loam

Loam

sandy clay loam

silty clay

silty clay loam

clay loam

sandy clay

silt loam

100

90

80

70

60

50

40

30

20

10

100

100 90 80 70 60 50 40 30 20 10

90

80

70

60

50

40

30

20

10

Cla

y (%

)

Sand (%)

Silt (%)

read

read

read

Clay

SiltSand

loamysand

sandy loam

Loam

sandy clay loam

silty clay

silty clay loam

clay loam

sandy clay

silt loam

Cla

y (%

)

Sand (%)

Silt (%)

Total Upwelling Radiance (Total Upwelling Radiance (LLtt) Recorded by a Remote ) Recorded by a Remote

Sensing System over Exposed Soil is a Function of Sensing System over Exposed Soil is a Function of Electromagnetic Energy from Several SourcesElectromagnetic Energy from Several Sources

Total Upwelling Radiance (Total Upwelling Radiance (LLtt) Recorded by a Remote ) Recorded by a Remote

Sensing System over Exposed Soil is a Function of Sensing System over Exposed Soil is a Function of Electromagnetic Energy from Several SourcesElectromagnetic Energy from Several Sources

•• soil texture (percentage of sand, silt, and clay),soil texture (percentage of sand, silt, and clay),•• soil moisture content (e.g. dry, moist, saturated),soil moisture content (e.g. dry, moist, saturated),•• organic matter content,organic matter content,•• iron-oxide content, andiron-oxide content, and•• surface roughness.surface roughness.

•• soil texture (percentage of sand, silt, and clay),soil texture (percentage of sand, silt, and clay),•• soil moisture content (e.g. dry, moist, saturated),soil moisture content (e.g. dry, moist, saturated),•• organic matter content,organic matter content,•• iron-oxide content, andiron-oxide content, and•• surface roughness.surface roughness.

Spectral Reflectance Characteristics of Spectral Reflectance Characteristics of SoilsSoils Are a Function of Several Important CharacteristicsAre a Function of Several Important Characteristics

Spectral Reflectance Characteristics of Spectral Reflectance Characteristics of SoilsSoils Are a Function of Several Important CharacteristicsAre a Function of Several Important Characteristics

In situIn situ Spectroradiometer Reflectance Spectroradiometer Reflectance Curves for Dry Silt and Sand SoilsCurves for Dry Silt and Sand Soils

In situIn situ Spectroradiometer Reflectance Spectroradiometer Reflectance Curves for Dry Silt and Sand SoilsCurves for Dry Silt and Sand Soils

20

60

100P

erce

nt R

efle

ctan

ce

0.5 0.7 1.1 1.30

Wavelength (m)

80

40

0.9 1.5 1.7 1.9 2.1 2.3 2.5

Silt

Sand

10

30

50

70

90

20

60

100P

erce

nt R

efle

ctan

ce

0.5 0.7 1.1 1.30

Wavelength (m)

80

40

0.9 1.5 1.7 1.9 2.1 2.3 2.5

Silt

Sand

10

30

50

70

90 P

erce

nt

Ref

lect

ance

Wavelength (m)

Radiant energy may be reflected from the Radiant energy may be reflected from the surface of the dry soil, or it penetrates into the surface of the dry soil, or it penetrates into the soil particles, where it may be absorbed or soil particles, where it may be absorbed or scattered. Total reflectance from the dry soil is scattered. Total reflectance from the dry soil is a function of specular reflectance and the a function of specular reflectance and the internal volume reflectance.internal volume reflectance.

Radiant energy may be reflected from the Radiant energy may be reflected from the surface of the dry soil, or it penetrates into the surface of the dry soil, or it penetrates into the soil particles, where it may be absorbed or soil particles, where it may be absorbed or scattered. Total reflectance from the dry soil is scattered. Total reflectance from the dry soil is a function of specular reflectance and the a function of specular reflectance and the internal volume reflectance.internal volume reflectance.

specular reflectance

incident energy

interstitial air space

specular reflectance

soil water

a.

b.

dry soil

wet soil

volume reflectance

specular reflectance

incident energy

specular reflectance

incident energy

interstitial air space

specular reflectance

soil water

a.

b.

dry soil

wet soil

volume reflectance

specular reflectance

incident energy

As soil moisture increases, each soil particle As soil moisture increases, each soil particle may be encapsulated with a thin membrane of may be encapsulated with a thin membrane of capillary water. The interstitial spaces may capillary water. The interstitial spaces may also fill with water. The greater the amount of also fill with water. The greater the amount of water in the soil, the greater the absorption of water in the soil, the greater the absorption of incident energy and the lower the soil incident energy and the lower the soil reflectance.reflectance.

As soil moisture increases, each soil particle As soil moisture increases, each soil particle may be encapsulated with a thin membrane of may be encapsulated with a thin membrane of capillary water. The interstitial spaces may capillary water. The interstitial spaces may also fill with water. The greater the amount of also fill with water. The greater the amount of water in the soil, the greater the absorption of water in the soil, the greater the absorption of incident energy and the lower the soil incident energy and the lower the soil reflectance.reflectance.

Reflectance from Dry versus Wet SoilsReflectance from Dry versus Wet SoilsReflectance from Dry versus Wet SoilsReflectance from Dry versus Wet Soils

Higher moisture content in (a) Higher moisture content in (a) sandy soil, and (b) clayey soil sandy soil, and (b) clayey soil results in decreased reflectance results in decreased reflectance throughout the visible and near-throughout the visible and near-infrared region, especially in infrared region, especially in the water-absorption bands at the water-absorption bands at 1.4, 1.9, and 2.7 1.4, 1.9, and 2.7 m. m.

Higher moisture content in (a) Higher moisture content in (a) sandy soil, and (b) clayey soil sandy soil, and (b) clayey soil results in decreased reflectance results in decreased reflectance throughout the visible and near-throughout the visible and near-infrared region, especially in infrared region, especially in the water-absorption bands at the water-absorption bands at 1.4, 1.9, and 2.7 1.4, 1.9, and 2.7 m. m.

Reflectance from Moist Reflectance from Moist Sand and Clay SoilsSand and Clay Soils

Reflectance from Moist Reflectance from Moist Sand and Clay SoilsSand and Clay Soils

20

60

Per

cent

Ref

lect

ance

0.5 0.7 1.1 1.30

40

0.9 1.5 1.7 1.9 2.1 2.3 2.5

22 – 32%

10

30

50

Sand

20

60

0.5 0.7 1.1 1.30

Wavelength (m)

40

0.9 1.5 1.7 1.9 2.1 2.3 2.5

35 – 40% 10

30

50 2 – 6%

0 – 4% moisture content

5 – 12%

Clay

a.

b.

Per

cent

Ref

lect

ance

20

60

Per

cent

Ref

lect

ance

0.5 0.7 1.1 1.30

40

0.9 1.5 1.7 1.9 2.1 2.3 2.5

22 – 32%

10

30

50

Sand

20

60

0.5 0.7 1.1 1.30

Wavelength (m)

40

0.9 1.5 1.7 1.9 2.1 2.3 2.5

35 – 40% 10

30

50 2 – 6%

0 – 4% moisture content

5 – 12%

Clay

a.

b.

Per

cent

Ref

lect

ance

P

erce

nt

Ref

lect

ance

P

erce

nt

Ref

lect

ance

SandSandSandSand

ClayClayClayClay

Generally, the greater Generally, the greater the amount of organic the amount of organic content in a soil, the content in a soil, the

greater the absorption greater the absorption of incident energy and of incident energy and the lower the spectral the lower the spectral

reflectancereflectance

Generally, the greater Generally, the greater the amount of organic the amount of organic content in a soil, the content in a soil, the

greater the absorption greater the absorption of incident energy and of incident energy and the lower the spectral the lower the spectral

reflectancereflectance

Organic Organic Matter in a Matter in a Sandy SoilSandy Soil

Organic Organic Matter in a Matter in a Sandy SoilSandy Soil

Iron oxide in a sandy Iron oxide in a sandy loam soil causes an loam soil causes an

increase in reflectance increase in reflectance in the red portion of in the red portion of

the spectrum (0.6 - 0.7 the spectrum (0.6 - 0.7 m) and a decrease in m) and a decrease in in near-infrared (0.85 - in near-infrared (0.85 - 0.90 0.90 m) reflectancem) reflectance

Iron oxide in a sandy Iron oxide in a sandy loam soil causes an loam soil causes an

increase in reflectance increase in reflectance in the red portion of in the red portion of

the spectrum (0.6 - 0.7 the spectrum (0.6 - 0.7 m) and a decrease in m) and a decrease in in near-infrared (0.85 - in near-infrared (0.85 - 0.90 0.90 m) reflectancem) reflectance

IronIron Oxide in a Oxide in a Sandy Loam SoilSandy Loam SoilIronIron Oxide in a Oxide in a

Sandy Loam SoilSandy Loam Soil