During the 1969 and 1970 growing seasons research was conducted to investigate the relationship between remote sensing imagery and soil moisture. The research was accomplished under two completely different conditions: (1) cultivated cropland in east central South Dakota, and (2) rangeland in western South Dakota. Aerial and ground truth data are being studied and correlated in order to evaluate the moisture supply and water use. Results show that remote sensing is a feasible method for monitoring soil moisture

Schmer, F. A.

Waltz, F. A.

Werner, H. D.

English

NASA Technical Reports Server

SECTION 1+9 Hydrology
SUMMARY — REMOTE SENSING SOIL MOISTURE RESEARCH
December 1970
by
Fred A. Schmer, Hydrologist
Hal D. Werner, Research Assistant
Fred A. Waltz, Data Handling
Remote Sensing Institute
South Dakota State University
Brookings, South Dakota 57006
INTRODUCTION
Knowledge of soil moisture conditions is of prime
importance to the management of water resource systems.
Remote sensing may be able to provide considerable additional
information to our water resource managers. Of special
concern to agriculture is the ability to evaluate soil
moisture conditions in order to enhance our production
potential.
During the 1969 and 1970 growing seasons research was
conducted to investigate the relationship between remote
sensing imagery and soil moisture. The research is being
accomplished under two completely different conditions; (1)
cultivated cropland in east central South Dakota and, (2)
rangeland in western South Dakota. Aerial and ground truth
data are being studied and correlated in order to evaluate
the moisture supply and water use. Results show that remote
sensing is a feasible method for monitoring soil moisture.
RESEARCH UNDER CULTIVATED CROPLAND CONDITIONS
1969 RESEARCH EFFORT
Methodology
The study area for the cultivated cropland condition was
located on the South Dakota State University Redfield
Irrigation Farm in north central South Dakota. In 1969 soil
moisture was studied on various crops on the irrigated part
https://ntrs.nasa.gov/search.jsp?R=19720004649 2020-03-23T13:27:27+00:00Z
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of the experimental farm. The experiment was designed on the
basis of correlating data from sensors on repetitive flights
with data taken on the ground. Sensors which were flown
include the optical mechanical thermal scanner, the gang of
four Hasselblads, and the precision radiation thermometer.
Least squares analysis of variance was computed on optical
density data as read by a Macbeth densitometer. Days, as a
source of variation, was very significant, as were crops and
days by crops.
Results and Conclusions
Conclusions drawn were that extraneous variation, namely
varying levels of incoming radiation and film processing,
affected the optical density to a large extent. Regression
analyses on a within day basis yielded large r2 values of
•95 to .97 for each of the days in question.
Simple correlations between Ektachrome infrared optical
density and the moisture profile were .7 using a neutral
filter, .7 with the red filter, and .02 using the green
filter. This leads to the conclusion that in the tri-layered
film, the infrared layer was most effective in delineating
the moisture profile. However, in the Ektachrome MS film the
correlations were .5 to .7 for all four filters. The thermal
relationship to depth profile was .021 or extremely low.
This occurred in the corn field and leads to the conclusion
that the corn canopy effectively destroyed the correlation
between the thermal optical density and the depth profile
or moisture profile. However, the opposite occurred when
the area was fallowed. The correlation between thermal and
the moisture profile was .857 in the fallow field. This
leads to the conclusion that thermal scanning in the infrared
region is highly useful for delineating soil moisture where
no crop canopy exists to destroy its affect. However,
Ektachrome infrared film is superior where there exists a
viable crop canopy and should be used in this manner.
1970 RESEARCH EFFORT
Methodology
In 1970 the study area was reduced in size, different
soil moisture conditions were included by the addition of
irrigated and non-irrigated plots, and only one crop, grain
sorghum, was used. Besides the irrigated and non-irrigated
sorghum, a fallow plot was incorporated into the design as
a reference. The field experimental setup is given in
Figure 1.
Detailed ground truth data from the field were collected,
including soil moisture by soil sample and neutron scattering,
soil tension, crop and soil conditions, 35 mm ground photos,
incoming and net radiation, and intensive weather data such
as rainfall, wind, and temperature. Most of these were
directly recorded in digital form.
Aerial data collection was planned in order to correlate
closely with data collection from the future EROS projects.
The film-filter combinations used correspond to the same
general segments of the spectrum as the ERTS satellites. One
color and three black and white films were used. Color
reversal film was used with three-layer response in the green,
red, and near-infrared regions of the spectrum. The black
and white films were filtered for corresponding bands. A
thermal scanner provided infrared imagery in the region from
l\.^>\im to 5.5]_im. Incoming and reflected radiation was
recorded generally by three solameters filtered in the green,
red, and near-infrared portions of the spectrum. In addition,
specific weather conditions relating to cloud and haze
conditions were recorded at the time of each overflight.
Both aircraft and ground truth missions were scheduled
so that the data taken would be most effective in analyzing
changes in soil moisture. Missions were planned as soon
before and after irrigations as possible and at other
critical times of soil moisture and plant maturity. Thirteen
aerial missions were flown in 1970 from shortly after plant
emergence until just before harvesting of the sorghum.
Plight altitudes were at 1000, 2000, and 5000 feet above
ground level. Ground truth was collected during each over-
flight and at other selected times.
Imagery analyses are presently being performed by three
methods: (1) visual interpretation, (2) film density
measurements, and (3) use of a color encoding film density
analysis system specifically designed for imagery
interpretation. The timing of this report is such that data
analysis has not been completed. However, visual observation
of the imagery does allow interpretation of moisture
differences during periods of plant stress.
U9-1*
Final analysis will be accomplished by correlation of
film densities, and the output from the color encoding
density analysis system, with the ground truth data. The
overall difference between the total soil moisture supply
within the irrigated and non-irrigated sorghum was smaller
than expected. Soil moisture differences were substantial
in the upper two feet of the profile, but the differences
tended to disappear with increasing depth in the profile.
The presence of this subsurface moisture could be attributed
to the fact that the area with non-irrigated sorghum had
been irrigated in preceeding years. Therefore, the non-
irrigated sorghum was never severely stressed. Yield results
of 7375 pounds per acre for irrigated and 5766 pounds per
acre for non-irrigated, or only 21.8 percent difference,
supports this theory.
Results
The preliminary results indicate that the soil-crop
combination can provide information as to the changing
moisture conditions throughout the season. Imagery analyses
appear to show that the sorghum will provide an adequate
indication of the available soil moisture. While the
spectral reflectance of the soil seems to indicate only
surface moisture, the crop relates moisture conditions of
the soil profile, especially with increased plant maturity.
RESEARCH UNDER RANGELAND CONDITIONS
1970 RESEARCH EFFORT
Water resources is of prime importance to range manage-
ment. The location and management of water in range areas
is many times the ultimate control of stock numbers.
Availability of soil moisture is the determining factor in
range production. Therefore, during the 1970 growing season
a research effort on rangeland conditions in western South
Dakota was initiated. In this research effort we are
concerned with the delineation of water resources in
rangeland.
Methodology
This research effort is being conducted on the South
Dakota State University Cottonwood Range Field Station. This
49-5
experimental station comprises approximately 2,640 acres
located in west central South Dakota approximately 75 miles
east of Rapid City. Figure 2 depicts the layout of the
experimental station. The six summer pastures are the area
of interest in this study.
This research, is being accomplished as a cooperative
effort with the Animal Science Department at South Dakota
State University. The ground truth data to be utilized in
the analysis of the remote sensing data are being collected
by other active research projects at the station. The
collection of ground truth data has been fully coordinated
with the collection of remote sensing data.
'Biweekly soil moisture data are being collected with a
neutron probe to a depth of at least four feet and gravimetric
sampling is also being utilized at the shallower depths. Soil
temperatures to a depth of 150 cm are obtained daily.
Evaporation from a standard weather bureau evaporation pan,
maximum and minimum temperatures, continuous recording of
humidity and.temperature in a standard weather bureau shelter,
wind velocity and solar and sky radiation are being recorded.
Precipitation is measured with a standard weather bureau
recording rain gage. Soils are being described including
mechanical analysis, moisture release curves, bulk density,
soil organic matter and exchangeable cations by horizons.
Above ground biomass is being determined at two week
intervals during the period of rapid growth from approximately
May 15 to August 15 and at approximately monthly intervals
during the remainder of the year except when snow cover
prevents sampling. Below ground herbage biomass is being
determined at monthly intervals during the period of active
growth and' at two month intervals the remainder of the year
except when frozen soil or snow cover prevents sampling.
Remote sensing data collection missions were made on
June 9, 1970, July 7, 1970, August 4, 1970 and September 3,
1970. No data were obtained on the August 4, 1970 mission
because of unfavorable cloud conditions. The missions were
scheduled during the time period when below herbage biomass
was being collected (all other data were also collected at
this time) in order to obtain the maximum amount of ground
truth data during the approximate time of the overflight.
Multispectral imagery compatable with the ERTS A and B
film-filter combinations, reflective and incoming radiation
data and thermal scanner imagery were scheduled to be
collected on each mission.
U9-6
Imagery Analysis
Analysis of the first year data will be primarily
directed toward interpretation of the remote sensing data as
it relates to grazing conditions and available soil moisture.
Densitometer measurements obtained with a Macbeth Model
TD-404 densitometer, and soil moisture data, will be
statistically analyzed. A Spatial Data Systems color
encoding system will be utilized in interpreting the imagery
for grazing conditions and soil moisture. The various remote
sensing imagery collected will be evaluated for its
effectiveness in determining the resource management factors
under study.
Due to the limited amount of available processed ground
truth data no detailed analysis of the data has been
accomplished as of the writing of this report. However,
some visual relationships are evident. As time progresses
during the summer season the effect of grazing intensity is
evident. Ungrazed areas in pastures 2 and 4 are also easily,
identified. The black and white imagery with the green
filter (number 58) and the color infrared imagery show the
grazing practice differences quite well. Pastures 1 and 4
have been heavily grazed, pastures 2 and 5 moderately grazed,
and pastures 3 and 6 lightly grazed. Figure 3 is an
example of the imagery collected. Figure 3 is a print made
from black and white Plus-X film filtered with a 25A
Wratten filter. Soil type differences are best identified
on the black and white film with "the red filter (25A) and
these data will be fully interpreted at a later date with
the available soils survey of the area.
Results
Preliminary results from the remote sensing data are
quite encouraging. Different grazing intensities are quite
evident on the imagery. Considerable analysis needs to be
accomplished before any conclusions and/or recommendations
can be made. The ground truth data and the remote sensing
data will be statistically analyzed as soon as the ground
truth data is available. The Spatial Data Systems color
encoding system will be used for the soil type study and the
aerial moisture distribution study.
U9-T
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irrigated sorghum connected
Scale Hn = 125ftTens io meter Plots-
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Fieure 1. Experimental ground setup for remote sensing soil
moisture research under cultivated cropping conditions.
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HIGHWAY 14-16
Fieure 2. South Dakota State University Cottonwood Range
Field Station, Cottonwood, South Dakota.
Figure 3. Six summer pastures on South Dakota State
University Cottonwood Range Field Station printed from
black and white 70 mm Plus-X filtered with a 25A filter,


Summary: Remote sensing soil moisture research

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