1. Using radar for wetland mapping
Soil moisture and wetland classification
Slides modified from a presentation by Charlotte Gabrielsen for this class.

2. Southeast Arizona: Winter wet period
From C. Wang et al. 2004, Remote Sensing of Environment 90:

3. Flooding in Pakistan in 2009: Envisat SAR-based image.

4. Inundated land under forest canopy in Australia mapped using radar – water and tree trunks cause strong double backscatter.
See Australian Wetlands, Rivers and Landscapes Centre for details: (

5. Importance of Soil moisture
Commercial purposes—agriculture and irrigation
Crop-yield: pre-planting moisture; irrigation scheduling; de-nitrification
Sediment transport: runoff producing zones
Climate studies
Meteorology
Evapotranspiration: partitioning of available energy into sensible and latent heat exchange
Hydrology
Rainfall runoff: infiltration rate; water supply
Productivity often limited by either nutrient or moisture availability

6. TRADITIONAL METHODS TO MEASURE SOIL MOISTURE
Feel method
Electrical resistance
Neutron probe
Soil tension
Neutron probes contain a pellet of americium-241 and beryllium. Am-241 emits alpha particles, which collide with Beryllium and produce fast neutrons that return slow neutrons to sensor when they collide with H, which is mostly the H in water molecules.

7. Dielectric constant Dielectric constant:
Measure of the capacity of a material to store a charge from an applied electromagnetic field and then transmit the energy
The higher the dielectric constant, the less permeable a material is to radar signal
The more water there is in soil, the stronger the return signal (all other things being equal)

8. Dielectric constants for common materials
From Ken’s lecture presentation
Davis and Annan 1989;
Geological Survey Systems 1987

9. Dielectric Constant and effect of soil type
Soil dielectric constant is directly proportional to its moisture content
De Jeu et al. 2008
Relationship between soil dielectric constant and soil moisture; relationship is almost linear, except at low moisture contents
Variation of dielectric constant as a function of moisture content in sand and clay

10. soil moisture and radar signal (backscatter)
Radar signal has a linear relation with soil moisture
Zribi et al. 2005

11. Moisture content Moisture increases dielectric constant
Identical materials can look different in radar imagery due to differences in moisture content
Brightness (reflectance) of plants and surfaces increase with moisture content
Radar can penetrate deeply into dry materials but not into wet materials (quantifies 0 – 15 cm moisture)

12. Mapping soil Moisture
Timing is important because soil moisture is very dynamic
Environmental conditions and precipitation history are important
Can’t estimate in frozen soil
Depth of penetration depends on soil moisture and incidence angle and is important to understand for modeling

13. SMAP: soil moisture active passive (Launched Jan. 31, 2015!)
Provided global soil moisture and freeze thaw info with 2-3 day return time at coarse (1-3 km) spatial rez.
Radar failed July NASA looking for replacement
Passive microwaves are emitted by materials on earth (just like FIR), but they are low energy so need big pixels to get good SNR. Passive microwave emission allows measurement of temperature. Active microwaves can have smaller pixels because higher signal and can indicate water.

14. detection of wetlands
Soil moisture is a good indicator of wetland presence
High temporal resolution radar can help characterize wetland hydroperiod

15. Remote sensing of wetlands
Wetlands defined by…
Presence of water at, above, or near ground surface
Hydric soils
Vegetation species adapted to or tolerant of wet soil
Remote sensing can be used to map and monitor two of the defining wetland features, vegetation type and surface water/wet soils
Historically, wetlands have been one of the most difficult ecosystems to classify using remotely sensed data

16. Wetland ecosystem services
Flood control
Groundwater replenishment
Sediment and nutrient retention and export
Water purification
Reservoirs of biodiversity
Recreation and tourism
Climate change mitigation and adaptation
Wetlands and climate change – flood control, carbon storage (peat), etc.

17. Traditional methods for wetland mapping (NWI)
Aerial photography interpretation or single date optical imagery common source for wetland maps
Err more by omission than commission
May not represent dynamic nature of wetlands

18. Traditional methods for wetland mapping
NWI often underestimates proportion of water on the landscape
Halabisky et al. 2011

19. Sar wavelengths Commercially available SAR satellites:
L-band (~23 cm wavelength)
Useful for mapping forested and high biomass herbaceous wetlands
C-band (~5.7 cm wavelength)
Most useful in forests during leaf-off condition and for sparse canopies
X-band (~3.5 cm wavelength)
Useful for detection of water level changes

20. sar Polarization
Horizontal send and receive (HH) polarization is most useful for detecting wetlands
Cross polarizations (HV) can discriminate woody versus herbaceous vegetation types due to their sensitivity to biomass
Vertical send and receive (VV) polarization is sensitive to soil moisture and flood condition

21. Surface inundation (flooding)
Can increase radar backscatter in forests
“Double-bounce” scatter: energy emitted from sensor bounces off the water surface away from the sensor and then off a tree trunk back to sensor
But can decrease backscatter in open areas due to specular reflectance

22. Scattering of c-band energy
Bourgeau-Chavez et al. 2009

23. Radar and optical data fusion
Can improve wetland characterization by combining multiple remotely sensed data types
Uses multiple sensors
Multi-temporal data
Fusion of sensors operating in different frequencies (thermal, optical, lidar, radar, infrared) measure various aspects of wetlands for improved mapping accuracy

24. Corcoran et al. 2011

25. Study area: Plains and prairie pothole region, U.S.A

26. Stressors in the PPR Climate change Ag/Development
Truncated hydroperiod
Reduced connectivity
Images: deq.mt.gov

27. Prairie pothole region research
Using a combination of optical and radar data to map wetlands in wet and dry years to obtain information about wetland hydroperiod
For ephemeral wetlands, soil moisture is important
By determining wetland extent, aim to predict hydroperiod and wetland location for future climate change scenarios
Projections can be used to support ecological and landscape-based vulnerability assessments and climate change adaptation planning.

28. summary
Radar data has broad application for the detection of soil moisture and mapping.
Fusion of radar data with optical data can improve map accuracy.
Use of radar sensors for wetland mapping has implications for an operational wetland hydrology monitoring solution.