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