A ground study conducted utilizing hand held radiometers to collect visible, near infrared and thermal infrared measurements. The data was analyzed and evaluated in terms of the ground measurements, which included percent crop canopy cover. The results used to recommend future action regarding use of satellite data in irrigation management

Heilman, J.

Moore, D.

Myers, V.

English

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REPORT TYPE:	 Semi-Annual Report #1
SUBMITTED TO:
	 National Aeronautics and Space Administration
Goddard Space Flight Center
Greenbelt, Maryland 20771
SUBMITTED BY:	 RE!iote Sensing Institute
South Dakota State University
Brookings, South Dakota 57007
INVESTIGATORS:
	 Jim Heilman, Donald Moore, and Vic Myers
GRANT NUMBER:	 NAG 5-37
BACKGROUND
A grant was established 4/1/80 with the long term objec-
tive to test the utility of thermal and reflective data for pre-
dicting crop coefficients and soil moisture as inputs into the
U.S. Water and Power Resource Service (formerly U.S. Bureau of
Reclamation) irrigation scheduling program. The grant proposal
was in response to RTOP 677-22-23 entitled Irrigation Scheduling.
A ground study utilizing hand-held radiometers was to be
conducted at the Navajo Indian Irrigation project near Farmington,
New Mexico in conjunction with ongoing USW&PkS measurements in-
cluding lysimetric measurements of evapotranspiration. The
Remote Sensing Institute was to collect visible, near IR and
thermal IR measurements to be analyzed and evaluated in terms
of the ground measurements which included percent crop canopy
cover obtained by RSI. Results were to be used to recommend
future action regarding use of satellite data in irrigation
management.
PROGRESS TO DATE
Introduction
RSI conducted a field measurement program during the summer
of 1980. Measurements were made with two visible/near IR hand-
held radiometers and a hand-held thermal radiometer. Soil mois-
ture and lysimetric measurements were collected by USW&PRS per-
sonnel and forwarded to RSI along with meteorological data. All
the data are described in detail in the next section of the report.
Analysis has been completed on the visible/near IR radiometer
measurements in conjunction with the moisture and canopy cover data.
Analysis is presently underway on the thermal IR data.
Field Measurements
The study was conducted on the Navajo Indian Irrigation Pro-
ject near Farmington, New Mexico, in conjunction with a Water and
Power Resource Service water use study. The test site consisted
of four alfalfa plots with lysimeters that were irrigated with a
line source sprinkler. The line source linearly decreases the
amount of water applied as the distance from the source increases.
With the configuration of the system, plot 1 was over-irrigated,
plot 2 received optimum applications, and plots 3 and 4 were under-
irrigated.
Radiances from each plot were measured with Mark II three-band
and EXOTECH four-band radiometers in the mid-morning (1000-1100 MDT)
and early afternoon (1300-1400 MDT). Radiances were converted to
reflectances using radiance measurements of reference panels coated
with 3•M white Nextel paint and BaSo 4 . Panel radiances were measured
before and after each plot measurement. Radiometric temperatures
of the plots were measured with a PRT-5 within the same time frame.
Radiances of bare soil were also measured.
Surface soil water contents (0-4 cm) were determined gravi-
metrically on samples collected at the same time as the spectral
measurements. Percent canopy cover was determined using 35min color
slides (photographed from a vertical position) projected on a
random dot grid. All measurements began after the second cutting
of alfalfa in early July 1980 and continued to maximum canopy
cover.
Water and Power (USW&PRS) personnel collected profile soil
moisture (neutron attenuation method) and lysimetric measurements
of actual evapotranspiration. Meteorological data they collected
included maximum and minimum air and dew point temperatures, solar
radiation, wind speed, and pan evaporation. USW&PRS calculated
potential ET using the P Ar : ian equation which was calibrated for the
climatic conditions at I rmington.
Preliminary Results
The scheduling procedure used by Irrigation i4a nagen:ent Service
(IMS) of USW&PRS requires estimates of the crop coefficient which
is the ratio of actual to potential ET. We evaluated the relaticn-
ship between Mark II spectral measurements and the crop coefficient.
Best relationships were obtained with the perpendicular vege-
tation index (PVI) of Richardson and Wiegand (1977) using channels
1 (0.63-0.69pm) and 2 (0.76-0.901,m). The soil background line was
channel 1 = 1.03 channel 2 - 0.05
with an r 2
 of 0.89.
Figure 1 shows the relationship between PVI and the crop
coefficient for the morning rneasurenren:s. The relationship for
the afternoon measurements was not significantly different. A PVI
based on channel 2 and 3 (1.55-1.75 1 m) did not improve the results.
Ratios of channels 2 and 1, and 2 and 3 were compared with
the crop coefficient and respective r 2 of 0.791 and 0.793 were ob-
tained. The lower correlation was probably due to soil background
variations.
Preliminary results demonstrate the potential for using spec-
tral measurements to estimate the crop coefficient. Inclusion of
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a liquid water absorption channel does not appear to offer a sig-
nificant benefit.
References
Richardson, A. J. and C. L. Weigand. 1977. Distinguishing vege-
tation from soil background information. Photo. Enyr. & Remote
Sensing 12: 1541-1552.
ACTIVITIES PROJECTED THROUGH MARCH 1981
The first year activity remaining will include analysis of
the thermal IR data in relation to the crop coefficient. EXOTECH
four-band radiometer data will be evaluated for analysis, but it
is not expected that they will be analyzed due 'co problems with the
data caused by individual channel readings being saturated (off
scale on the high end) much of the time. The cause for these off-
scale readings is not known.


Irrigation management with remote sensing

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