Satellite Images

Satellite Images

Similar idea as aerial photos Have some of the same uses

• Basis for mapping• Image interpretation• Backdrop for map

…but there are some important differences…

How Satellite Images differ from Aerial Images

Have spectral ranges beyond aerial film Very high perspective

• Reduces terrain distortion Cover large areas

• High cost for small area coverage May require specialized image

processing Image acquisition must be scheduled

days or weeks in advance• Follow fixed flight schedules

Lower effective resolution

Basic Principles

Scanners on satellite operate by pointing detectors at area to be imaged• Instantaneous field of view (IFOV) –

corresponds to size of area viewed by each detector

Scanner builds 2D image of surface by recording reflected energy

Ikonos

High-resolution Launched September 1999 1-meter panchromatic infrared 4-meter visible/infrared 13 kilometer swath Revisit times 1-3 days

Landsat

Launched July 1972 First system designed to gather data

about Earth’s land surface Three imaging scanners onboard

• Video camera• Multispectral scanner• Thematic Mapper• Enhanced Thematic Mapper

Revisit time 16-18 days

MODIS

Collects data at range of wavelengths from visible through thermal infrared

Resolution between 250 meters and 1 kilometer

Revisit time 1-2 days at 1 kilometer resolution

Which to use?Satellite or Aerial?

Take the following factors into account• Spatial resolution required• Size of analysis area• Price• Time constraints• Post processing

Mosaicing of Aerials• Spectral requirements• Digital vs Film format