Agriculture Reference
In-Depth Information
400-1000 nm spectral range and provide 2048 × 2048 active pixels with 12-bit data
depth. The four cameras are equipped with blue (430-470 nm), green (530-570 nm),
red (630-670 nm), and NIR (810-850 nm) bandpass interference filters, respectively.
Another approach to multispectral imaging is to use a beam splitting prism and
multiple CCD sensors built in one single camera to achieve multispectral imagery.
One such system is the MS4100 multispectral 3CCD camera (Geospatial Systems,
Inc., West Henrietta, NY), which uses a beam splitting prism and three CCD sensors
to acquire images in three to five spectral bands within the 400-1100 nm spectral
range.
Hyperspectral imaging sensors or imaging spectrometers are a new generation of
electro-optical sensors that can collect image data in tens to hundreds of very nar-
row, continuous spectral bands throughout the VIS, NIR, MIR, and thermal infrared
portions of the spectrum. These systems offer new opportunities for better differen-
tiation and estimation of biophysical attributes for a variety of remote sensing appli-
cations. Airborne hyperspectral imagery has been evaluated for characterizing soil
fertility (Bajwa and Tian, 2005), mapping crop yield variability (Goel et al., 2003;
Yang et al., 2004, 2007, 2010a; Zarco-Tejada et al., 2005), and detecting crop pests
(Fitzgerald et al., 2004; Yang et al., 2010b).
Many commercial airborne hyperspectral sensors such as AVIRIS, CASI,
HYDICE, and HyMap have been developed and used for various remote sensing
applications. Advances in CCD cameras, frame grabber boards, and modular optical
components have also led to developments of low-cost airborne hyperspectral imag-
ing systems from off-the-shelf products (Mao, 1999). A hyperspectral imaging sys-
tem assembled at the ARS Weslaco Research Center is an example of such a system
(Yang et al., 2003). The system consists of a digital CCD camera, an imaging spec-
trograph, an optional focal plane scanner, and a PC computer equipped with a frame
grabbing board and camera utility software. The CCD camera provides 1280 (
h
) ×
1024 (
) pixel resolution and true 12-bit dynamic range. The imaging spectrograph
is attached to the camera via an adapter to disperse radiation into a range of spectral
bands. The effective spectral range resulting from this integration is from 467 to
932 nm. The optional focal plane scanner can be attached to the front of the spectro-
graph via another adapter for stationary image acquisition. The horizontal and verti-
cal binning capability of the camera makes it possible to obtain images with various
spatial and spectral resolutions. For most applications, the hyperspectral sensor is
configured to capture images with a swath of 640 pixels in 128 bands.
As hyperspectral imagery is attracting more interest, more commercial airborne
hyperspectral imaging sensors have become available in recent years with improved
spatial and spectral resolutions and high performance inertial navigation systems for
increased position accuracy. For example, the AISA family of airborne hyperspec-
tral sensors from Spectral Imaging Ltd. (Oulu, Finland) includes two sensors in the
0.4- to 0.97-
ν
μ
m range (AisaEAGLE and AisaEAGLET), one sensor in the 0.97- to
2.5-
μ
m range (AisaHAWK), one sensor in the 0.4- to 2.5-
μ
m range (AisaDUAL),
and a thermal sensor in the 8- to 12-
m range (AisaOWL). The AisaEAGLE sensor
can capture images with a swath of 1024 pixels and in up to 488 bands, whereas the
AisaOWL can get a 384-pixel swath in up to 84 bands. All sensors are equipped with
a high-performance, three-axial inertial navigation sensor for monitoring the aircraft
μ
