REN R 690
Data Collection
The study site was in a quarter section of a farmers field near Lacombe, Alberta. Lacombe is located in central Alberta approximately an hour and a half south of Edmonton, Alberta. The field under investigation was approximately 10 minutes south west of the town of Lacombe.
A quad, equipped with an electromagnetic inductance sensor (EM 38 model) and a high precision GPS, drove across the field in both directions. An EMI uses electromagnetic conductivity to determine the amount of fluids in the soil (Fetter 2001). This method uses an electromagnetic field generated by a transmitter coil through which an alternating current is passed (Fetter 2001). A magnetic field is created around the coil so when the coil is placed above the ground surface, the magnetic field induces a current in the soil (Fetter 2001). The strength at which the field travels through the soil is dependent on the ground conductivity. This is a beneficial method for determining conductivity of subsurface material because it is fast and non destructive. The EM 38 measures electrical conductivity (EC) which is an indicator of soil moisture and salinity (Lahoche et al. 2010). EMI surveys are popular for delineating contaminated soils and locating underground lines.
A quad, equipped with an electromagnetic inductance sensor (EM 38 model) and a high precision GPS, drove across the field in both directions. An EMI uses electromagnetic conductivity to determine the amount of fluids in the soil (Fetter 2001). This method uses an electromagnetic field generated by a transmitter coil through which an alternating current is passed (Fetter 2001). A magnetic field is created around the coil so when the coil is placed above the ground surface, the magnetic field induces a current in the soil (Fetter 2001). The strength at which the field travels through the soil is dependent on the ground conductivity. This is a beneficial method for determining conductivity of subsurface material because it is fast and non destructive. The EM 38 measures electrical conductivity (EC) which is an indicator of soil moisture and salinity (Lahoche et al. 2010). EMI surveys are popular for delineating contaminated soils and locating underground lines.
Digital Elevation Model
The field data collected was elevation, longitude, and latitude from the GPS and electrical conductivity(EC) from the EM38 readings. The field data was then used in a DEM (digital elevation model). A DEM is a representation of an elevation surface derived from the interpolation of irregularly spaced inputs of spatial position (Pennock and Elliott, 2003)(D-1). The output from the DEM were terrain attributes (D-2). For further information on the use of DEM contact Miles Dyck.
D-1. Digitial elevation model of field study site near Lacombe, Alberta, with sampling locations.
D-2. Sample data table with field collected data from study site near Lacombe, Alberta, and output from DEM.
Using the DEM, two main topographical characteristics can be derived: morphological and positional. Morphological attributes from the DEM to be included in the analysis are slope gradient, slope aspect, profile curvature and plan curvature. Slope gradient is the steepness of the hill slope while slope aspect is the direction the slope faces (Pennock and Elliott 2003). Steeper slopes tend to have less water infiltration and drier soils. Aspect is an important characteristic because slopes receiving more sunlight, south facing slopes, will have drier soil.
Positional attributes are profile curvature, plan curvature, specific catchment area (SCA) and specific dispersal area (SDA). Profile curvature is down slope curvature while plan is across the slope curvature (D-3). Concave slopes tends to be upper slopes while lower slopes are commonly convex. Typically concave areas at low elevation will have greater SCA while the opposite is true for SDA (Pennock and Elliott, 2003). A good way to visualize SCA and SDA is to imagine covering the entire field with marbles and then letting them roll downhill at the same time. Locations with greater SCA will collect more marbles and SDA will have no marbles.
There are no treatments for this study. The sampling units for this study are the individual measurements of EC which we are observing as well as the model output for each point. The predictor variables are the topographic attributes from the DEM output like gradient and SCA.
Positional attributes are profile curvature, plan curvature, specific catchment area (SCA) and specific dispersal area (SDA). Profile curvature is down slope curvature while plan is across the slope curvature (D-3). Concave slopes tends to be upper slopes while lower slopes are commonly convex. Typically concave areas at low elevation will have greater SCA while the opposite is true for SDA (Pennock and Elliott, 2003). A good way to visualize SCA and SDA is to imagine covering the entire field with marbles and then letting them roll downhill at the same time. Locations with greater SCA will collect more marbles and SDA will have no marbles.
There are no treatments for this study. The sampling units for this study are the individual measurements of EC which we are observing as well as the model output for each point. The predictor variables are the topographic attributes from the DEM output like gradient and SCA.
D-3. Hill slope displaying plan curvature, profile curvature, convex and concave attributes.
