Agriculture Reference
In-Depth Information
For example, a FieldSpec HandHeld portable spectroradiometer (Analytical Spectral
Devices, Inc., Denver, CO) acquires a continuous spectrum by measuring radiation
intensity in 512 bands between 325 and 1075 nm. The FieldSpec 3 portable spec-
trometer from the same company can take measurements from 350 to 2500 nm with
sampling intervals of 1.4 nm at 350-1000 nm and 2 nm at 1000-2500 nm. Ground-
based spectroradiometers have been widely used in precision agriculture for estimat-
ing soil properties (Sudduth and Hummel, 1993a; Thomasson et al., 2001), assessing
crop nitrogen status (Buscaglia and Varco, 2002; Zhao et al., 2005), and detecting
crop pests (Mirik et al., 2007; Liu et al., 2010).
Imaging sensors are designed to provide views of a target area from vertical
(nadir) perspectives. Aerial photography is the oldest and simplest form of remote
sensing and provides film-based photographs with very fine spatial resolution, but it
has been gradually replaced by continuing innovations in digital imaging technol-
ogy. Electro-optical sensors are the main imaging sensors being used today. These
sensors use detectors to convert the reflected and/or emitted radiation from a ground
scene to proportional electrical signals, which are then recorded on magnetic, opti-
cal, and/or solid-state media and can be viewed as two-dimensional images on a
computer or television monitor. Electro-optical imaging systems are capable of oper-
ating in numerous bands from more spectral regions of the electromagnetic spec-
trum, including near-ultraviolet, VIS, NIR, MIR, and thermal infrared.
4.2.6.2 Airborne Multispectral and Hyperspectral Imaging Systems
The growing interest in airborne remote sensing was stimulated by research and
development on multispectral imaging systems and their applications in the 1980s
and 1990s (Meisner and Lindstrom, 1985; Pearson et al., 1994; Everitt et al., 1995).
The increased use of this technology was attributed to its low cost, high spatial reso-
lution, immediate availability of imagery for visual assessment, compatibility with
computer processing systems, and ability to obtain data in narrow spectral bands
in the VIS to MIR region of the spectrum (Mausel et al., 1992; King, 1995). Most
airborne digital imaging systems can provide multispectral image data at spatial
resolutions ranging from less than 1 m to a few meters and at 1 to 12 narrow spectral
bands in the VIS to NIR regions of the electromagnetic spectrum (Pearson et al.,
1994; Escobar et al., 1998; Yang, 2010). Airborne multispectral imagery has been
widely used in precision agriculture assessing soil variability (Barnes et al., 2003),
mapping crop growth and yield variability (Yang and Anderson, 1999; Pinter et al.,
2003; Inman et al., 2008), and detecting crop insect and disease infestations (Moran
et al., 1997; Yang et al., 2005; Franke and Menz, 2007; Backoulou et al., 2011).
Most airborne multispectral imaging systems use multiple charge-coupled device
(CCD) cameras, each of which is equipped with a different bandpass filter. This
approach has the advantage that each camera can be individually adjusted for opti-
mum focus and aperture settings, but has the disadvantage that the images from all
bands have to be properly aligned. One such system is a four-camera multispec-
tral imaging system assembled at the USDA-ARS kika de la Garza Subtropical
Agricultural Research Center in Weslaco, TX. The multispectral system consists
of four high-resolution CCD digital cameras and a ruggedized PC equipped with
a frame grabber and image acquisition software. The cameras are sensitive in the
