the use of remote sensing for soil mapping: a review ronald vargas rojas and christian omuto...
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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!