meteorological satellites – national oceanographic and atmospheric administration (noaa)-polar...
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Meteorological satellites – National Oceanographic and Atmospheric Administration (NOAA)-Polar
Orbiting Environmental Satellite (POES)
• Orbital characteristics – Sensor: Advanced Very High Resolution Radiometer
(AVHRR) – Maximum resolution: 1.1 km at nadir (becoming
even coarser with increases in the viewing angle off-nadir)
– Width: 2400 km– Images the earth once every 24 hours– 1978 to present – NOAA satellites provide daily (visible) and twice-
daily (thermal IR) coverage
AVHRR Sensor CharacteristicsBand Wavelength (m) Applications
Visible 1 0.58-0.68 Cloud, snow and ice monitoring
Near IR 2 0.725-1.10 Water, vegetation and agricultural surveys
Short Wave IR 3A 1.58-1.64 Snow, ice and cloud discrimination
Medium Wave IR 3B 3.55-3.93 Sea surface temperature, volcano, forest fire activity
Thermal IR 4 10.3-11.3 Sea surface temperature, soil moisture
Thermal IR 5 11.3-12.5 Sea surface temperature, soil moisture
Example coverage of NOAA AVHRR
Vegetation Indices
• Various mathematical combinations of AVHRR channel 1 (visible band) and 2 (near IR band) data have been found to be sensitive indicators of the presence and condition of green vegetation.
Vegetation Indices
•
Vegetation Indices
• Two such indices:
VI (Vegetation Index):
Normalized Difference Vegetation Index:
Ch1, Ch2 express data in terms of radiance or reflectance
Ch2 - Ch1
Ch2 -Ch1 /Ch2 +Ch1
Vegetation Indices
• Vegetated areas will yield high values for both indices because of their high near-IR reflectance and low visible reflectance.
• Clouds, water, snow have larger visible reflectance than near-IR, yielding negative values.
• Rock and bare soils have similar reflectances, resulting in near zero indices.
Vegetation Indices
• The NDVI is preferable because it compensates for changing illumination conditions, surface slopes, aspect and other extraneous factors.
Vegetation Indices
• A number of factors can influence NDVI observations (unrelated to vegetation):
– Atmospheric effects – Radiometric response characteristics of the
sensor– Variability in incident solar radiation– Off-nadir viewing effects (±55° for AVHRR)
NOAA 6 AVHRR band 4
NOAA 6 AVHRR band 4 thermal IR image (10.5-11.5m)
Dark tones represent warm radiant temperatures and light tones represent cool radiant temperatures. This image was acquired 24 April 1982, at about 7:30AM local time.
NOAA 6 AVHRR
High-resolution ‘small’ satellites
• Small satellites are those with low orbit with less mass compared with those major satellites
• High resolution data • Allow design for special purposes • Low cost and flexible to launch • Can be designed, manufactured and
launched by, e.g. universities
1-m resolution satellites
IKONOS
• Launched on 24 September 1999
• Commercial remote sensing system operated by Space Imaging Inc. of Denver, Colorado, USA
IKONOS Orbit
• Type: Sun-Synchronous• Altitude: 681 Km• Inclination: 98.1 degree• Period: 98 minute• Off-Nadir Revisit: 2.9 days at 1-m
resolution, 1.5 days at 1.5 m at 40°
IKONOS (cont.)
• Ground resolution: 1-m panchromatic; 4-m multispectral
• Imagery Spectral Response – Panchromatic: 0.45-0.90 m – Multispectral: 0.45-0.52; 0.52-0.60; 0.63-0.69; 0.76-
0.90 m
• Nominal swath width: 13 km at nadir • Areas of interest (Single scene ) : 13x13 km • The IKONIS satellite is equipped with onboard
GPS, enabling it to acquire imagery with very high positional accuracy
• Radiometric digitization: 11 bits
Sensor Characteristics (IKONOS)
Spectral band Wavelength (m(
Resolution (m)
1 (blue) 0.40-0.52 4
2 (green) 0.52-0.60 4
3 (red) 0.63-0.69 4
4 (NIR) 0.76-0.90 4
Panchromatic 0.45-0.90 1
IKONOS Colour Image
Beijing City 22/10/1999
IKONOS Colour Image
Sydney Olympic Park 2000
IKONOS Colour Image
IKONOS Images
Manhattan: before (left) and after (right) 11 September 2001 attack
IKONOS Images
The Pentagon: before (left) and after (right) 11 September 2001 attack