Agriculture Reference
In-Depth Information
radiometric temperature sensing, photometric sensors with bands in the visible
(400-700 nm) and near-infrared (NIR; 700-1500 nm) range for estimating crop bio-
physical properties (Table 11.1).
In the case of moving sprinkler irrigation systems, it is ideal to use the system lateral
as a platform for remote sensing. Mounting IRTs onto a pivot lateral has allowed for crop
water stress monitoring (Sadler et al. 2002; Wanjura et al. 2006) and automatic irrigation
scheduling of corn, soybean (Peters and Evett 2008), and cotton (O'Shaughnessy and
Evett 2010a) using plant-feedback algorithms. For robust monitoring of crop canopy, it
is recommended that a minimum of two sensors be mounted at either border of an area
of interest, facing inward and forward-looking of the irrigation spray, at an oblique angle
to reduce sun angle effects by averaging temperatures from sunlit and shaded sides of
the canopy. The oblique angle reduces sensor viewing of soil background in the case of
row crops and a less than full canopy. Because the sprinkler system passes over different
areas at different times of the day, a method to estimate diel canopy temperature,
T
s
, of
a specific area is required. The scaling procedure described by Peters and Evett (2008)
estimates canopy temperature dynamics using a one-time-of-day measurement:
(
)
(
)
TTTT
TT
−
−
rmt,t
e
ref
e
TT
=+
(11.5)
s
e
−
Tref,t
e
where
T
e
(°C) is the predawn canopy temperature;
T
ref
(°C) is the reference canopy
temperature at the same time interval as
T
s
(°C) (i.e., 13:00 CST);
T
rmt,t
is the one-
time-of-day canopy temperature measurement at the plot (remote location, denoted
by subscript rmt) at any daylight time
t
measured by the IRTs on the pivot lateral; and
T
Tref,t
(°C) is the measured reference temperature for the time
t
that the area (remote)
TABLE 11.1
Field-Based Sensors, Typical Measurements, and Utility for Automating
Irrigation Scheduling
Sensor Type
Measurement
Utility
Geographical positioning unit
WAAS corrected latitude and
longitude
Spatial location in field
Infrared thermometers
Surface radiometric temperature
Assess crop water stress
Microclimatological
Relative humidity, air temperature,
solar irradiance, wind speed
Predict irrigation timing
Approximate irrigation amount
Spectral radiometer
Spectral reflectance
Estimate crop coefficients
Disease, weed, pest detection
Estimate plant biophysical
properties
Rain gauge
Precipitation
Terminate irrigation if rainfall
is above a minimum threshold
Estimate daily soil water
balance
