The Use of Remote Sensing for Soil Mapping: A Review

Ronald Vargas Rojas and Christian Omuto

Nairobi, 12th June, 2007

WHAT’S SOIL?

“Soil is the material composed of mineral particles and organic remains that overlies the bedrock and supports the growth of rooted plants”

Soil varies along the different landscapes A-B

B

A

HOW SOIL IS FORMED?

Soil Forming Factors, Jenny’s equation:

S = f (cl, o, r, p, t)S = f (cl, o, r, p, t)

S = soilcl = climateo = organisms (plant, animal and humans)r = reliefp = parent materialt = time

WHAT IS SOIL?

“Soil is considered an heterogeneous fourth dimensional body that is continuous along the landscape”.

X

Y

Z

4th dimension is time

SOIL VARIABILITY: horizontal

Soil is spatially variable in terms of x, y, z……….

Is it really soil what we are looking at?

Geographic space or spatial variability

SOIL VARIABILITY: vertical

Soil development through horizonation.

A

Btss

Bg

WHAT DO WE MAP? Soil individual vs. Soil continuum

Soil as soil body (pedon).A soil unit (mappable) polipedon.Discrete Model of Spatial Variation (polygon based).

Soil is a continuous resource in the geographic space. Continuous Model of Spatial Variation (grid)

WHAT IS A SOIL MAP?

A soil map should show the location, distribution and pattern of soils in the landscape. Needs of soil spatial data has increased for different applications.

SOIL MAPPING METHODS

Conventional soil mapping

- DMSV, polygon based mapping - Soil classes are mapped- Soil survey

+ finding soil-landscape relationship (photointerpretation of

aerial photographs or satellite images).

+ soil profile description

+ soil classification

+ soil mapping Baranja, Croatia (source: Tomislav Hengl, Msc thesis, ITC)

SOIL MAPPING METHODS

Digital soil mapping (pedometrics)

- CMSV, grid mapping (pixels).

- Implementation of Jenny equation in quantitative terms. Spatial approach.

- Different tools (geostatistics, digital terrain analysis, remote sensing, fuzzy logic, decision trees, etc) .

- Mapping mainly soil attributes.

Range of organic carbon (%) for the topsoil. Minasmy, 2006.

PRINCIPLES OF REMOTE SENSING

The principle of remote sensing

RS – Collection of information about an object without physical contact with it.

- Digital measurements of electromagnetic energy reflected/radiated by an object.

Components of RS

Object

Target Transmission Sensor

Energysource

EM radiations are used

Gamma

X-Ray

UV

VIS

Microwave

IR

Radio En

ergy in

creases

EM Spectrum

-Constant speed-Carry energy

Obstruction

RS Characteristics & potentials in soil mapping

• Polarized• Reflected• Diffracted• Attenuated• Absorbed

% R

Wavelength

Sensing windows

.. and they influence

• spatial resolution

• spectral resolution

TAXONOMY OF RS SYSTEMS

Non-imaging

Imaging

Sounding

Solar Thermal

Passive systems Active systems

IR Microwave Radiometry

A. Photo VIS/IR imaging

IR

UV sounding

Microwave Radiometry

Microwave SoundingIR

Laser & M/NIR Spectrometry

RadarMicrowave

Radar/SAR

Lidar

VIS/IR Microwave

RS radiations can be:

Sky

Earth

Sun

Sensor

Gamma

X-ray

X-ray/Gamma

Potentials and limitations of RS for soil mapping

What RS can see

• Top of the clouds• Land cover• Land surface• Soil particles/properties

Potential uses from the above detectable features

• Land cover, biomass, global circulation, soil surface

• Sea/ocean surface, soil moisture, etc.

Sky

Earth

Sun

Sensor

Limitations

• Below-clouds atmospheric dynamics

• Atmospheric attenuation, resolution,

• Penetration (vegetation and soil depth)

Important opportunities

• Integration with pedometrics

• Integration with ground sampling

• Integration of products from different types of RS

• Estimation of the Jenny’s factors

Main applications of RS in soil mapping

• Optical Systems Land cover (biomass estimation)

Soil cover or surface

Soil erosion features from high resolution images

• Radar systems Digital terrain data

Assessment of soil moisture

• Thermal systems

• Geophysical systems

Little investigated, but mainly for soil pore structure

Lithology and mineralization

How have researchers used RS in mapping soils?

• Infrared spectroscopy Janik et al. (1998); Aust. J. Exp. Agr. 38: 681-696.

Shepherd and Walsh (2002): SSSAJ: 66: 988-998

Eshel et al. (2004): SSSAJ: 68: 1982-1991

• Thermal remote sensing

VIS/NIR/MIR/NMR (laboratory, field??) for prediction of soil properties

Sullivan et al. (2004): RS & Mod. Ecos. & Sus. 5544: 566-275

Petersen et al. (1987): RSE: 23: 253-271

• Microwave RS

• Optical remote sensing

• Gamma radiometry

Engman et al. (1996). Geos. & RS. 2(27):1058-1060

Bindlish et al. (2006). RSE. 103: 127-139

Chabrillat et al. (2002). RSE. 82: 431-445 (Hyperspec)

Palacios-Orueta & Ustin (1998): RSE 65: 170-183 (AVIRIS)

• Fusion techniques

Wilford et al. (2001). AGSO J. geol & Geosp. 17: 201-216

Taylor et al. (2002). Expl. Geophys. 33: 95-102

Ricchetti (2001): IJRS, 22, 2219-2230

• Radar SRTM (DEM), GPS (position)

Mapping soil moisture, temperature, and texture

Mapping soil moisture

Mapping soil cover, land cover…..

Mapping land surface profile, DEM

Combining solar bands and microwave/RADAR

CONCLUSIONS: is RS a useful tool for soil mapping?

RS tools are very useful for soil mapping in both approaches (conventional and DSM).

The idea of using optical RS for mapping soils directly is not possible since soil development is in depth and we could see that satellite images just reflect the soil surface or land cover.

RS and Pedometrics are directly linked in generating ancillary data layers for mapping soils. Thus, they have huge potential in soil mapping.

Conventional mapping can greatly benefit from RS, especially nowadays where many different satellite images and aerial photographs are available with different spatial, spectral, and temporal resolutions.

Different unexplored fields of RS are under research and definitely promising tools for mapping soils in the near future.

The conventional soil mapping activities are critiqued for being slow and expensive. Modern soil scientists are therefore trying to develop methodologies and tools to expedite the process. However, we can conclude that RS is a good tool but direct contact with the object cannot be replaced, specially when dealing with a complex system such as soils.

THANK YOU!