Geography Reference
In-Depth Information
Table 1.2
Common Satellite/Platforms with key characteristics.
Sensor/Platform
Launch
Spatial Resolution
Temporal
Spectral Bands
Date
(at Nadir)
Resolution
MODIS/Terra
Dec. 1999
250m (bands 1-2)
500m (bands 3-7)
1000m (bands 8-36)
16 days
36 bands from the visual to infrared and
thermal
ASTER/Terra
Dec. 1999
15m (bands 1-3)
40m (bands 4-9)
90m (bands 10-14)
16 days
14 bands from the visual to infrared and
thermal
ETM
+
/
Landsat-7
Apr. 1999
15m Panchromatic
30m (bands 1-5
and 7)
60m (band 6)
18 days
8 bands:
Panchromatic, 3 visual, 2 infrared, 2
thermal
SPOT-5
May 2002
2.5m Panchromatic
10m (bands 1-3)
20m (band 4)
2-3 days
5 bands:
Panchromatic, 2 visual (no blue),
infrared, thermal
Ikonos
Sept. 1999
82 cm Panchromatic
3.2m Multispectral
3 days
5 bands:
Panchromatic, 3 visual, infrared
QuickBird
Oct. 2001
65 cm Panchromatic
2.62m Multispectral
2.5 days
5 bands:
Panchromatic, 3 visual, infrared
WorldView-1
Sept. 2007
50 cm Panchromatic
1.7 days
1 band:
Panchromatic
WorldView-2
Oct. 2009
50 cm Panchromatic
1.85m Multispectral
1.1 days
9 bands:
Panchromatic, 6 visual, 2 infrared,
GeoEye
Sept. 2008
50 cm Panchromatic
1.65m Multispectral
2.1 days
5 bands:
Panchromatic, 3 visual, infrared
Air Photography
N.A.
Variable. Typically 2
to 50 cm.
≈
1 day
Variable. Typically standard colour.
Most types of instruments available.
Unmanned
Aerial systems
(UAS)
N.A.
Variable. Typically 2
to 50 cm.
<
1 day
Variable. Typically small format RGB
digital cameras. Other instruments
available on large UAS.
to suggest a few data acquisition options and justify these
suggestions with the appropriate data characteristics. The
first point to note is the variable spatial resolution, for
each sensor, when images are acquired in panchromatic
mode (i.e. greyscale) and multispectral mode. It should
always be remembered that when satellite image vendors
quote a sub-metric spatial resolution, they are referring to
panchromatic imagery. At the time of writing, no satellite
platform in earth orbit can acquire multispectral imagery
with sub-metric resolutions. A possible substitute for high
resolution imagery is called 'pan-sharpened' imagery. In
a pan-sharpened image, the sub-metric resolution image
is fused with the multispectral images. This transforma-
tion uses the brightness values in the panchromatic band
to weigh the interpolation of the lower resolution mul-
tispectral bands. The result is a multispectral or colour
image with the same resolution as that of the panchro-
matic image. Another interesting point to note about
spatial resolutions is the apparent 50 cm limitation which
seems to have been reached in the more recent satellites.
In fact, the GeoEye in Table 1.2 satellite is capable of
producing 41 cm greyscale imagery and the Worldview-2
satellite can acquire at 46 cm. However, US regulations
prohibit these companies from delivering data in the
public domain with spatial resolutions below 0.5m and
therefore the images are resampled before delivery to the
customer. Unfortunately, it seems that for the foreseeable
future, satellite image spatial resolutions will be blocked
at 50 cm. In terms of temporal resolutions, these satellites
can all revisit a site within a few days. From the perspec-
tive of fluvial sciences, this makes them well suited to
seasonal monitoring. In terms of spectral resolutions, the
basic array of bands for a so-called 'multispectral' satellite
image has long been four bands in Red, Green, Blue and
Near Infrared. Many satellites in Table 1.2 conform to this
standard and have three spectral bands in the visible range
Search WWH ::
Custom Search