Satellite Images

Similar idea as aerial photos Similar idea as aerial photos Have some of the same uses Have some of the same uses Basis for mappingBasis for mapping Image interpretationImage interpretation Backdrop for mapBackdrop for map …but there are some important differences… …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 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 detectorInstantaneous field of view (IFOV) – corresponds to size of area viewed by each detector Scanner builds 2D image of surface by recording reflected energy Scanner builds 2D image of surface by recording reflected energy

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

Landsat Launched July 1972 Launched July 1972 First system designed to gather data about Earth’s land surface First system designed to gather data about Earth’s land surface Three imaging scanners onboard Three imaging scanners onboard Video cameraVideo camera Multispectral scannerMultispectral scanner Thematic MapperThematic Mapper Enhanced Thematic MapperEnhanced Thematic Mapper Revisit time days Revisit time days

MODIS Collects data at range of wavelengths from visible through thermal infrared Collects data at range of wavelengths from visible through thermal infrared Resolution between 250 meters and 1 kilometer Resolution between 250 meters and 1 kilometer Revisit time 1-2 days at 1 kilometer resolution Revisit time 1-2 days at 1 kilometer resolution

Which to use? Satellite or Aerial? Take the following factors into account Take the following factors into account Spatial resolution requiredSpatial resolution required Size of analysis areaSize of analysis area PricePrice Time constraintsTime constraints Post processingPost processing Mosaicing of Aerials Mosaicing of Aerials Spectral requirementsSpectral requirements Digital vs Film formatDigital vs Film format