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 Characteristics Band Wavelength (  m) Applications Visible Cloud, snow and ice monitoring Near IR Water, vegetation and agricultural surveys Short Wave IR 3A Snow, ice and cloud discrimination Medium Wave IR 3B Sea surface temperature, volcano, forest fire activity Thermal IR Sea surface temperature, soil moisture Thermal IR 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: Ch 1, Ch 2 express data in terms of radiance or reflectance Ch 2 - Ch 1 Ch 2 -Ch 1 /Ch 2 +Ch 1

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 (  m) 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:  m –Multispectral: ; ; ;  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) (green) (red) (NIR) Panchromatic

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