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Satellite
data
Concepts:
LandSat data
image bands
SPOT-5 data
reflectance
satellite sensor
mosaic
scene
panchromatic
license restrictions on SPOT data
fused data
In addition to the standard products provided for NLCD 2001 and MELCD
2004, we provide the satellite data if desired.
These are the raw data which were used to derive the other products.
LandSat data
These are currently only available on the DVD and to DEP users (in
data_layers\image_catalogs). LandSat data are 30-meter pixel data
consisting of 7 image bands
collected by NASA's LandSat 5 and LandSat 7 satellites.
A band is a range of energy reflectance
absorbed by a satellite sensor.
Reflectance is merely energy reflected off Earth and detected by a
sensor. The sensor is a machine mounted on a satellite which
detects some type of energy. The LandSat satellites utilize a
sensor called the Thematic Mapper (LandSat 5) or the Enhanced Thematic
Mapper (LandSat 7). The data provided here is for 6 of the TM or
ETM bands - 3 in visible light and 3 in infrared (bands 1-5 and 7), and
are mosaics of satellite scenes. A scene is a single
"picture" collected by the satellite, often they are merged together to
cover a large area, forming a mosaic. Four mosaics are available (maps of the dates used
are available):
Spring 2001 -
scenes collected during the early growing season after snow-melt on the
following dates: 5-7-2001, 5-8-2001*, 5-9-2001, 5-10-2001*,
5-25-2001, 5-4-2002*, 5-12-2002, 4-14-2003, 5-16-2003*,
5-17-2003. Metadata
Leaf-on 2001 -
scenes collected during the summer growing season: 8-31-1999,
5-25-2001, 6-8-2001, 6-28-2001, 7-20-2001*, 6-4-2002, 6-21-2002*,
8-9-2002. Metadata
Leaf-off 2001 - scenes
collected during the autumn season after leaves have dropped:
10-12-2000*, 10-22-2000, 9-30-2001, 10-1-2001*, 10-2-2001, 10-16-2001,
11-8-2001, 10-4-2002*, 10-12-2003*. Metadata
Leaf-on 1995 -
scenes collected (mostly) during the summer growing season for the
circa-1995 landcover: 9-25-1993*, 11-21-1993*, 8-25-1994*,
5-1-1995*, 5-31-1995*, 6-27-1995*, 7-4-1995*, 8-14-1995*, 9-6-1995*,
9-15-1995*, 8-30-1996*. Metadata
* indicates LandSat 5 data, all
others LandSat 7.
Each band of the LandSat data corresponds to a range of energy, 3 in
visible light, and 3 in infrared.
Band
Wavelength range
1
450-520nm (blue light)
2
520-600nm (green light)
3
630-690nm (red light)
4
760-900nm (near-infrared)
5
1550-1750nm (mid-infrared)
6*
10,400-12,500nm (heat emissions)
7
2080-2350nm (far-infrared)
* band 6 is a 60m band is not
included with our data. The sixth band in our data is actually
band 7.
ArcMap uses a red-green-blue display (RGB) and so only three bands can
be viewed at a time. By assigning different bands to different
colors, you can produce a variety of effects. For example bands
3-2-1 assigned to R-G-B produces a "true-color" image since visible
light is used, a 5-4-3 will produce a "false-color" image since
infrared energy is shown, but not visible to the human eye.
 
Leaf-off NLCD 2001 LandSat data
for Bangor. Left is a 3-2-1 true color image, right is a 5-4-3
false color. The false color indicates moisture and vegetation -
pink/purple are unvegetated, dark blue is water, and green indicates
vegetation.
SPOT-5 data
These data are collected by the French SPOT-5 satellite and are
currently only available to state of Maine employees and
other licensed entities. They are not available to download from
MEGIS, nor are they distributed on the MELCD 2004 DVD. The 2004
SPOT-5 data were used to refine
the NLCD 2001 data to a 5-meter resolution, and update the date
coverage for most classes to 2004. The SPOT-5 data are panchromatic meaning they only sense
a single band of visible light, creating a black-and-white image.
They are also licensed; they
can only be distributed to licensed entities. See the metadata for details and a
list of licensees.
Licensed entities may request a copy of the SPOT-5 data from the Maine Office of GIS.
The SPOT-5 data mosaic consists of 2004 scenes collected mostly during
the summer.
The same area in Bangor, shown
in SPOT-5 data. Note the much better spatial resolution due to
much smaller pixel size (5m v. 30m).
Fused data
In order to derive landcover at a 5-meter resolution, the LandSat and
SPOT data were fused, a
process also known as merging or pan-sharpening. This process
takes the pixel values from the 5-meter SPOT data and combines them
with the pixel values from the 30-meter LandSat data to come up with a
combined value using various statistical methods (which are way beyond
the scope of this class!). If you are a remote sensing analyst
with Erdas Imagine, you can download the merge model to see exactly how this was
achieved. These data are also licensed since they are
direct SPOT-5 derivatives, they fall under the same license
restrictions. They are only available on a separate set of 5 DVDs
available upon request from the Maine Office of GIS.
  
Images of a farm in Corinth, in
the Kenduskeag watershed. Left is the original 30-meter LandSat
data shown in true color (3-2-1). Center is the SPOT-5 data for
the same farm. Note the much better spatial resolution at 5
meters, but only 1 black-and-white color band. Right is the fused
product which uses the sharper edges of the SPOT-5 data combined with
the all color/energy bands of the LandSat data. This fused data
was then used to derive the MELCD 2004 landcover data.
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