Agriculture Reference
In-Depth Information
position, and altitude. The sensor integrates solid state gyros and GPS with a real-
time Kalman filter for increased accuracy.
4.2.6.3 Satellite Imaging Systems
Satellite remote sensing systems not only cover large surface areas on the earth,
but also view the same target area repeatedly. Traditional satellite systems such as
Landsat and SPOT have been widely used for agricultural applications over large
geographic areas, but this type of imagery has limited use for precision agricul-
ture because of its coarse spatial resolution. Remote sensing from space is rapidly
changing with many countries and commercial firms developing and launching new
systems on a regular basis. Commercial availability of high-resolution satellite sen-
sors (i.e., IKONOS, QuickBird, GeoEye-1, and WorldView-2) has opened up new
opportunities for mapping within-field variability for precision agriculture. These
satellite sensors have significantly narrowed the gap in spatial resolution between
satellite and airborne imagery. IKONOS and QuickBird imagery has been evaluated
for assessing soil properties (Sullivan et al., 2005), estimating crop leaf nitrogen
content (Bausch et al., 2008), and mapping crop yield variability (Chang et al., 2003;
Dobermann and Ping, 2004; Yang et al., 2006).
When GeoEye, Inc. (Herndon, VA) successfully launched the IKONOS satellite in
1999, it made history with the world's first high-resolution commercial remote sensing
satellite for civilian uses. IKONOS provides 1-m panchromatic images in the 0.45- to
0.90-
μ
m spectral range and 4-m multispectral imagery in the blue (0.45-0.52
μ
m),
green (0.51-0.60
m) bands. The pan-
chromatic and multispectral imagery can be merged to create 1-m color imagery (pan-
sharpened). The radiometric resolution is 11 bits, or 2048 gray levels. The image swath
is 11.3 km at nadir, and the revisit time is less than 3 days. Shortly after the successful
launch and operation of IKONOS, DigitalGlobe, Inc. (Longmont, CO) launched the
QuickBird satellite in 2001. QuickBird provides panchromatic and multispectral data
in essentially the same spectral ranges as those of IKONOS, but at a higher spatial
resolution. QuickBird acquires panchromatic data with 0.60-m resolution and four
multispectral bands with 2.4-m resolution. Similarly, pixel depth is 11 bits. The image
swath at nadir is 16.4 km, and the sensor can tilt up to 45° off nadir.
GeoEye again made history with the launch of GeoEye-1 in 2008. It offers unprece-
dented spatial resolution by simultaneously acquiring 0.41-m panchromatic and 1.65-m
four-band multispectral imagery. The spectral ranges are similar to those of IKONOS.
The pixel dynamic range is also 11 bits. The image swath is increased to 15.2 km.
On October 8, 2009, DigitalGlobe launched WorldView-2, the first high-resolution
eight-band multispectral satellite, to acquire panchromatic data at 0.46-m resolution
and multispectral imagery at 1.84-m resolution. WorldView-2's unique combination of
high spatial and spectral resolution provides new opportunities and potential for a vari-
ety of practical remote sensing applications. The imagery is distributed at either 0.5- or
0.6-m resolution for the panchromatic band and at either 2.0- or 2.4-m resolution for
the multispectral bands, depending on the sensor's viewing angle. The image swath at
nadir remains at 16.4 km, and the average revisit time is about 1.1 days. Table 4.1 gives
the spectral characteristics for the four high-resolution satellite sensors.
μ
m), red (0.63-0.70
μ
m), and NIR (0.76-0.85
μ
