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NOAA
Satellite Images
The
on-line archive contains three images for each AVHRR scene:
1. A short-wave infrared image (band 2) with land mask, latitude/longitude grid and coast
outline for showing clouds, haze and sun-glint.
2. A suspended material image from band 1, with effects of thin cloud and sun-glint reduced
using band 2. The image has cloud and land masks, the latitude/longitude grid and coast
outline.
3. A thermal image from band 4, with contrast stretched to show thermal
water patterns. The image has the cloud cover and land masks, the
latitude/longitude grid and coast outline.
Examples of NOAA near-infrared images:
Images like these are used to show patterns of cloud, haze and sun-glint and to correct
other images for their effects. In the Arctic summers they provide images of sea ice at a
time of low thermal contrast.
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| Clear Water |
Cloud/Fog/Haze |
Snow |
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VI199206240108_visi_no11.jpg
This
near-infrared image, taken at the same time as the thermal image of Vancouver Island, on
June 23,1992 at 16:05 PDT (above) shows where cloud or fog covers the water and prevents
the thermal band from showing water temperatures. On this day there is cloud offshore and
fog near Port Hardy (green to red or white). Land appears green to red. Snow is white.
Cloud-free water appears blue. |
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VI199505222100_visi_no14.jpg
This is a near-infrared image of Vancouver Island on May 22,1995 at 21:00 UTC. This
shows the locations of cloud and haze which appear here as green to red streaks and are
especially visible above the darker water, which is coloured as blue. Land appears green
to red, and white where snow lies on the coastal mountains. |
Examples of NOAA suspended
material images:
These
images show where water contains scattering particles due to river silt, plankton blooms,
or (in the Arctic) broken sea ice. The images are computed from the difference between the
signals in bands 1 and 2. Band 1 shows the signal in red light, increased by suspended
particles. Forming the difference reduces the signals due to haze, thin cloud or smoke,
and sunglint, all of which cause an almost equal increase in the two bands. Suspended
particles in water cause only a very small increase in band 2. Land shows a much higher
signal in band 2 than 1, blackening it out in the difference images. Thick cloud is also
masked to black. Since the spectral properties of different clouds vary, the differencing
is not perfect, and in many cases cloud edges appear bright, leading to possible
"false alarms" for plankton blooms. Blooms are confirmed if the pattern is
consistent over more than a few hours, up to several days. Fire smoke can cause especially
strong signals in these images.
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| Clear water |
High concentration of
suspended material |
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VI199707192212_susp_no14.jpg
Vancouver Island on July 19,1997 at 22:12 UTC
This image shows the computed suspended material image from the NOAA 14 satellite.
Bright water can be seen in the Fraser River plume (right, in the Strait of Georgia) and
in coastal fjords due to glacial silt (top, but harder to see between the digital
coastlines). The water off the south-west coast of Vancouver Island is brightened by a
major bloom event which can be tracked in a sequence of images through nearly the entire
month of July. Cloud is masked to black at the top left, though possibly some bright cloud
edges remain visible. |
Examples of NOAA thermal
images:
These samples show the thermal images from band 4. Images like this are used to measure
surface temperatures and temperature patterns that are important for fisheries management
and for understanding patterns of coastal currents and upwelling. Thermal images also show
patterns of Arctic ice during the winter darkness. We aren't currently able to use
the thermal images to measure temperature as they are not calibrated and the colour
palette is stretched to show the most contrast between the temperatures that are visible.
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| COLD
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black to blue, green,
yellow, red, white indicating progressively warmer surfaces. |
HOT |
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BS199702171543_ther_no12.jpg Beaufort
Sea on February 17,1997 at 15:43 UTC from NOAA 12. |
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QC199503012039_ther_no14.jpg Queen
Charlotte Islands on March 1,1995 at 20:39 UTC from NOAA 14. |
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AN199803012254_ther_NO14.jpg Anchorage,
Alaska on March 1,1998 at 22:54 UTC from NOAA 14 |
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VI199206240108_ther_no11.jpg
Vancouver Island on June 23,1992 at 16:05 PDT , showing a meandering stream of cold
water moving south from the Brooks Peninsula along the edge of the continental shelf, and
winding into an eddy west of Cape Flattery. There is a thin band of cold up-welled water
along the Pacific coast of Washington. Warmer water is red, with colder water yellow to
green to blue.
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BS199312271906_ther_no09.jpg
Western Canadian Arctic taken at 10:15 PST on December 27 1993 at a season when visible
and near-infrared bands show only darkness. The image uses thermal radiation to show
patterns of sea ice in the Beaufort Sea and Amundsen Gulf. Open water where the ice has
moved apart is near freezing, but relatively warm (red). The ice is colder than the water
(red to yellow to green), with the surface of thicker ice coldest (blue). Some land
temperatures on Banks Island at the right of the image are even colder (black). In
Amundsen Gulf, south of Banks Island, ice has recently broken up. Fainter patterns show
where a larger area of thinner (less-cold) ice in Amundsen Gulf formed relatively
recently, after ice was cleared (up to the curved boundary in the lower right of the
image) into the Beaufort Sea, probably by a wind from the east. Streaks of a relatively
warm haze cross the lower left of the image. |
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