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Proceedings of the Symposium on Global and Environmental Monitoring

C.A. Hutton
1525 Carling Ave.
Ottawa, Ontario
R.J. Brown
Canada Centre for Remote Sensing
1547 Merivale Rd.
Ottawa, Ontario
M.G. Lowings
Polar Sea Research
204, 740 - 4 Avenue South
Lethbridge, Alberta
Soil salinity is an increasing problem in the
Canadian prairies. Irrigation, in addition to many
popular farming practices such as summerfallowing
have increased and intensified the problem. Since
land reclamation is difficult and expensive remote
sensing offers a potential tool with which to monitor
the problem and allow more accurate and timely
remedial measures. Since areas of salinity will move,
shift, be introduced or increase in severity, as
changes occur in the rainfall and groundwater
patterns, an adequate monitoring method becomes
Previous efforts to identify saline soils with VIR
data have indicated some intermediate to mature
saline seeps can be detected by salt crusting or
identification of indicator plant species.
(Chaturvedi, L., et al., 1983; Dalsted, K.J., 1979)
Since, SAR offers a unique interaction with ground
targets, the potential for identification of saline
areas and their severity is unknown. SAR data was
acquired over an area surrounding the town of
Warner, in southern Alberta to assess its potential
for mapping and monitoring salinity. The objectives
of the present work were to assess 1) the capability
of SAR data for saline area identification and 2)
determine the potential for mapping the severity of
these areas.
C and X-Band narrow mode HH data was acquired in
July while both HH and VV were collected in October
of 1989. The July data were analyzed to locate
saline areas through varied backscatter related to
salt crusts (or chemical variations in the soil) or
differing dielectric constants which might indicate
less severe areas. In vegetated areas a reduction
in crop health, identified through reduced
backcscatter, hopefully will correlate with salinity.
Using the October data set, collected after harvest,
the indicators of salt crusting were assessed in
addition to the location of two saline indicator plant
species Kochia and Foxtail. Due to the absence of
other vegetative growth (crops) these plant species
were felt to be a means of determining saline areas.
The methodology of combining the poor growth areas
on the July imagery with regions with indicator
species was developed as a means of saline
identification. The C and X-Band data were used
both to compare the information found with each
frequencies and determine a preferred frequency or
combined frequency for mapping. Also, HH and VV
were both assessed addressing any polarization
dependence that might occur.
A number of preprocessing tasks were carried out
in preparation of this data analysis. The data were
radiometrically corrected to remove the antenna
pattern effects and were filtered with a 5x5 median
filter to remove the speckle. The data were
stretched to fill the entire dynamic range or
enhanced to provide the greatest visual contrast
between the features on these images. Negatives
were created from these data and reproduced
photographically at an enlarged scale for use in the
analysis. The analysis was conducted qualitatively
in the first stages using photo interpretation but
will be expanded to include digital methods at a
later data.
A SUN system running the PCI EASI/PACE software,
was used to carry out the preprocessing. A
Compaq-base EASI/PACE package and a PAMAP GIS
package was used to conduct the mapping portions
of this experiment. A map was produced identifying
the crop types and medium and severe saline areas.
The salinity information was digitized from a Soil
survey of the County Warner, Alberta, 1984.
Using the saline map and field overlay, the ability
to identify these known saline areas were
determined. The factors influencing the radar
backscatter such as crop type, topography and
hopefully salinity were assessed. The regions of
known salinization were assessed to determine
whether the SAR could identify these and map any
changes which have occurred.
Outputs from the analysis will include maps
indicating saline areas derived from the SAR
imagery and, SAR/VIR imagery in combination. The
mapping potential of the SAR data set in reference
to frequency, polarization, incidence angle and date
are discussed.
Chaturvedi, L., K.R. Carver, J.C. Harlan, G.D.
Hancock, F.V. Small and K.J. Dalstead, 1983,
"Multispectral Remote Sensing of Saline Seeps", IEEE
Transactions on Geoscience and Remote Sensing, Vol.
GE-21. No. 3, pp 239-250.